global warming compare and contrast essay

What’s the difference between climate change and global warming?

The terms “global warming” and “climate change” are sometimes used interchangeably, but "global warming" is only one aspect of climate change.

“Global warming” refers to the long-term warming of the planet. Global temperature shows a well-documented rise since the early 20th century and most notably since the late 1970s. Worldwide since 1880, the average surface temperature has risen about 1 ° C (about 2 ° F), relative to the mid-20th century baseline (of 1951-1980). This is on top of about an additional 0.15 ° C of warming from between 1750 and 1880.

“Climate change” encompasses global warming, but refers to the broader range of changes that are happening to our planet. These include rising sea levels; shrinking mountain glaciers; accelerating ice melt in Greenland, Antarctica and the Arctic; and shifts in flower/plant blooming times. These are all consequences of warming, which is caused mainly by people burning fossil fuels and putting out heat-trapping gases into the air.

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What's the difference between global warming and climate change?

Global warming refers only to the Earth’s rising surface temperature, while climate change includes warming and the “side effects” of warming—like melting glaciers, heavier rainstorms, or more frequent drought. Said another way, global warming is one symptom of the much larger problem of human-caused climate change.

Global warming is just one symptom of the much larger problem of climate change. NOAA Climate.gov cartoon by Emily Greenhalgh.

Another distinction between global warming and climate change is that when scientists or public leaders talk about global warming these days, they almost always mean human -caused warming—warming due to the rapid increase in carbon dioxide and other greenhouse gases from people burning coal, oil, and gas.

Climate change, on the other hand, can mean human-caused changes or natural ones, such as ice ages. Besides burning fossil fuels, humans can cause climate changes by emitting aerosol pollution—the tiny particles that reflect sunlight and cool the climate— into the atmosphere, or by transforming the Earth's landscape, for instance, from carbon-storing forests to farmland.

A climate change unlike any other

The planet has experienced climate change before: the Earth’s average temperature has fluctuated throughout the planet’s 4.54 billion-year history. The planet has experienced long cold periods ("ice ages") and warm periods ("interglacials") on 100,000-year cycles for at least the last million years.

Previous warming episodes were triggered by small increases in how much sunlight reached Earth’s surface and then amplified by large releases of carbon dioxide from the oceans as they warmed (like the fizz escaping from a warm soda).

Increases and decreases in global temperature during the naturally occurring ice ages of the past 800,000 years, ending with the early twentieth century. NOAA Climate.gov graph by Fiona Martin, based on EPICA Dome C ice core data provided by the Paleoclimatology Program at NOAA’s National Centers for Environmental Information.

Today’s global warming is overwhelmingly due to the increase in heat-trapping gases that humans are adding to the atmosphere by burning fossil fuels. In fact, over the last five decades, natural factors (solar forcing and volcanoes) would actually have led to a slight cooling of Earth’s surface temperature.

Global warming is also different from past warming in its rate. The current increase in global average temperature appears to be occurring much faster than at any point since modern civilization and agriculture developed in the past 11,000 years or so—and probably faster than any interglacial warm periods over the last million years.

Temperatures over most of the past 2000 years compared to the 1961-1990 average, based on proxy data (tree rings, ice cores, corals) and modern thermometer-based data. Over the past two millenia, climate warmed and cooled, but no previous warming episodes appear to have been as large and abrupt as recent global warming. NOAA Climate.gov graph by Fiona Martin, adapted from Figure 34.5 in the National Climate Assessment, based on data from Mann et al., 2008.

New understanding required new terms

Regardless of whether you say that climate change is all the side effects of global warming, or that global warming is one symptom of human-caused climate change, you’re essentially talking about the same basic phenomenon: the build up of excess heat energy in the Earth system.  So why do we have two ways of describing what is basically the same thing?

According to historian Spencer Weart , the use of more than one term to describe different aspects of the same phenomenon tracks the progress of scientists’ understanding of the problem.

As far back as the late 1800s, scientists were hypothesizing that industrialization, driven by the burning of fossil fuels for energy, had the potential to modify the climate. For many decades, though, they weren’t sure whether cooling (due to reflection of sunlight from pollution) or warming (due to greenhouse gases) would dominate.

By the mid-1970s, however, more and more evidence suggested warming would dominate and that it would be unlike any previous, naturally triggered warming episode. The phrase “global warming” emerged to describe that scientific consensus.

Change in temperature (degrees per century) from 1900-2014. Gray areas indicate where there is insufficient data to detect a long-term trend. NOAA Climate.gov map, based on NOAAGlobalTemp data from NOAA's National Centers for Environmental Information.

But over subsequent decades, scientists became more aware that global warming was not the only impact of excess heat absorbed by greenhouse gases.  Other changes—sea level rise, intensification of the water cycle, stress on plants and animals—were likely to be far more important to our daily lives and economies. By the 1990s, scientists increasingly used “human-caused climate change” to describe the challenge facing the planet.

The bottom line

Today’s global warming is an unprecedented type of climate change, and it is driving a cascade of side effects in our climate system. It’s these side effects, such as changes in sea level along heavily populated coastlines and the worldwide retreat of mountain glaciers that millions of people depend on for drinking water and agriculture, that are likely to have a much greater impact on society than temperature change alone.

Broecker, W. S. (1975). Climatic Change: Are We on the Brink of a Pronounced Global Warming? Science , 189(4201), 460–463.   http://doi.org/10.1126/science.189.4201.460

Climate Data Primer . Climate.gov.

Gillett, N. P., V. K. Arora, G. M. Flato, J. F. Scinocca, and K. von Salzen, 2012: Improved constraints on 21st-century warming derived using 160 years of temperature observations. Geophysical Research Letters, 39, 5, doi:10.1029/2011GL050226. [Available online at http://onlinelibrary.wiley.com/doi/10.1029/2011GL050226/pdf ]

Global Warming FAQ . Climate.gov.

How do we know the world has warmed? by J. J. Kennedy, P. W. Thorne, T. C. Peterson, R. A. Ruedy, P. A. Stott, D. E. Parker, S. A. Good, H. A. Titchner, and K. M. Willett, 2010: [in " State of the Climate in 2009 "]. Bull. Amer. Meteor. Soc., 91 (7), S79-106.

Huber, M., and R. Knutti, 2012: Anthropogenic and natural warming inferred from changes in Earth’s energy balance. Nature Geoscience, 5, 31-36, doi:10.1038/ngeo1327. [Available online at http://www.nature.com/ngeo/journal/v5/n1/pdf/ngeo1327.pdf ]

Jouzel, J., et al.  2007. EPICA Dome C Ice Core 800KYr Deuterium Data and Temperature Estimates.   IGBP PAGES/World Data Center for Paleoclimatology  Data Contribution Series # 2007-091. NOAA/NCDC Paleoclimatology Program, Boulder CO, USA.

Mann, M. E., Zhang, Z., Hughes, M. K., Bradley, R. S., Miller, S. K., Rutherford, S., & Ni, F., 2008: Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia. Proceedings of the National Academy of Sciences, 105(36), 13252-13257. doi: 10.1073/pnas.0805721105.

Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment . U.S. Global Change Research Program, 841 pp. doi:10.7930/J0Z31WJ2. Online at: nca2014.globalchange.gov

National Academy of Sciences, Climate Research Board, Carbon Dioxide and Climate: A Scientific Assessment (Jules Charney, Chair) . (1979). Washington, DC: National Academy of Sciences. [Online (pdf)] http://web.atmos.ucla.edu/~brianpm/download/charney_report.pdf

Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, P. Thorne, R. Vose, M. Wehner, J. Willis, D. Anderson, V. Kharin, T. Knutson, F. Landerer, T. Lenton, J. Kennedy, and R. Somerville, 2014: Appendix 4: Frequently Asked Questions. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 790-820. doi:10.7930/J0G15XS3

Weart, S. (2008). Timeline (Milestones). In The Discovery of Global Warming . [Online] American Institute of Physics website.

What's in a Name? Global Warming vs. Climate Change . NASA.

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Home — Essay Samples — Environment — Environment Problems — Global Warming

Argumentative Essays on Global Warming

Global warming: a critical analysis through essays.

The purpose of global warming essay topics is to ignite your creativity and personal interest in one of the most pressing issues of our time. Choosing the right topic is crucial, as it can greatly influence both the depth of your research and the impact of your arguments.

Global Warming Essay Topics

Different types of essays allow you to explore global warming from various angles, whether it be through an argumentative lens, a compare and contrast approach, descriptive insights, persuasive arguments, or narrative storytelling. Below, you will find a curated list of topics suitable for each essay type, accompanied by introduction and conclusion paragraph examples to help structure your essay effectively.

Global Warming Argumentative Essay Topics

• Topic: The Effectiveness of Current Policies on Reducing Carbon Emissions
• Thesis Statement: Current policies need significant strengthening to effectively reduce carbon emissions and combat global warming.

Introduction Example: As global warming poses a significant threat to our planet, the effectiveness of current policies to reduce carbon emissions has come under scrutiny. This essay will argue that while some policies have made progress, they are largely insufficient to meet the global targets set by the Paris Agreement.

Conclusion Example: In conclusion, the analysis demonstrates that current policies, though a step in the right direction, fall short of the aggressive action required to mitigate global warming. It calls for a global reevaluation and reinforcement of policies to ensure a sustainable future.

Global Warming Compare and Contrast Essays

• Topic: Renewable Energy vs. Fossil Fuels: Impacts on Global Warming
• Thesis Statement: Renewable energy sources offer a cleaner, more sustainable alternative to fossil fuels, making them essential in the fight against global warming.

Introduction Example: The debate between renewable energy and fossil fuels is at the forefront of the global warming discussion. This essay will compare and contrast the environmental impacts of both energy sources, highlighting the superiority of renewables in combating global warming.

Conclusion Example: The comparison clearly shows that renewable energy not only reduces the carbon footprint but also is a viable alternative to fossil fuels, underscoring the need for a global shift towards renewables to mitigate the effects of global warming.

Descriptive Essays on Global Warming

• Topic: The Visible Effects of Global Warming on Arctic Wildlife
• Thesis Statement: The devastating effects of global warming on Arctic wildlife underscore the urgent need for global environmental policies.

Introduction Example: Global warming has had a profound impact on Arctic wildlife, with visible effects that signal a broader ecological crisis. This essay aims to describe these impacts in detail, drawing attention to the urgent need for action.

Conclusion Example: In summarizing the dire situation in the Arctic, it becomes clear that global warming is not a distant threat but a current reality, necessitating immediate and decisive action to protect our planet's biodiversity.

Persuasive Essays

• Topic: The Role of Individuals in Combating Global Warming
• Thesis Statement: Individual efforts are crucial and effective in the fight against global warming, complementing larger-scale initiatives.

Introduction Example: While the fight against global warming often focuses on governmental and corporate actions, the role of individuals cannot be underestimated. This essay will persuade readers that individual actions, though seemingly small, can collectively make a significant impact on combating global warming.

Conclusion Example: As demonstrated, individual actions play a pivotal role in combating global warming. It is through collective effort at every level of society that we can hope to address this global challenge effectively.

Narrative Essays

• Topic: A Personal Journey to Reduce My Carbon Footprint
• Thesis Statement: Individual actions to reduce carbon footprints can inspire change and contribute significantly to combating global warming.

Introduction Example: Embarking on a personal journey to reduce my carbon footprint was both enlightening and challenging. Through this narrative, I aim to share my experiences, the obstacles I faced, and the impact of my actions on a personal level.

Conclusion Example: My journey reveals that while individual actions may seem small in the grand scheme of global warming, they are powerful catalysts for change, underscoring the importance of personal responsibility in the global effort to combat climate change.

Engagement and Creativity

As you delve into your essay on global warming, we encourage you to select a topic that not only aligns with your academic goals but also sparks your interest. Let your creativity guide your research and argumentation, making your essay not just an academic exercise, but a personal exploration of one of the most urgent issues facing our world today.

Educational Value

Writing about global warming is not only an opportunity to contribute to an important global conversation but also a chance to develop valuable academic skills. Whether you're crafting an argumentative, compare and contrast, descriptive, persuasive, or narrative essay, you're engaging in critical thinking, research, and persuasive communication—skills that are invaluable in both academic and professional settings.

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A Modest Proposal: How to End Global Warming

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Global warming refers to the long-term increase in Earth's average surface temperature primarily caused by the buildup of greenhouse gases in the atmosphere.

Greta Thunberg: a prominent Swedish environmental activist who gained international recognition for her efforts to combat climate change. Al Gore: an American politician and environmentalist who has been instrumental in raising awareness about global warming. He wrote the book "An Inconvenient Truth" and co-founded the Climate Reality Project, advocating for climate change solutions and promoting sustainable practices. Sir David Attenborough: a renowned British naturalist and broadcaster who has dedicated his career to documenting the wonders of the natural world. In recent years, he has become an influential voice in raising awareness about the impacts of global warming through his documentaries and speeches. Dr. James Hansen: an American climatologist and former NASA scientist. He is known for his research on climate change and his efforts to communicate the urgency of addressing global warming. Elon Musk: the CEO of Tesla and SpaceX, has played a significant role in promoting renewable energy and sustainable transportation. Through Tesla, Musk has popularized electric vehicles and accelerated the transition away from fossil fuels, contributing to the fight against global warming.

The historical context of global warming can be traced back to the late 19th century when scientists first began to recognize the potential impact of human activities on the Earth's climate. In the early 20th century, researchers such as Svante Arrhenius hypothesized that the burning of fossil fuels could lead to an increase in atmospheric carbon dioxide levels and subsequently cause a rise in global temperatures. During the mid-20th century, advancements in technology and industrialization led to a significant increase in greenhouse gas emissions. The post-World War II era marked a period of rapid economic growth and widespread use of fossil fuels, further contributing to the accumulation of greenhouse gases in the atmosphere. In the 1980s and 1990s, scientific consensus on the reality of global warming began to solidify. The establishment of the Intergovernmental Panel on Climate Change (IPCC) in 1988 provided a platform for scientists and policymakers to collaborate and assess the scientific evidence surrounding climate change. The historical context of global warming also includes international efforts to address this issue. Key milestones include the adoption of the United Nations Framework Convention on Climate Change (UNFCCC) in 1992 and the subsequent negotiations that led to the Kyoto Protocol in 1997. These agreements aimed to promote international cooperation and reduce greenhouse gas emissions.

1. Increase in greenhouse gases and combustion of fossil fuels. 2. Exponential increase in population. 3. Destruction of ecosystems and deforestation. 4. Destruction of marine ecosystems.

1. Melting of polar ice caps and rising sea levels. 2. Changes to ecosystems. 3. Mass migrations. 4. Acidity of our oceans. 5. Species extinction. 6. Extreme meteorological phenomena.

Calculating carbon footprint. Reducing greenhouse gases. Offsetting carbon emissions.

Public opinion on the topic of global warming varies, but there is a growing recognition and concern about its impacts. Over the years, surveys and polls have indicated that a majority of the global population acknowledges the reality of global warming and considers it a significant issue. Many individuals are increasingly aware of the scientific consensus that human activities, particularly the burning of fossil fuels, contribute to the increase in greenhouse gases and subsequent global temperature rise. The severity of extreme weather events, melting ice caps, and rising sea levels further emphasize the urgency of addressing global warming. However, public opinion on specific aspects of global warming, such as its causes and potential solutions, can be diverse and influenced by various factors including political beliefs, cultural values, and economic considerations. Debates continue regarding the extent of human influence on climate change and the appropriate measures to mitigate its effects. Efforts to raise awareness and educate the public about global warming have led to increased activism, calls for policy changes, and the promotion of sustainable practices. Public opinion plays a crucial role in shaping political will and policy decisions, influencing the development and implementation of climate change mitigation and adaptation strategies.

The topic of global warming has garnered significant representation in both media and literature, reflecting the urgency and importance of addressing climate change. In media, documentaries like "An Inconvenient Truth" by Al Gore and "Before the Flood" by Leonardo DiCaprio have gained widespread attention for their compelling exploration of the environmental crisis. These films present scientific evidence, personal narratives, and expert interviews to raise awareness and provoke action. In literature, works such as "The Sixth Extinction" by Elizabeth Kolbert and "This Changes Everything: Capitalism vs. The Climate" by Naomi Klein offer in-depth analyses of global warming's causes and consequences. These books provide rigorous research, critical perspectives, and propose alternative approaches to mitigate climate change. Moreover, literary works of fiction, such as "Flight Behavior" by Barbara Kingsolver and "Oryx and Crake" by Margaret Atwood, employ global warming as a central theme. These novels explore the social, political, and ecological implications of a changing climate, using storytelling to engage readers on a personal and emotional level. News outlets regularly cover stories related to global warming, reporting on scientific studies, climate events, and policy debates. Newspapers, magazines, and online platforms offer articles that delve into the impacts of climate change on various sectors, including agriculture, health, and the environment.

1. The global average temperature has risen by approximately 1 degree Celsius since the pre-industrial era. 2. According to the Intergovernmental Panel on Climate Change (IPCC), if global warming exceeds 1.5 degrees Celsius, it could lead to irreversible and catastrophic effects, such as widespread species extinction, severe weather events, and rising sea levels. 3. The concentration of carbon dioxide (CO2) in the Earth's atmosphere is the highest it has been in at least 800,000 years, primarily due to human activities. CO2 is a greenhouse gas that traps heat and contributes to the warming of the planet. 4. Glacier retreat is a significant consequence of global warming. Over the past century, glaciers around the world have lost a substantial amount of ice, affecting water supplies, ecosystems, and contributing to sea-level rise. 5. The economic costs of climate change are substantial. According to estimates by the World Bank, the impacts of global warming, including extreme weather events, reduced agricultural productivity, and health-related expenses, could lead to an annual loss of 5-10% of global GDP by the end of the century.

The topic of global warming is of utmost importance to write an essay about due to its far-reaching implications for our planet and future generations. Global warming, driven by human activities, has led to unprecedented changes in our climate system, affecting ecosystems, economies, and human well-being. By exploring this topic in an essay, we can increase awareness and understanding of the causes, impacts, and potential solutions to address global warming. An essay on global warming provides an opportunity to delve into the scientific evidence supporting climate change, highlighting the role of greenhouse gas emissions, deforestation, and other factors. It allows for an examination of the consequences, such as rising temperatures, sea-level rise, and extreme weather events, on various aspects of life, including agriculture, biodiversity, and human health. Furthermore, discussing global warming in an essay encourages critical thinking and engagement with the complex social, political, and economic dimensions of the issue. It prompts us to consider the ethical responsibilities we have towards future generations, as well as the importance of international cooperation and policy actions to mitigate and adapt to climate change.

1. Intergovernmental Panel on Climate Change. (2018). Global Warming of 1.5°C. Cambridge University Press. 2. Solomon, S., Qin, D., Manning, M., Alley, R., Berntsen, T., Bindoff, N., ... & Zhang, P. (Eds.). (2007). Climate change 2007: the physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. 3. NASA. (2021). Global Climate Change: Vital Signs of the Planet. Retrieved from https://climate.nasa.gov/ 4. Union of Concerned Scientists. (2020). The Science of Climate Change. Retrieved from https://www.ucsusa.org/resources/science-climate-change 5. National Oceanic and Atmospheric Administration. (2019). Climate.gov. Retrieved from https://www.climate.gov/ 6. World Meteorological Organization. (2021). State of the Global Climate 2020. Retrieved from https://public.wmo.int/en/resources/state-of-the-global-climate 7. National Geographic. (2021). Climate Change. Retrieved from https://www.nationalgeographic.com/environment/global-warming/ 8. IPCC. (2014). Climate Change 2014: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press. 9. United Nations. (2015). Paris Agreement. Retrieved from https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement 10. Environmental Protection Agency. (2021). Climate Change. Retrieved from https://www.epa.gov/climate-change

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What is the difference between global warming and climate change?

Although people tend to use these terms interchangeably, global warming is just one aspect of climate change. “Global warming” refers to the rise in global temperatures due mainly to the increasing concentrations of greenhouse gases in the atmosphere. “Climate change” refers to the increasing changes in the measures of climate over a long period of time – including precipitation, temperature, and wind patterns.

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Whats in a name global warming vs. climate change.

The Internet is full of references to global warming . The Union of Concerned Scientists website on climate change is titled "Global Warming," just one of many examples. But we don't use global warming much on this website. We use the less appealing "climate change." Why?

To a scientist, global warming describes the average global surface temperature increase from human emissions of greenhouse gases. Its first use was in a 1975 Science article by geochemist Wallace Broecker of Columbia University's Lamont-Doherty Geological Observatory: "Climatic Change: Are We on the Brink of a Pronounced Global Warming?"1

Broecker's term was a break with tradition. Earlier studies of human impact on climate had called it "inadvertent climate modification."2 This was because while many scientists accepted that human activities could cause climate change, they did not know what the direction of change might be. Industrial emissions of tiny airborne particles called aerosols might cause cooling, while greenhouse gas emissions would cause warming. Which effect would dominate?

For most of the 1970s, nobody knew. So "inadvertent climate modification," while clunky and dull, was an accurate reflection of the state of knowledge.

The first decisive National Academy of Science study of carbon dioxide's impact on climate, published in 1979, abandoned "inadvertent climate modification." Often called the Charney Report for its chairman, Jule Charney of the Massachusetts Institute of Technology in Cambridge, declared: "if carbon dioxide continues to increase, [we find] no reason to doubt that climate changes will result and no reason to believe that these changes will be negligible."3

In place of inadvertent climate modification, Charney adopted Broecker's usage. When referring to surface temperature change, Charney used "global warming." When discussing the many other changes that would be induced by increasing carbon dioxide, Charney used "climate change." Definitions

Global warming: the increase in Earth’s average surface temperature due to rising levels of greenhouse gases.

Climate change: a long-term change in the Earth’s climate, or of a region on Earth.

Within scientific journals, this is still how the two terms are used. Global warming refers to surface temperature increases, while climate change includes global warming and everything else that increasing greenhouse gas amounts will affect.

During the late 1980s one more term entered the lexicon, “global change.” This term encompassed many other kinds of change in addition to climate change. When it was approved in 1989, the U.S. climate research program was embedded as a theme area within the U.S. Global Change Research Program.

But global warming became the dominant popular term in June 1988, when NASA scientist James E. Hansen had testified to Congress about climate, specifically referring to global warming. He said: "global warming has reached a level such that we can ascribe with a high degree of confidence a cause and effect relationship between the greenhouse effect and the observed warming."4 Hansen's testimony was very widely reported in popular and business media, and after that popular use of the term global warming exploded. Global change never gained traction in either the scientific literature or the popular media.

But temperature change itself isn't the most severe effect of changing climate. Changes to precipitation patterns and sea level are likely to have much greater human impact than the higher temperatures alone. For this reason, scientific research on climate change encompasses far more than surface temperature change. So "global climate change" is the more scientifically accurate term. Like the Intergovernmental Panel on Climate Change, we've chosen to emphasize global climate change on this website, and not global warming.

1 Wallace Broecker, "Climatic Change: Are We on the Brink of a Pronounced Global Warming?" Science, vol. 189 (8 August 1975), 460-463.

2 For example, see: MIT, Inadvertent Climate Modification: Report of the Study of Man's Impact on Climate (Cambridge, Mass.: MIT Press, 1971).

3National Academy of Science, Carbon Dioxide and Climate, Washington, D.C., 1979, p. vii.

4U.S. Senate, Committee on Energy and Natural Resources, "Greenhouse Effect and Global Climate Change, part 2" 100th Cong., 1st sess., 23 June 1988, p. 44.

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The past, present and future of climate change

Climate issue: replacing the fossil-fuel technology which is reshaping the climate remains a massive task.

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I N THE EARLY 19th century Joseph Fourier, a French pioneer in the study of heat, showed that the atmosphere kept the Earth warmer than it would be if exposed directly to outer space. By 1860 John Tyndall, an Irish physicist, had found that a key to this warming lay in an interesting property of some atmospheric gases, including carbon dioxide. They were transparent to visible light but absorbed infrared radiation, which meant they let sunlight in but impeded heat from getting out. By the turn of the 20th century Svante Arrhenius, a Swedish chemist, was speculating that low carbon-dioxide levels might have caused the ice ages, and that the industrial use of coal might warm the planet.

What none foresaw was how fast, and how far, the use of fossil fuels would grow (see chart above). In 1900 the deliberate burning of fossil fuels—almost entirely, at the time, coal—produced about 2bn tonnes of carbon dioxide. By 1950 industrial emissions were three times that much. Today they are close to 20 times that much.

That explosion of fossil-fuel use is inseparable from everything else which made the 20th century unique in human history. As well as providing unprecedented access to energy for manufacturing, heating and transport, fossil fuels also made almost all the Earth’s other resources vastly more accessible. The nitrogen-based explosives and fertilisers which fossil fuels made cheap and plentiful transformed mining, warfare and farming. Oil refineries poured forth the raw materials for plastics. The forests met the chainsaw.

In no previous century had the human population doubled. In the 20th century it came within a whisker of doubling twice. In no previous century had world GDP doubled. In the 20th century it doubled four times and then some.

An appendix to a report prepared by America’s Presidential Science Advisory Committee in 1965 marks the first time that politicians were made directly aware of the likely climate impact of all this. In the first half of the century scientists believed that almost all the carbon dioxide given off by industry would be soaked up by the oceans. But Roger Revelle, an oceanographer, had shown in the 1950s that this was not the case. He had also instituted efforts to measure year-on-year changes in the atmosphere’s carbon-dioxide level. By 1965 it was clear that it was steadily rising.

The summary of what that rise meant, novel when sent to the president, is now familiar. Carbon stored up in the crust over hundreds of millions of years was being released in a few generations; if nothing were done, temperatures and sea levels would rise to an extent with no historic parallel. Its suggested response seems more bizarre: trillions of ping-pong balls on the ocean surface might reflect back more of the sun’s rays, providing a cooling effect.

The big difference between 1965 and now, though, is what was then a peculiar prediction is now an acute predicament. In 1965 the carbon-dioxide level was 320 parts per million (ppm); unprecedented, but only 40ppm above what it had been two centuries earlier. The next 40ppm took just three decades. The 40ppm after that took just two. The carbon-dioxide level is now 408ppm, and still rising by 2ppm a year.

Records of ancient atmospheres provide an unnerving context for this precipitous rise. Arrhenius was right in his hypothesis that a large part of the difference in temperature between the ice ages and the warm “interglacials” that separated them was down to carbon dioxide. Evidence from Antarctic ice cores shows the two going up and down together over hundreds of thousands of years. In interglacials the carbon-dioxide level is 1.45 times higher than it is in the depths of an ice age. Today’s level is 1.45 times higher than that of a typical interglacial. In terms of carbon dioxide’s greenhouse effect, today’s world is already as far from that of the 18th century as the 18th century was from the ice age (see “like an ice age” chart).

Not all the difference in temperature between interglacials and ice ages was because of carbon dioxide. The reflection of sunlight by the expanded ice caps added to the cooling, as did the dryness of the atmosphere. But the ice cores make it clear that what the world is seeing is a sudden and dramatic shift in fundamental parameter of the planet’s climate. The last time the Earth had a carbon-dioxide level similar to today’s, it was on average about 3°C warmer. Greenland’s hills were green. Parts of Antarctica were fringed with forest. The water now frozen over those landscapes was in the oceans, providing sea levels 20 metres higher than today’s.

Ping-pong ding-dong

There is no evidence that President Lyndon Johnson read the 1965 report. He certainly didn’t act on it. The idea of deliberately changing the Earth’s reflectivity, whether with ping-pong balls or by other means, was outlandish. The idea that the fuels on which the American and world economies were based should be phased out would have seemed even more so. And there was, back then, no conclusive proof that humans were warming the Earth.

Proof took time. Carbon dioxide is not the only greenhouse gas. Methane and nitrous oxide trap heat, too. So does water vapour, which thereby amplifies the effects of the others. Because warmth drives evaporation, a world warmed by carbon dioxide will have a moister atmosphere, which will make it warmer still. But water vapour also condenses into clouds—some of which cool the world and some of which warm it further. Then and now, the complexities of such processes make precision about the amount of warming expected for a given carbon-dioxide level unachievable.

Further complexities abound. Burning fossil fuels releases particles small enough to float in the air as well as carbon dioxide. These “aerosols” warm the atmosphere, but also shade and thereby cool the surface below; in the 1960s and 1970s some thought their cooling power might overpower the warming effects of carbon dioxide. Volcanic eruptions also produce surface-cooling aerosols, the effects of which can be global; the brightness of the sun varies over time, too, in subtle ways. And even without such external “forcings”, the internal dynamics of the climate will shift heat between the oceans and atmosphere over various timescales. The best known such shifts, the El Niño events seen a few times a decade, show up in the mean surface temperature of the world as a whole.

These complexities meant that, for a time, there was doubt about greenhouse warming, which the fossil-fuel lobby deliberately fostered. There is no legitimate doubt today. Every decade since the 1970s has been warmer than the one before, which rules out natural variations. It is possible to compare climate models that account for just the natural forcings of the 20th century with those that take into account human activities, too. The effects of industry are not statistically significant until the 1980s. Now they are indisputable.

At the Earth Summit in Rio de Janeiro in 1992, around the time that the human effect on the climate was becoming clearly discernible, the nations of the world signed the UN Framework Convention on Climate Change ( UNFCCC ). By doing so they promised to “prevent dangerous anthropogenic interference with the climate system”.

Since then humans have emitted 765bn more tonnes of carbon dioxide; the 2010s have been, on average, some 0.5°C hotter than the 1980s. The Intergovernmental Panel on Climate Change ( IPCC ) estimates that mean surface temperature is now 1°C above what it was in the pre-industrial world, and rising by about 0.2°C a decade. In mid- to high-northern latitudes, and in some other places, there has already been a warming of 1.5°C or more; much of the Arctic has seen more than 3°C (see map).

The figure of 1.5°C matters because of the Paris agreement, signed by the parties to the UNFCCC in 2015. That agreement added targets to the original goal of preventing “dangerous interference” in the climate: the signatories promised to hold global warming “well below” 2°C above pre-industrial temperatures and to make “efforts to limit the temperature increase to 1.5°C”.

Neither 1.5°C nor 2°C has any particular significance outside these commitments. Neither marks a threshold beyond which the world becomes uninhabitable, or a tipping point of no return. Conversely, they are not limits below which climate change has no harmful effects. There must be thresholds and tipping points in a warming world. But they are not well enough understood for them to be associated with specific rises in mean temperature.

For the most part the harm warming will do—making extreme weather events more frequent and/or more intense, changing patterns of rainfall and drought, disrupting ecosystems, driving up sea levels—simply gets greater the more warming there is. And its global toll could well be so great that individual calamities add little.

At present further warming is certain, whatever the world does about its emissions. This is in part because, just as a pan of water on a hob takes time to boil when the gas below is lit, so the world’s mean temperature is taking time to respond to the heating imposed by the sky above. It is also because what matters is the total amount of greenhouse gas in the atmosphere, not the rate at which it increases. Lowering annual emissions merely slows the rate at which the sky’s heating effect gets stronger; surface warming does not come to an end until the greenhouse-gas level is no longer increasing at all. If warming is to be held to 1.5°C that needs to happen by around 2050; if it is to be kept well below 2°C there are at best a couple more decades to play with.

Revolution in reverse

Thus, in its simplest form, the 21st century’s supertanker-U-turn challenge: reversing the 20-fold increase in emissions the 20th century set in train, and doing so at twice the speed. Replacing everything that burns gas or coal or oil to heat a home or drive a generator or turn a wheel. Rebuilding all the steelworks; refashioning the cement works; recycling or replacing the plastics; transforming farms on all continents. And doing it all while expanding the economy enough to meet the needs and desires of a population which may well be half again as large by 2100 as it is today.

“Integrated assessment models”, which combine economic dynamics with assumptions about the climate, suggest that getting to zero emissions by 2050 means halving current emissions by 2030. No nation is on course to do that. The national pledges made at the time of the Paris agreement would, if met, see global emissions in 2030 roughly equivalent to today’s. Even if emissions decline thereafter, that suggests a good chance of reaching 3°C.

Some countries already emit less than half as much carbon dioxide as the global average. But they are countries where many people desperately want more of the energy, transport and resources that fossil fuels have provided richer nations over the past century. Some of those richer nations have now pledged to rejoin the low emitters. Britain has legislated for massive cuts in emissions by 2050. But the fact that legislation calls for something does not mean it will happen. And even if it did, at a global level it would remain a small contribution.

This is one of the problems of trying to stop warming through emission policies. If you reduce emissions and no one else does, you face roughly the same climate risk as before. If everyone else reduces and you do not, you get almost as much benefit as you would if you had joined in. It is a collective-action problem that only gets worse as mitigation gets more ambitious.

What is more, the costs and benefits are radically uncertain and unevenly distributed. Most of the benefit from curtailing climate change will almost certainly be felt by people in developing countries; most of the cost of emission cuts will be felt elsewhere. And most of the benefits will be accrued not today, but in 50 or 100 years.

It is thus fitting that the most striking recent development in climate politics is the rise of activism among the young. For people born, like most of the world’s current leaders, well before 1980, the second half of the 21st century seems largely hypothetical. For people born after 2000, like Greta Thunberg, a Swedish activist, and some 2.6bn others, it seems like half their lives. This gives moral weight to their demands that the Paris targets be met, with emissions halved by 2030. But the belief that this can be accomplished through a massive influx of “political will” severely underestimates the challenge.

It is true that, after a spectacular boom in renewable-energy installations, electricity from the wind and the sun now accounts for 7% of the world’s total generation. The price of such installations has tumbled; they are now often cheaper than fossil-fuel generating capacity, though storage capacity and grid modifications may make that advantage less at the level of the whole electricity system.

One step towards halving emissions by 2030 would be to ramp such renewable-electricity generation up to half the total. This would mean a fivefold-to-tenfold increase in capacity. Expanding hydroelectricity and nuclear power would lessen the challenge of all those square kilometres of solar panels and millions of windmills. But increased demand would heighten it. Last year world electricity demand rose by 3.7%. Eleven years of such growth would see demand in 2030 half as large again as demand in 2018. All that new capacity would have to be fossil-fuel-free.

And electricity is the easy part. Emissions from generating plants are less than 40% of all industrial emissions. Progress on reducing emissions from industrial processes and transport is far less advanced. Only 0.5% of the world’s vehicles are electric, according to Bloomberg NEF , a research firm. If that were to increase to 50% without increasing emissions the production of fossil-fuel-free electricity would have to shoot up yet further.

The investment needed to bring all this about would be unprecedented. So would the harm to sections of the fossil economy. According to Carbon Tracker, a think-tank, more than half the money the big oil companies plan to spend on new fields would be worthless in a world that halved emissions by 2030. The implications extend to geopolitics. A world in which the oil price is no longer of interest is one very different from that of the past century.

Putting off to tomorrow

Dislocation on such a scale might be undertaken if a large asteroid on a fixed trajectory were set to devastate North America on January 1st 2031. It is far harder to imagine when the victims are less readily identifiable and the harms less cosmically certain—even if they eventually turn out to be comparable in scale. Realising this, the climate negotiators of the world have, over the past decade, increasingly come to depend on the idea of “negative emissions”. Instead of not putting carbon dioxide into the atmosphere at all, put it in and take it out later. By evoking ever larger negative emissions later in the century it is possible to accept a later peak and a slower reduction while still being able to say that you will end up within the 1.5°C or 2°C limit (see “four futures” chart).

Unfortunately, technologies capable of delivering negative emissions of billions of tonnes a year for reasonable prices over decades do not exist. There are, though, ideas about how they could be brought into being. One favoured by modellers involves first growing plants, which suck up atmospheric carbon dioxide through photosynthesis, and then burning them in power stations which store the carbon dioxide they produce underground. A surmountable problem is that no such systems yet exist at scale. A much tougher one is that the amount of land required for growing all those energy crops would be enormous.

This opens up a dilemma. Given that reducing emissions seems certain not to deliver quickly enough, it would seem stupid not to put serious effort into developing better ways of achieving negative emissions. But the better such R & D makes the outlook for negative emissions appear, the more the impetus for prompt emissions reduction diminishes. Something similar applies for a more radical potential response, solar geoengineering, which like the ping-pong balls of 1965 would reflect sunlight back to space before it could warm the Earth. Researchers thinking about this all stress that it should be used to reduce the harm of carbon dioxide already emitted, not used as an excuse to emit more. But the temptation would be there.

Even if the world were doing enough to limit warming to 2°C, there would still be a need for adaptation. Many communities are not even well adapted to today’s climate. Adaptation is in some ways a much easier policy to pursue than emissions reduction. But it has disadvantages. It gets harder as things get worse. It has a strong tendency to be reactive. And it is most easily achieved by those with resources; people who are marginalised and excluded, who the IPCC finds tend to be most affected by climate change, have the least capacity to adapt to it. It can also fall prey to the “moral hazard” problem encountered by negative emissions and solar geoengineering.

None of this means adaptation is not worthwhile. It is vital, and the developed nations—developed thanks to fossil fuels—have a duty to help their poorer counterparts achieve it, a duty acknowledged in Paris, if as yet barely acted on. But it will not stabilise the climate that humans have, in their global growth spurt, destabilised. And it will not stop all the suffering that instability will bring. ■

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This article appeared in the Briefing section of the print edition under the headline “What goes up”

From the September 21st 2019 edition

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Human activity affects global surface temperatures by changing Earth ’s radiative balance—the “give and take” between what comes in during the day and what Earth emits at night. Increases in greenhouse gases —i.e., trace gases such as carbon dioxide and methane that absorb heat energy emitted from Earth’s surface and reradiate it back—generated by industry and transportation cause the atmosphere to retain more heat, which increases temperatures and alters precipitation patterns.

Global warming, the phenomenon of increasing average air temperatures near Earth’s surface over the past one to two centuries, happens mostly in the troposphere , the lowest level of the atmosphere, which extends from Earth’s surface up to a height of 6–11 miles. This layer contains most of Earth’s clouds and is where living things and their habitats and weather primarily occur.

Continued global warming is expected to impact everything from energy use to water availability to crop productivity throughout the world. Poor countries and communities with limited abilities to adapt to these changes are expected to suffer disproportionately. Global warming is already being associated with increases in the incidence of severe and extreme weather, heavy flooding , and wildfires —phenomena that threaten homes, dams, transportation networks, and other facets of human infrastructure. Learn more about how the IPCC’s Sixth Assessment Report, released in 2021, describes the social impacts of global warming.

Polar bears live in the Arctic , where they use the region’s ice floes as they hunt seals and other marine mammals . Temperature increases related to global warming have been the most pronounced at the poles, where they often make the difference between frozen and melted ice. Polar bears rely on small gaps in the ice to hunt their prey. As these gaps widen because of continued melting, prey capture has become more challenging for these animals.

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global warming , the phenomenon of increasing average air temperatures near the surface of Earth over the past one to two centuries. Climate scientists have since the mid-20th century gathered detailed observations of various weather phenomena (such as temperatures, precipitation , and storms) and of related influences on climate (such as ocean currents and the atmosphere’s chemical composition). These data indicate that Earth’s climate has changed over almost every conceivable timescale since the beginning of geologic time and that human activities since at least the beginning of the Industrial Revolution have a growing influence over the pace and extent of present-day climate change .

Giving voice to a growing conviction of most of the scientific community , the Intergovernmental Panel on Climate Change (IPCC) was formed in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Program (UNEP). The IPCC’s Sixth Assessment Report (AR6), published in 2021, noted that the best estimate of the increase in global average surface temperature between 1850 and 2019 was 1.07 °C (1.9 °F). An IPCC special report produced in 2018 noted that human beings and their activities have been responsible for a worldwide average temperature increase between 0.8 and 1.2 °C (1.4 and 2.2 °F) since preindustrial times, and most of the warming over the second half of the 20th century could be attributed to human activities.

AR6 produced a series of global climate predictions based on modeling five greenhouse gas emission scenarios that accounted for future emissions, mitigation (severity reduction) measures, and uncertainties in the model projections. Some of the main uncertainties include the precise role of feedback processes and the impacts of industrial pollutants known as aerosols , which may offset some warming. The lowest-emissions scenario, which assumed steep cuts in greenhouse gas emissions beginning in 2015, predicted that the global mean surface temperature would increase between 1.0 and 1.8 °C (1.8 and 3.2 °F) by 2100 relative to the 1850–1900 average. This range stood in stark contrast to the highest-emissions scenario, which predicted that the mean surface temperature would rise between 3.3 and 5.7 °C (5.9 and 10.2 °F) by 2100 based on the assumption that greenhouse gas emissions would continue to increase throughout the 21st century. The intermediate-emissions scenario, which assumed that emissions would stabilize by 2050 before declining gradually, projected an increase of between 2.1 and 3.5 °C (3.8 and 6.3 °F) by 2100.

Many climate scientists agree that significant societal, economic, and ecological damage would result if the global average temperature rose by more than 2 °C (3.6 °F) in such a short time. Such damage would include increased extinction of many plant and animal species, shifts in patterns of agriculture , and rising sea levels. By 2015 all but a few national governments had begun the process of instituting carbon reduction plans as part of the Paris Agreement , a treaty designed to help countries keep global warming to 1.5 °C (2.7 °F) above preindustrial levels in order to avoid the worst of the predicted effects. Whereas authors of the 2018 special report noted that should carbon emissions continue at their present rate, the increase in average near-surface air temperature would reach 1.5 °C sometime between 2030 and 2052, authors of the AR6 report suggested that this threshold would be reached by 2041 at the latest.

The AR6 report also noted that the global average sea level had risen by some 20 cm (7.9 inches) between 1901 and 2018 and that sea level rose faster in the second half of the 20th century than in the first half. It also predicted, again depending on a wide range of scenarios, that the global average sea level would rise by different amounts by 2100 relative to the 1995–2014 average. Under the report’s lowest-emission scenario, sea level would rise by 28–55 cm (11–21.7 inches), whereas, under the intermediate emissions scenario, sea level would rise by 44–76 cm (17.3–29.9 inches). The highest-emissions scenario suggested that sea level would rise by 63–101 cm (24.8–39.8 inches) by 2100.

The scenarios referred to above depend mainly on future concentrations of certain trace gases, called greenhouse gases , that have been injected into the lower atmosphere in increasing amounts through the burning of fossil fuels for industry, transportation , and residential uses. Modern global warming is the result of an increase in magnitude of the so-called greenhouse effect , a warming of Earth’s surface and lower atmosphere caused by the presence of water vapour , carbon dioxide , methane , nitrous oxides , and other greenhouse gases. In 2014 the IPCC first reported that concentrations of carbon dioxide, methane, and nitrous oxides in the atmosphere surpassed those found in ice cores dating back 800,000 years.

Of all these gases, carbon dioxide is the most important, both for its role in the greenhouse effect and for its role in the human economy. It has been estimated that, at the beginning of the industrial age in the mid-18th century, carbon dioxide concentrations in the atmosphere were roughly 280 parts per million (ppm). By the end of 2022 they had risen to 419 ppm, and, if fossil fuels continue to be burned at current rates, they are projected to reach 550 ppm by the mid-21st century—essentially, a doubling of carbon dioxide concentrations in 300 years.

A vigorous debate is in progress over the extent and seriousness of rising surface temperatures, the effects of past and future warming on human life, and the need for action to reduce future warming and deal with its consequences. This article provides an overview of the scientific background related to the subject of global warming. It considers the causes of rising near-surface air temperatures, the influencing factors, the process of climate research and forecasting, and the possible ecological and social impacts of rising temperatures. For an overview of the public policy developments related to global warming occurring since the mid-20th century, see global warming policy . For a detailed description of Earth’s climate, its processes, and the responses of living things to its changing nature, see climate . For additional background on how Earth’s climate has changed throughout geologic time , see climatic variation and change . For a full description of Earth’s gaseous envelope, within which climate change and global warming occur, see atmosphere .

Compare-and-contrast reading on climate change

This morning George Will offered another in his series of reassuring columns about the "overstated" threat of climate change.  Today's version:

"When New York Times columnist Tom Friedman called upon 'young Americans' to 'get a million people on the Washington Mall calling for a price on carbon,' another columnist, Mark Steyn, responded : 'If you're 29, there has been no global warming for your entire adult life. If you're graduating high school, there has been no global warming since you entered first grade.' "Which could explain why the Mall does not reverberate with youthful clamors about carbon. And why, regarding climate change, the U.S. government, rushing to impose unilateral cap-and-trade burdens on the sagging U.S. economy, looks increasingly like someone who bought a closetful of platform shoes and bell-bottom slacks just as disco was dying."

Will presented the lack of youthful clamor as a sign of wholesome common sense. If you would like another way to think about the evidence, this one provided not by a columnist but by a physicist at UC Berkeley who has won a MacArthur grant, I recommend Richard A. Muller 's book Physics for Future Presidents . I happened to read most of it on a long plane flight yesterday, so I was all set for Will's column today. So you can be ready before his next one appears, I recommend ordering the book now.

Muller says that the evidence behind the hockey-stick chart is wrong. (Read it yourself to see why.) "In fact, much of what the public 'knows' about global warming is based on distortion, exaggeration, or cherry picking," he says, adding:

"An example of distortion is the melting of the Antarctic ice -- something that actually contradicts the global warming model but is presented as if it verifies them. Exaggeration includes the attribution of Hurricane Katrina to global warming, even though there is no scientific evidence that they are related.  Cherry picking is the process of selecting data that verify the global-warming hypothesis but ignoring data that contradict it."

The real purpose of his book is to set out as clearly as possible the way scientists approach the inevitably-conflicting evidence on big public policy issues like climate change (or the real risks of terrorism, or dealing with nuclear waste). Before the Iraq war, it would have been useful for intelligence officials to set out the way they balance their version of inevitably-conflicting and always-incomplete facts. Muller sets out the way climate scientists weigh the evidence pro and con concerning climate change and the probabilities for each explanation.

By the end of the process he has forcefully re-established the principle that real scientists view propositions as most convincing when all the doubts, caveats, and contrary bits of evidence are admitted -- whereas politicians and the public want to hear an all-or-nothing verdict with no hems or haws. Consistent with this approach, it is all the more powerful when Muller concludes that there really are reasons to worry about man-made climate change. He also provides guidelines about sensible and fanciful ways to deal with the problem. I am not equipped to judge this argument on purely scientific grounds; but the book is addressed to lay readers and is convincing in what it says about the process of scientific reasoning. If this latest George Will opus serves to drive readers to Muller's book, it will have done some good.

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10 (page 173) p. 173 Conclusion

• Published: November 2008
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The ‘Conclusion’ confirms that global warming is the major challenge for our global society. There is very little doubt that global warming will change our climate in the next century. So what are the solutions to global warming? First, there must be an international political solution. Second, funding for developing cheap and clean energy production must be increased, as all economic development is based on increasing energy usage. We must not pin all our hopes on global politics and clean energy technology, so we must prepare for the worst and adapt. If implemented now, a lot of the costs and damage that could be caused by changing climate can be mitigated.

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The Climate Change Debate: Man vs. Nature

The public discussion on climate change has become so polarized that some scientists don't even acknowledge there is a debate. Climate scientist at NASA 's Goddard Institute for Space Studies, Gavin Schmidt, is one of those people. "There aren't 'two sides' to the science, nor to the policy response," Schmidt said. "This implies that the whole thing is just a matter of an opinion – it is not." Another group of scientists would disagree with Schmidt. In June, the Sixth International Conference on Climate Change took place in Washington D.C. It was organized by The Heartland Institute, headquartered in Chicago, and its primary objective is to "dispute the claim that global warming is a crisis." In 2008, the organization published a report titled "Nature, Not Human Activity, Rules the Climate." Its president, Joseph Bast, talking to the journal Nature recently, discussed public opinion on climate change and the ongoing debate. "We've won the public opinion debate, and we've won the political debate as well," Bast said, "but the scientific debate is a source of enormous frustration." The climate change debate, as it discussed in the mainstream media, appears to be divided into two major sides. One side argues that the current global warming is caused by human factors while the other side insists it is occurring because of natural forces. In the latter argument, two natural causes that dominate the conversation are solar changes and changes to the Earth's orbit. [ 10 Surprising Results of Global Warming ] The Sun's Energy Scientists and astronomers have studied the impact of the Sun on the Earth's climate as far back as the early 1800s. Historians have traced the earliest such studies to the research of Sir William Herschel, who tried to link the frequency of sunspots to the price of wheat. His belief was that the number of sunspots would be indicative of the amount of the Sun's energy that is received by the Earth. That energy would affect the amount of wheat produced, which would affect the price.

Herschel’s study didn’t make a big impact at the time because he did not have access to historical temperature records to make any useful comparisons. However, there has been a significant amount of research conducted since then to show that variations in the Sun's energy output have an impact on changes in Earth’s climate.

A research study published earlier this year in the Journal of Atmospheric and Solar-Terrestrial Physics provides more evidence of this link between the Sun and the Earth. Through their analysis of historic temperature deviations, geomagnetic activity and the frequency of sunspots, the authors concluded that “the Sun has a significant role to play in the long-term and short-term climate change .” “With more and more data available, it may provoke some thought to further explore the solar influence on Earth's climate with geomagnetic activity acting as a possible link,” said lead author Mufti Sabi ud din, scientist of the Astrophysical Sciences Division at the Bhabha Atomic Research Center in India's Department of Atomic Energy. “It may evoke some response so as to bring to the fore the substantial role of the natural forcing at work on the observed climate variability.” Mufti, however, did note that the evidence of the Sun and other natural forces being the primary cause for climate change is still inadequate. “We do not rule out the natural forcings at work,” he said, “but there isn't enough quantitative evidence to say that natural forcings are the dominant cause of current climate change.” Pointing out the geopolitical sensitivity of the topic itself, Mufti was careful not to rule out anthropogenic effects.

“We have made it amply clear that the anthropogenic origins cannot also be ruled out,” Mufti said. According to Schmidt, while the Sun does have some impact, it is definitively not the reason for current patterns of climate change. “There is an effect,” Schmidt said, “but it is hard to detect in surface records, and is certainly not responsible for recent trends.” Orbital Change Another natural occurrence that has caused major changes in the Earth's climate in the past is shifts in the Earth's orbit. Consider the Sahara desert, for example. There is a wide acceptance among scientists that the Sahara transformed from a fertile grassland to a desert because of a change to the Earth's orbit. This shift in how the Earth circled the Sun affected the amount of sunlight that region of Africa received. The Earth's orbital tilt is said to vary between 22 and 25 degrees roughly every 41,000 years. While a natural event such as this could bring about major changes to the climate, some scientists are warning that there is a possibility for reverse feedback. In other words, instead of an orbital tilt causing climate change, such as the one that took place in the African continent, current changes in climate could end up causing changes in the Earth's axial tilt. In an article published late last year, Astrobiology Magazine reported on such a prediction: “Scientists from NASA's Jet Propulsion Laboratory say that the current melting of ice in Greenland is already causing the tilt to change at a rate of approximately 2.6 centimeters each year. They predict that his change could increase in the years ahead.” The Politics of Climate

Hundreds of scientists around the world have conducted research that show human activities contribute the most to today’s climate change. We are changing the Earth’s atmosphere by emitting huge amounts of greenhouse gases such as carbon dioxide, most of which comes from the burning of fossil fuels. Other human activities include agriculture and changes in land-use patterns. They all work to tip the Earth’s energy balance by trapping more heat. Even scientists who think human activity is the main cause of climate change don't deny that natural changes will cause temperature fluctuations on Earth. However, their argument is that in the current cycle of climate change, the impact caused by man is far greater. But there’s no indication that the two sides of the climate change debate will reach any common ground in the near future on what scientific evidence is showing, or what policy decisions should be adopted. Perhaps the most well-known spokesperson for climate change, former U.S. Vice President Al Gore, recently attracted a lot of media attention for his emotional rant against climate skeptics. When he spoke at the Aspen Institution in Boulder, Colorado in early August, he compared climate skeptics to those who argued that smoking was not harmful to human health in the 1960s. "There are about 10 other memes that are out there, and when you go and talk to any audience about climate, you hear them washing back at you the same crap, over and over and over again,” Gore said. “There is no longer shared reality on an issue like climate, even though the very existence of our civilization is threatened." Although the climate scientists who say that the climate is changing (about 97 percent by some estimates) far outnumber those who don’t, Gore's comments indicate the strength of the message of those who argue against climate change.

The Brookings Institute released a report in April on the public opinion on climate change in the United States and Canada. In a survey of 2,130 people, the report found that there is a progressive decrease in the number of people who think there is “solid evidence of global warming” and an increase in the number who think there is no solid evidence. In the fall of 2008, 17 percent of people did not believe in global warming. In the fall of 2010, that number had increased to 26 percent. Even though the number of climate change believers has decreased, the majority of people still believed that the Earth is undergoing global warming and most of them (61 percent of Americans and 57 percent of Canadians) felt it was a “very serious” problem. Moving On Despite knowing the difference between weather and climate, both climate supporters and opponents, usually in politics and media, often can't refrain from using short-term weather patterns to bolster their respective arguments. Harsh winters are used as evidence of no global warming while scorching summers are used to support the viewpoint of human-caused warming of the Earth. Individual seasonal weather events such as a “snowmageddon” or heat waves cannot be directly attributed to either argument of the climate change debate because such events alone are temporary affects. Climate change, on the other hand, is a long-term problem. However, an increasing frequency of such extreme weather events can be another indication that climate change is in fact a reality. In this complex and seemingly never-ending debate, there is now an increasing number of scientists and other observers who say researchers and policymakers need to move on, to respond to the Earth's reactions to global warming instead of still debating whether or not it is a reality.

Climate change effects nearly every other sector of society. Take, for example, public health. Some of the diseases that impact global populations the most, such as malaria and diarrhea that kill millions each year, are highly sensitive to climatic conditions. Then there is the inequity of these risks. China is now the world’s top emitter of greenhouse gases, but developed countries, primarily the United States, is still mainly responsible for causing climate change after having emitted the most pollution for the longest time. But the populations that suffer the most from climatic changes will be those in developing countries – countries that have contributed the least to climate change and populations who have the least access to resources that could help them deal with the consequences. There are numerous other reports which show the impact of climate change on various other sectors such as agriculture, energy, insurance and even national security. Schmidt expressed the urgency of addressing climate change now. "The consequences of climate change increase, and they increase quite rapidly as the temperatures rise," Schmidt said. "The faster we act, the less bad the peak warming will be. It will take a long time to turn this around." But Schmidt rejects the idea that there is a point of no return. "This idea that there's just one point, I think that makes people complacent now and then it would make people fatalistic afterwards," Schmidt said. "Whatever the situation is, there will be choices that we can make as a society that will make it better in the future or worse. The longer we let it go without doing anything, the worse the consequences will be before it comes back down and we get it back under control, but there's never a point at which there's nothing that can be done. There is an urgency to acting but it's not because there's a point of no return."

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This story was provided by Astrobiology Magazine , a web-based publication sponsored by the NASA astrobiology program .

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• Biology Article
• Essay on Global Warming

Essay On Global Warming

Essay on global warming is an important topic for students to understand. The essay brings to light the plight of the environment and the repercussion of anthropogenic activities. Continue reading to discover tips and tricks for writing an engaging and interesting essay on global warming.

Essay On Global Warming in 300 Words

Global warming is a phenomenon where the earth’s average temperature rises due to increased amounts of greenhouse gases. Greenhouse gases such as carbon dioxide, methane and ozone trap the incoming radiation from the sun. This effect creates a natural “blanket”, which prevents the heat from escaping back into the atmosphere. This effect is called the greenhouse effect.

Contrary to popular belief, greenhouse gases are not inherently bad. In fact, the greenhouse effect is quite important for life on earth. Without this effect, the sun’s radiation would be reflected back into the atmosphere, freezing the surface and making life impossible. However, when greenhouse gases in excess amounts get trapped, serious repercussions begin to appear. The polar ice caps begin to melt, leading to a rise in sea levels. Furthermore, the greenhouse effect is accelerated when polar ice caps and sea ice melts. This is due to the fact the ice reflects 50% to 70% of the sun’s rays back into space, but without ice, the solar radiation gets absorbed. Seawater reflects only 6% of the sun’s radiation back into space. What’s more frightening is the fact that the poles contain large amounts of carbon dioxide trapped within the ice. If this ice melts, it will significantly contribute to global warming. 

A related scenario when this phenomenon goes out of control is the runaway-greenhouse effect. This scenario is essentially similar to an apocalypse, but it is all too real. Though this has never happened in the earth’s entire history, it is speculated to have occurred on Venus. Millions of years ago, Venus was thought to have an atmosphere similar to that of the earth. But due to the runaway greenhouse effect, surface temperatures around the planet began rising. 

If this occurs on the earth, the runaway greenhouse effect will lead to many unpleasant scenarios – temperatures will rise hot enough for oceans to evaporate. Once the oceans evaporate, the rocks will start to sublimate under heat. In order to prevent such a scenario, proper measures have to be taken to stop climate change.

More to Read: Learn How Greenhouse Effect works

Tips To Writing the Perfect Essay

Consider adopting the following strategies when writing an essay. These are proven methods of securing more marks in an exam or assignment.

• Begin the essay with an introductory paragraph detailing the history or origin of the given topic.
• Try to reduce the use of jargons. Use sparingly if the topic requires it.
• Ensure that the content is presented in bulleted points wherever appropriate.
• Insert and highlight factual data, such as dates, names and places.
• Remember to break up the content into smaller paragraphs. 100-120 words per paragraph should suffice.
• Always conclude the essay with a closing paragraph.

Explore more essays on biology or other related fields at BYJU’S.

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Sample essay on global warming

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Essay on Global Warming

• Updated on  
• Apr 27, 2024

Being able to write an essay is an integral part of mastering any language. Essays form an integral part of many academic and scholastic exams like the SAT, and UPSC amongst many others. It is a crucial evaluative part of English proficiency tests as well like IELTS, TOEFL, etc. Major essays are meant to emphasize public issues of concern that can have significant consequences on the world. To understand the concept of Global Warming and its causes and effects, we must first examine the many factors that influence the planet’s temperature and what this implies for the world’s future. Here’s an unbiased look at the essay on Global Warming and other essential related topics.

Short Essay on Global Warming and Climate Change?

Since the industrial and scientific revolutions, Earth’s resources have been gradually depleted. Furthermore, the start of the world’s population’s exponential expansion is particularly hard on the environment. Simply put, as the population’s need for consumption grows, so does the use of natural resources , as well as the waste generated by that consumption.

Climate change has been one of the most significant long-term consequences of this. Climate change is more than just the rise or fall of global temperatures; it also affects rain cycles, wind patterns, cyclone frequencies, sea levels, and other factors. It has an impact on all major life groupings on the planet.

Also Read: Essay on Yoga Day

Also Read: Speech on Yoga Day

What is Global Warming?

Global warming is the unusually rapid increase in Earth’s average surface temperature over the past century, primarily due to the greenhouse gases released by people burning fossil fuels . The greenhouse gases consist of methane, nitrous oxide, ozone, carbon dioxide, water vapour, and chlorofluorocarbons. The weather prediction has been becoming more complex with every passing year, with seasons more indistinguishable, and the general temperatures hotter.

The number of hurricanes, cyclones, droughts, floods, etc., has risen steadily since the onset of the 21st century. The supervillain behind all these changes is Global Warming. The name is quite self-explanatory; it means the rise in the temperature of the Earth.

Also Read: What is a Natural Disaster?

What are the Causes of Global Warming?

According to recent studies, many scientists believe the following are the primary four causes of global warming:

• Deforestation 
• Greenhouse emissions
• Carbon emissions per capita

Extreme global warming is causing natural disasters , which can be seen all around us. One of the causes of global warming is the extreme release of greenhouse gases that become trapped on the earth’s surface, causing the temperature to rise. Similarly, volcanoes contribute to global warming by spewing excessive CO2 into the atmosphere.

The increase in population is one of the major causes of Global Warming. This increase in population also leads to increased air pollution . Automobiles emit a lot of CO2, which remains in the atmosphere. This increase in population is also causing deforestation, which contributes to global warming.

The earth’s surface emits energy into the atmosphere in the form of heat, keeping the balance with the incoming energy. Global warming depletes the ozone layer, bringing about the end of the world. There is a clear indication that increased global warming will result in the extinction of all life on Earth’s surface.

Also Read: Land, Soil, Water, Natural Vegetation, and Wildlife Resources

Solutions for Global Warming

Of course, industries and multinational conglomerates emit more carbon than the average citizen. Nonetheless, activism and community effort are the only viable ways to slow the worsening effects of global warming. Furthermore, at the state or government level, world leaders must develop concrete plans and step-by-step programmes to ensure that no further harm is done to the environment in general.

Although we are almost too late to slow the rate of global warming, finding the right solution is critical. Everyone, from individuals to governments, must work together to find a solution to Global Warming. Some of the factors to consider are pollution control, population growth, and the use of natural resources.

One very important contribution you can make is to reduce your use of plastic. Plastic is the primary cause of global warming, and recycling it takes years. Another factor to consider is deforestation, which will aid in the control of global warming. More tree planting should be encouraged to green the environment. Certain rules should also govern industrialization. Building industries in green zones that affect plants and species should be prohibited.

Also Read: Essay on Pollution

Effects of Global Warming

Global warming is a real problem that many people want to disprove to gain political advantage. However, as global citizens, we must ensure that only the truth is presented in the media.

This decade has seen a significant impact from global warming. The two most common phenomena observed are glacier retreat and arctic shrinkage. Glaciers are rapidly melting. These are clear manifestations of climate change.

Another significant effect of global warming is the rise in sea level. Flooding is occurring in low-lying areas as a result of sea-level rise. Many countries have experienced extreme weather conditions. Every year, we have unusually heavy rain, extreme heat and cold, wildfires, and other natural disasters.

Similarly, as global warming continues, marine life is being severely impacted. This is causing the extinction of marine species as well as other problems. Furthermore, changes are expected in coral reefs, which will face extinction in the coming years. These effects will intensify in the coming years, effectively halting species expansion. Furthermore, humans will eventually feel the negative effects of Global Warming.

Also Read: Concept of Sustainable Development

Sample Essays on Global Warming

Here are some sample essays on Global Warming:

Essay on Global Warming Paragraph in 100 – 150 words

Global Warming is caused by the increase of carbon dioxide levels in the earth’s atmosphere and is a result of human activities that have been causing harm to our environment for the past few centuries now. Global Warming is something that can’t be ignored and steps have to be taken to tackle the situation globally. The average temperature is constantly rising by 1.5 degrees Celsius over the last few years.

The best method to prevent future damage to the earth, cutting down more forests should be banned and Afforestation should be encouraged. Start by planting trees near your homes and offices, participate in events, and teach the importance of planting trees. It is impossible to undo the damage but it is possible to stop further harm.

Also Read: Social Forestry

Essay on Global Warming in 250 Words

Over a long period, it is observed that the temperature of the earth is increasing. This affected wildlife, animals, humans, and every living organism on earth. Glaciers have been melting, and many countries have started water shortages, flooding, and erosion and all this is because of global warming. 

No one can be blamed for global warming except for humans. Human activities such as gases released from power plants, transportation, and deforestation have increased gases such as carbon dioxide, CFCs, and other pollutants in the earth’s atmosphere.                                              The main question is how can we control the current situation and build a better world for future generations. It starts with little steps by every individual. 

Start using cloth bags made from sustainable materials for all shopping purposes, instead of using high-watt lights use energy-efficient bulbs, switch off the electricity, don’t waste water, abolish deforestation and encourage planting more trees. Shift the use of energy from petroleum or other fossil fuels to wind and solar energy. Instead of throwing out the old clothes donate them to someone so that it is recycled. 

Donate old books, don’t waste paper.  Above all, spread awareness about global warming. Every little thing a person does towards saving the earth will contribute in big or small amounts. We must learn that 1% effort is better than no effort. Pledge to take care of Mother Nature and speak up about global warming.

Also Read: Types of Water Pollution

Essay on Global Warming in 500 Words

Global warming isn’t a prediction, it is happening! A person denying it or unaware of it is in the most simple terms complicit. Do we have another planet to live on? Unfortunately, we have been bestowed with this one planet only that can sustain life yet over the years we have turned a blind eye to the plight it is in. Global warming is not an abstract concept but a global phenomenon occurring ever so slowly even at this moment. Global Warming is a phenomenon that is occurring every minute resulting in a gradual increase in the Earth’s overall climate. Brought about by greenhouse gases that trap the solar radiation in the atmosphere, global warming can change the entire map of the earth, displacing areas, flooding many countries, and destroying multiple lifeforms. Extreme weather is a direct consequence of global warming but it is not an exhaustive consequence. There are virtually limitless effects of global warming which are all harmful to life on earth. The sea level is increasing by 0.12 inches per year worldwide. This is happening because of the melting of polar ice caps because of global warming. This has increased the frequency of floods in many lowland areas and has caused damage to coral reefs. The Arctic is one of the worst-hit areas affected by global warming. Air quality has been adversely affected and the acidity of the seawater has also increased causing severe damage to marine life forms. Severe natural disasters are brought about by global warming which has had dire effects on life and property. As long as mankind produces greenhouse gases, global warming will continue to accelerate. The consequences are felt at a much smaller scale which will increase to become drastic shortly. The power to save the day lies in the hands of humans, the need is to seize the day. Energy consumption should be reduced on an individual basis. Fuel-efficient cars and other electronics should be encouraged to reduce the wastage of energy sources. This will also improve air quality and reduce the concentration of greenhouse gases in the atmosphere. Global warming is an evil that can only be defeated when fought together. It is better late than never. If we all take steps today, we will have a much brighter future tomorrow. Global warming is the bane of our existence and various policies have come up worldwide to fight it but that is not enough. The actual difference is made when we work at an individual level to fight it. Understanding its import now is crucial before it becomes an irrevocable mistake. Exterminating global warming is of utmost importance and each one of us is as responsible for it as the next.  

Also Read: Essay on Library: 100, 200 and 250 Words

Essay on Global Warming UPSC

Always hear about global warming everywhere, but do we know what it is? The evil of the worst form, global warming is a phenomenon that can affect life more fatally. Global warming refers to the increase in the earth’s temperature as a result of various human activities. The planet is gradually getting hotter and threatening the existence of lifeforms on it. Despite being relentlessly studied and researched, global warming for the majority of the population remains an abstract concept of science. It is this concept that over the years has culminated in making global warming a stark reality and not a concept covered in books. Global warming is not caused by one sole reason that can be curbed. Multifarious factors cause global warming most of which are a part of an individual’s daily existence. Burning of fuels for cooking, in vehicles, and for other conventional uses, a large amount of greenhouse gases like carbon dioxide, and methane amongst many others is produced which accelerates global warming. Rampant deforestation also results in global warming as lesser green cover results in an increased presence of carbon dioxide in the atmosphere which is a greenhouse gas.  Finding a solution to global warming is of immediate importance. Global warming is a phenomenon that has to be fought unitedly. Planting more trees can be the first step that can be taken toward warding off the severe consequences of global warming. Increasing the green cover will result in regulating the carbon cycle. There should be a shift from using nonrenewable energy to renewable energy such as wind or solar energy which causes less pollution and thereby hinder the acceleration of global warming. Reducing energy needs at an individual level and not wasting energy in any form is the most important step to be taken against global warming. The warning bells are tolling to awaken us from the deep slumber of complacency we have slipped into. Humans can fight against nature and it is high time we acknowledged that. With all our scientific progress and technological inventions, fighting off the negative effects of global warming is implausible. We have to remember that we do not inherit the earth from our ancestors but borrow it from our future generations and the responsibility lies on our shoulders to bequeath them a healthy planet for life to exist. 

Also Read: Essay on Disaster Management

Climate Change and Global Warming Essay

Global Warming and Climate Change are two sides of the same coin. Both are interrelated with each other and are two issues of major concern worldwide. Greenhouse gases released such as carbon dioxide, CFCs, and other pollutants in the earth’s atmosphere cause Global Warming which leads to climate change. Black holes have started to form in the ozone layer that protects the earth from harmful ultraviolet rays. 

Human activities have created climate change and global warming. Industrial waste and fumes are the major contributors to global warming. 

Another factor affecting is the burning of fossil fuels, deforestation and also one of the reasons for climate change.  Global warming has resulted in shrinking mountain glaciers in Antarctica, Greenland, and the Arctic and causing climate change. Switching from the use of fossil fuels to energy sources like wind and solar. 

When buying any electronic appliance buy the best quality with energy savings stars. Don’t waste water and encourage rainwater harvesting in your community. 

Also Read: Essay on Air Pollution

Tips to Write an Essay

Writing an effective essay needs skills that few people possess and even fewer know how to implement. While writing an essay can be an assiduous task that can be unnerving at times, some key pointers can be inculcated to draft a successful essay. These involve focusing on the structure of the essay, planning it out well, and emphasizing crucial details.

Mentioned below are some pointers that can help you write better structure and more thoughtful essays that will get across to your readers:

• Prepare an outline for the essay to ensure continuity and relevance and no break in the structure of the essay
• Decide on a thesis statement that will form the basis of your essay. It will be the point of your essay and help readers understand your contention
• Follow the structure of an introduction, a detailed body followed by a conclusion so that the readers can comprehend the essay in a particular manner without any dissonance.
• Make your beginning catchy and include solutions in your conclusion to make the essay insightful and lucrative to read
• Reread before putting it out and add your flair to the essay to make it more personal and thereby unique and intriguing for readers  

Also Read: I Love My India Essay: 100 and 500+ Words in English for School Students

Ans. Both natural and man-made factors contribute to global warming. The natural one also contains methane gas, volcanic eruptions, and greenhouse gases. Deforestation, mining, livestock raising, burning fossil fuels, and other man-made causes are next.

Ans. The government and the general public can work together to stop global warming. Trees must be planted more often, and deforestation must be prohibited. Auto usage needs to be curbed, and recycling needs to be promoted.

Ans. Switching to renewable energy sources , adopting sustainable farming, transportation, and energy methods, and conserving water and other natural resources.

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Digvijay Singh

Having 2+ years of experience in educational content writing, withholding a Bachelor's in Physical Education and Sports Science and a strong interest in writing educational content for students enrolled in domestic and foreign study abroad programmes. I believe in offering a distinct viewpoint to the table, to help students deal with the complexities of both domestic and foreign educational systems. Through engaging storytelling and insightful analysis, I aim to inspire my readers to embark on their educational journeys, whether abroad or at home, and to make the most of every learning opportunity that comes their way.

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This was really a good essay on global warming… There has been used many unic words..and I really liked it!!!Seriously I had been looking for a essay about Global warming just like this…

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I want to learn how to write essay writing so I joined this page.This page is very useful for everyone.

Hi, we are glad that we could help you to write essays. We have a beginner’s guide to write essays ( https://leverageedu.com/blog/essay-writing/ ) and we think this might help you.

It is not good , to have global warming in our earth .So we all have to afforestation program on all the world.

thank you so much

Very educative , helpful and it is really going to strength my English knowledge to structure my essay in future

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Global warming is the increase in 𝓽𝓱𝓮 ᴀᴠᴇʀᴀɢᴇ ᴛᴇᴍᴘᴇʀᴀᴛᴜʀᴇs ᴏғ ᴇᴀʀᴛʜ🌎 ᴀᴛᴍᴏsᴘʜᴇʀᴇ

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What Are the Causes of Climate Change?

We can’t fight climate change without understanding what drives it.

Low water levels at Shasta Lake, California, following a historic drought in October 2021

Andrew Innerarity/California Department of Water Resources

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At the root of climate change is the phenomenon known as the greenhouse effect , the term scientists use to describe the way that certain atmospheric gases “trap” heat that would otherwise radiate upward, from the planet’s surface, into outer space. On the one hand, we have the greenhouse effect to thank for the presence of life on earth; without it, our planet would be cold and unlivable.

But beginning in the mid- to late-19th century, human activity began pushing the greenhouse effect to new levels. The result? A planet that’s warmer right now than at any other point in human history, and getting ever warmer. This global warming has, in turn, dramatically altered natural cycles and weather patterns, with impacts that include extreme heat, protracted drought, increased flooding, more intense storms, and rising sea levels. Taken together, these miserable and sometimes deadly effects are what have come to be known as climate change .

Detailing and discussing the human causes of climate change isn’t about shaming people, or trying to make them feel guilty for their choices. It’s about defining the problem so that we can arrive at effective solutions. And we must honestly address its origins—even though it can sometimes be difficult, or even uncomfortable, to do so. Human civilization has made extraordinary productivity leaps, some of which have led to our currently overheated planet. But by harnessing that same ability to innovate and attaching it to a renewed sense of shared responsibility, we can find ways to cool the planet down, fight climate change , and chart a course toward a more just, equitable, and sustainable future.

Here’s a rough breakdown of the factors that are driving climate change.

Natural causes of climate change

Human-driven causes of climate change, transportation, electricity generation, industry & manufacturing, agriculture, oil & gas development, deforestation, our lifestyle choices.

Some amount of climate change can be attributed to natural phenomena. Over the course of Earth’s existence, volcanic eruptions , fluctuations in solar radiation , tectonic shifts , and even small changes in our orbit have all had observable effects on planetary warming and cooling patterns.

But climate records are able to show that today’s global warming—particularly what has occured since the start of the industrial revolution—is happening much, much faster than ever before. According to NASA , “[t]hese natural causes are still in play today, but their influence is too small or they occur too slowly to explain the rapid warming seen in recent decades.” And the records refute the misinformation that natural causes are the main culprits behind climate change, as some in the fossil fuel industry and conservative think tanks would like us to believe.

Chemical manufacturing plants emit fumes along Onondaga Lake in Solvay, New York, in the late-19th century. Over time, industrial development severely polluted the local area.

Library of Congress, Prints & Photographs Division, Detroit Publishing Company Collection

Scientists agree that human activity is the primary driver of what we’re seeing now worldwide. (This type of climate change is sometimes referred to as anthropogenic , which is just a way of saying “caused by human beings.”) The unchecked burning of fossil fuels over the past 150 years has drastically increased the presence of atmospheric greenhouse gases, most notably carbon dioxide . At the same time, logging and development have led to the widespread destruction of forests, wetlands, and other carbon sinks —natural resources that store carbon dioxide and prevent it from being released into the atmosphere.

Right now, atmospheric concentrations of greenhouse gases like carbon dioxide, methane , and nitrous oxide are the highest they’ve been in the last 800,000 years . Some greenhouse gases, like hydrochlorofluorocarbons (HFCs) , do not even exist in nature. By continuously pumping these gases into the air, we helped raise the earth’s average temperature by about 1.9 degrees Fahrenheit during the 20th century—which has brought us to our current era of deadly, and increasingly routine, weather extremes. And it’s important to note that while climate change affects everyone in some way, it doesn’t do so equally: All over the world, people of color and those living in economically disadvantaged or politically marginalized communities bear a much larger burden , despite the fact that these communities play a much smaller role in warming the planet.

Our ways of generating power for electricity, heat, and transportation, our built environment and industries, our ways of interacting with the land, and our consumption habits together serve as the primary drivers of climate change. While the percentages of greenhouse gases stemming from each source may fluctuate, the sources themselves remain relatively consistent.

Traffic on Interstate 25 in Denver

David Parsons/iStock

The cars, trucks, ships, and planes that we use to transport ourselves and our goods are a major source of global greenhouse gas emissions. (In the United States, they actually constitute the single-largest source.) Burning petroleum-based fuel in combustion engines releases massive amounts of carbon dioxide into the atmosphere. Passenger cars account for 41 percent of those emissions, with the typical passenger vehicle emitting about 4.6 metric tons of carbon dioxide per year. And trucks are by far the worst polluters on the road. They run almost constantly and largely burn diesel fuel, which is why, despite accounting for just 4 percent of U.S. vehicles, trucks emit 23 percent of all greenhouse gas emissions from transportation.

We can get these numbers down, but we need large-scale investments to get more zero-emission vehicles on the road and increase access to reliable public transit .

As of 2021, nearly 60 percent of the electricity used in the United States comes from the burning of coal, natural gas , and other fossil fuels . Because of the electricity sector’s historical investment in these dirty energy sources, it accounts for roughly a quarter of U.S. greenhouse gas emissions, including carbon dioxide, methane, and nitrous oxide.

That history is undergoing a major change, however: As renewable energy sources like wind and solar become cheaper and easier to develop, utilities are turning to them more frequently. The percentage of clean, renewable energy is growing every year—and with that growth comes a corresponding decrease in pollutants.

But while things are moving in the right direction, they’re not moving fast enough. If we’re to keep the earth’s average temperature from rising more than 1.5 degrees Celsius, which scientists say we must do in order to avoid the very worst impacts of climate change, we have to take every available opportunity to speed up the shift from fossil fuels to renewables in the electricity sector.

The factories and facilities that produce our goods are significant sources of greenhouse gases; in 2020, they were responsible for fully 24 percent of U.S. emissions. Most industrial emissions come from the production of a small set of carbon-intensive products, including basic chemicals, iron and steel, cement and concrete, aluminum, glass, and paper. To manufacture the building blocks of our infrastructure and the vast array of products demanded by consumers, producers must burn through massive amounts of energy. In addition, older facilities in need of efficiency upgrades frequently leak these gases, along with other harmful forms of air pollution .

One way to reduce the industrial sector’s carbon footprint is to increase efficiency through improved technology and stronger enforcement of pollution regulations. Another way is to rethink our attitudes toward consumption (particularly when it comes to plastics ), recycling , and reuse —so that we don’t need to be producing so many things in the first place. And, since major infrastructure projects rely heavily on industries like cement manufacturing (responsible for 7 percent of annual global greenhouse gas), policy mandates must leverage the government’s purchasing power to grow markets for cleaner alternatives, and ensure that state and federal agencies procure more sustainably produced materials for these projects. Hastening the switch from fossil fuels to renewables will also go a long way toward cleaning up this energy-intensive sector.

The advent of modern, industrialized agriculture has significantly altered the vital but delicate relationship between soil and the climate—so much so that agriculture accounted for 11 percent of U.S. greenhouse gas emissions in 2020. This sector is especially notorious for giving off large amounts of nitrous oxide and methane, powerful gases that are highly effective at trapping heat. The widespread adoption of chemical fertilizers , combined with certain crop-management practices that prioritize high yields over soil health, means that agriculture accounts for nearly three-quarters of the nitrous oxide found in our atmosphere. Meanwhile, large-scale industrialized livestock production continues to be a significant source of atmospheric methane, which is emitted as a function of the digestive processes of cattle and other ruminants.

Stephen McComber holds a squash harvested from the community garden in Kahnawà:ke Mohawk Territory, a First Nations reserve of the Mohawks of Kahnawà:ke, in Quebec.

Stephanie Foden for NRDC

But farmers and ranchers—especially Indigenous farmers, who have been tending the land according to sustainable principles —are reminding us that there’s more than one way to feed the world. By adopting the philosophies and methods associated with regenerative agriculture , we can slash emissions from this sector while boosting our soil’s capacity for sequestering carbon from the atmosphere, and producing healthier foods.

A decades-old, plugged and abandoned oil well at a cattle ranch in Crane County, Texas, in June 2021, when it was found to be leaking brine water

Matthew Busch/Bloomberg via Getty Images

Oil and gas lead to emissions at every stage of their production and consumption—not only when they’re burned as fuel, but just as soon as we drill a hole in the ground to begin extracting them. Fossil fuel development is a major source of methane, which invariably leaks from oil and gas operations : drilling, fracking , transporting, and refining. And while methane isn’t as prevalent a greenhouse gas as carbon dioxide, it’s many times more potent at trapping heat during the first 20 years of its release into the atmosphere. Even abandoned and inoperative wells—sometimes known as “orphaned” wells —leak methane. More than 3 million of these old, defunct wells are spread across the country and were responsible for emitting more than 280,000 metric tons of methane in 2018.

Unsurprisingly, given how much time we spend inside of them, our buildings—both residential and commercial—emit a lot of greenhouse gases. Heating, cooling, cooking, running appliances, and maintaining other building-wide systems accounted for 13 percent of U.S. emissions overall in 2020. And even worse, some 30 percent of the energy used in U.S. buildings goes to waste, on average.

Every day, great strides are being made in energy efficiency , allowing us to achieve the same (or even better) results with less energy expended. By requiring all new buildings to employ the highest efficiency standards—and by retrofitting existing buildings with the most up-to-date technologies—we’ll reduce emissions in this sector while simultaneously making it easier and cheaper for people in all communities to heat, cool, and power their homes: a top goal of the environmental justice movement.

An aerial view of clearcut sections of boreal forest near Dryden in Northwestern Ontario, Canada, in June 2019

River Jordan for NRDC

Another way we’re injecting more greenhouse gas into the atmosphere is through the clearcutting of the world’s forests and the degradation of its wetlands . Vegetation and soil store carbon by keeping it at ground level or underground. Through logging and other forms of development, we’re cutting down or digging up vegetative biomass and releasing all of its stored carbon into the air. In Canada’s boreal forest alone, clearcutting is responsible for releasing more than 25 million metric tons of carbon dioxide into the atmosphere each year—the emissions equivalent of 5.5 million vehicles.

Government policies that emphasize sustainable practices, combined with shifts in consumer behavior , are needed to offset this dynamic and restore the planet’s carbon sinks .

The Yellow Line Metro train crossing over the Potomac River from Washington, DC, to Virginia on June 24, 2022

Sarah Baker

The decisions we make every day as individuals—which products we purchase, how much electricity we consume, how we get around, what we eat (and what we don’t—food waste makes up 4 percent of total U.S. greenhouse gas emissions)—add up to our single, unique carbon footprints . Put all of them together and you end up with humanity’s collective carbon footprint. The first step in reducing it is for us to acknowledge the uneven distribution of climate change’s causes and effects, and for those who bear the greatest responsibility for global greenhouse gas emissions to slash them without bringing further harm to those who are least responsible .

The big, climate-affecting decisions made by utilities, industries, and governments are shaped, in the end, by us : our needs, our demands, our priorities. Winning the fight against climate change will require us to rethink those needs, ramp up those demands , and reset those priorities. Short-term thinking of the sort that enriches corporations must give way to long-term planning that strengthens communities and secures the health and safety of all people. And our definition of climate advocacy must go beyond slogans and move, swiftly, into the realm of collective action—fueled by righteous anger, perhaps, but guided by faith in science and in our ability to change the world for the better.

If our activity has brought us to this dangerous point in human history, breaking old patterns can help us find a way out.

This NRDC.org story is available for online republication by news media outlets or nonprofits under these conditions: The writer(s) must be credited with a byline; you must note prominently that the story was originally published by NRDC.org and link to the original; the story cannot be edited (beyond simple things such as grammar); you can’t resell the story in any form or grant republishing rights to other outlets; you can’t republish our material wholesale or automatically—you need to select stories individually; you can’t republish the photos or graphics on our site without specific permission; you should drop us a note to let us know when you’ve used one of our stories.

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Home / Global Warming’s Six Audiences: A cross-national comparison in nearly 200 countries and territories worldwide

Climate Note · Aug 1, 2023

Global warming’s six audiences: a cross-national comparison in nearly 200 countries and territories worldwide, by marija verner , jennifer marlon , jennifer carman , seth rosenthal , matthew ballew , anthony leiserowitz , nicole buttermore and kelsey mulcahy, filed under: audiences and beliefs & attitudes.

In March and April 2022, the Yale Program on Climate Change Communication (YPCCC) conducted an international survey in collaboration with Data for Good at Meta to examine public climate change knowledge, attitudes, policy preferences, and behavior among Facebook users in nearly 200 countries and territories worldwide.

Prior research by YPCCC and the George Mason University Center for Climate Change Communication has found that people in the United States can be categorized into six distinct groups – Alarmed, Concerned, Cautious, Disengaged, Doubtful, and Dismissive – based on their beliefs and attitudes about climate change ( Global Warming’s Six Americas ).

The Alarmed are convinced climate change is happening, human-caused, and an urgent threat, and strongly support climate policies. The Concerned think human-caused climate change is happening and is a serious threat, and support climate policies. However, they tend to believe that climate impacts are still distant in time and space, thus the issue remains a lower priority. The Cautious have not yet made up their minds: Is climate change happening? Is it human-caused? Is it serious? The Disengaged know little to nothing about climate change and rarely if ever hear about it. The Doubtful do not think climate change is happening or believe it is just a natural cycle. And the Dismissive are convinced climate change is not happening, human-caused, or a threat, and oppose most climate policies.

The international survey conducted by YPCCC and Data for Good at Meta included the Six Americas Super Short Survey (SASSY), a tool that categorizes respondents into this six audiences framework with just 4 questions. Ideally, one would conduct an in-depth study to develop a tailored segmentation of climate change audiences within each country. However, the Six-Audiences framework and SASSY tool can be used as a first-order approximation and a means of cross-national comparison using an identical set of questions that are relevant in all national contexts.

We find that the Alarmed are the largest group in about three-fourths (80 of the 110) of the countries and territories surveyed. In fact, half or more respondents in twenty-nine countries and territories are Alarmed: the five countries with the largest percentage of Alarmed are Chile (65%), Mexico (64%), Malawi (63%), Bolivia (62%), and Sri Lanka (61%). Czechia and Yemen have the smallest percentages of Alarmed (both 9%). In the United States, about one-third of respondents are Alarmed (34%).

By contrast, relatively few respondents in any country or territory are Doubtful or Dismissive. Among major emitters, the United States has the largest proportion of Doubtful and Dismissive, more than one in five (22%).

The United States is less Alarmed about global warming than most other top carbon-emitting countries

There are substantial differences among the 15 nations responsible for the largest annual shares of global carbon emissions ( this study did not include China, Russia, or Iran ). Among these countries, the largest proportion of Alarmed are in Mexico (64%), followed by Brazil (59%), and India (55%).

The United States is the second largest annual producer of the carbon emissions that cause global warming. Yet, relatively few people in the United States are Alarmed about global warming, compared to other top emitters. The U.S. and Germany have the fourth-smallest percentage of Alarmed (34%), after the United Kingdom (31%), Saudi Arabia (29%), and Indonesia (27%). On the other end of the Six Audiences spectrum, the countries with the largest percentages of Doubtful or Dismissive respondents are the United States (22%), Saudi Arabia (17%), and Australia (16%).

The Six Audiences by Region

The following charts contain results categorized by region. Among countries in Asia and the Pacific, Sri Lanka has the largest proportion of Alarmed (61%), while Thailand has the smallest (26%). Australia and New Zealand have the largest proportions of Doubtful or Dismissive respondents at 16% and 13% respectively.

Among European countries, Portugal has the largest proportion of Alarmed (56%), while Czechia has the smallest (9%). European countries where more than 10% of respondents are either Doubtful or Dismissive include: Norway (23%), Finland (19%), Kosovo (19%), the Netherlands (19%), Czechia (17%), Sweden (14%), Cyprus (12%), Armenia (11%), Denmark (11%), Germany (11%), the United Kingdom (11%), Bosnia and Herzegovina (10%), Ireland (10%), and Romania (10%).

In North America, Mexico has the largest percentage of Alarmed respondents and is among the countries with the highest percentage globally (64%). Majorities of respondents are also Alarmed in Costa Rica (62%), El Salvador (60%), Puerto Rico (60%), Panama (58%), Nicaragua (57%), Guatemala (54%), and Honduras (54%). By contrast, Haiti has the smallest percentage of Alarmed respondents in North America (32%). Countries with relatively large proportions of Doubtful or Dismissive respondents are the United States (22%), Haiti (15%), and Canada (12%).

Compared to other regions, South America has the greatest proportion of countries (6 out of 9) with a majority of Alarmed respondents. Chile has the largest proportion of Alarmed respondents (65%), while Uruguay has the smallest (43%). Very few people in South America are either Doubtful or Dismissive (7% or fewer in all countries) . 

In the region of Southwest Asia and North Africa, Turkey is the only country where about half of respondents are Alarmed (51%). In contrast, only 9% of respondents in Yemen are Alarmed. Most countries in this region have over 10% of respondents who are Doubtful or Dismissive, with especially large percentages in Yemen (34%), Jordan (27%), and Iraq (25%).

In Sub-Saharan Africa, Malawi has the largest percentage of Alarmed respondents (63%). Conversely, Nigeria – Africa’s top oil producer – has the smallest proportion of Alarmed respondents, roughly one in three (34%). Countries with relatively large proportions of Doubtful or Dismissive respondents include Nigeria (15%), Benin (12%), Kenya (11%), Congo (12%), and Tanzania (10%).

The selection of the top 15 emitters was based on World Bank data on total greenhouse gas emissions in 2019, which is the most recent year for which data is available. Our report excludes China, Russia, and Iran, as no survey data were collected from these countries.

The data in this report are based on a survey of 108,946 Facebook monthly active users, aged 18 and older. The survey was conducted from March 25 – April 14, 2022. Sampled Facebook users received an invitation to answer a short survey at the top of their Facebook News Feed and had the option to click the invitation to complete the survey on the Facebook platform.

Audience segmentation is based on the Six Americas Super Short Survey (SASSY), a  four-question online questionnaire that allows respondents to identify which segment they belong to ( Chryst et al., 2018 ). Only respondents who answered all four questions were assigned a segment: if they skipped any of the four questions, they were assigned to the “no segment” group.

It should be noted that we have previously reported tailored audience segmentations for a number of countries which identified different numbers of segments (e.g., Global Warming’s Four Indias and Climate Change’s Four Irelands ). However, these studies were based on in-depth, nationally representative surveys using different interviewing and segmentation methodologies.

Verner, M., Marlon, J., Carman, J., Rosenthal, S., Ballew, M., Leiserowitz, A., Buttermore, N., & Mulcahy, K. (2023). Global Warming’s Six Audiences: A cross-national comparison in nearly 200 countries and territories worldwide. Yale University. New Haven, CT: Yale Program on Climate Change Communication.

Funding Sources

The Yale research team was supported by the MacArthur Foundation and the Schmidt Family Foundation.

International Attitudes & Behavior

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Global Environmental Change: Understanding the Human Dimensions (1992)

Chapter: 4 human consequences and responses, 4 human consequences and responses.

Since before recorded history, environmental changes have affected things people value. In consequence, people have migrated or changed their ways of living as polar ice advanced and retreated, endured crop failures or altered their crops when temperature and rainfall patterns changed, and made numerous other adjustments in individual and collective behavior. Until very recently, people have responded to global phenomena as if they were local, have not organized their responses as government policies, and have not been able to respond by deliberately altering the course of the global changes themselves. Things are different now from what they have been for millennia.

This chapter examines the range of human consequences of, and responses to, global environmental change. We begin by developing the concept of human consequences and showing why, to understand them, it is critical to understand the variety of human responses to global change. We then offer a framework for thinking about human responses and discuss the pivotal role of conflict. The next section examines three cases that illustrate many of the major factors influencing the human consequences of global change. The following sections describe the human systems that are affected by or respond to global change, and how they interrelate. We conclude by offering some general principles for research and some research implications.

UNDERSTANDING HUMAN CONSEQUENCES

Many human actions affect what people value. One way in which the actions that cause global change are different from most of these is that the effects take decades to centuries to be realized. This fact causes many concerned people to consider taking action now to protect the values of those who might be affected by global environmental change in years to come. But because of uncertainty about how global environmental systems work, and because the people affected will probably live in circumstances very much different from those of today and may have different values, it is hard to know how present-day actions will affect them. To project or forecast the human consequences of global change at some point in the relatively distant future, one would need to know at least the following:

the future state of the natural environment,

the future of social and economic organization,

the values held by the members of future social groups,

the proximate effects of global change on those values, and

the responses that humans will have made in anticipation of global change or in response to ongoing global change.

These elements form a dynamic, interactive system (Kates, 1971, 1985b; Riebsame et al., 1986). Over decades or centuries, human societies adapt to their environments as well as influence them; human values tend to promote behavior consistent with adaptation; and values and social organization affect the way humans respond to global change, which may be by changing social organizations, values, or the environment itself.

This complex causal structure makes projecting the human consequences of global change a trickier task than is sometimes imagined. It is misleading to picture human impacts as if global change were like a meteorite striking an inert planet, because social systems are always changing and are capable of anticipation. So, for example, an estimate of the number of homes that would be inundated by a one-meter rise in sea level and the associated loss of life and property may be useful for alerting decision makers to potentially important issues, but it should not be taken as a prediction, because humans always react. Before the sea level rises, people may migrate, build dikes, or buy insurance, and the society and economy may have changed so that people's immediate responses—and therefore the costs of

global change—may be different from what they would be in the present.

One may imagine human consequences as the output of a matrix of scenarios. Assume that four sets of scenarios are developed for the futures of the natural environment, social and economic organization, values, and policies. Joining together all combinations of one scenario from each set, and adding assumptions about people's immediate responses, would generate an extensive set of grand scenarios. The human consequences of global change could then be defined as the difference between the state of humanity at the end of one grand scenario and the state of humanity at the end of a base case or reference scenario with a different natural-environment component. By this definition, a particular change in the natural environment has different consequences depending on the scenarios assumed for society, values, and responses.

Building these scenarios, identifying the most probable ones, and assessing their outcomes would be an overwhelming analytic task. Rather than trying to set a research agenda for that task, we undertake in this chapter a less demanding but still very difficult task: to focus on human responses to global change broadly conceived. We do not discuss ways to improve forecasts of the state of the natural environment; that topic is outside the range of human dimensions. Neither do we devote much attention to improving forecasts of social and economic organization or of human values, even though these topics clearly belong to the social sciences and are critical to understanding the effects of global change. We bypass these issues because the need for improved social, economic, and political forecasting is generic in the social sciences, and addressing this broad need would take us far beyond our charge to focus on human-environment interactions. We offer only limited discussion of how future global change might proximally affect what humans value, because the variety of possible global changes and the uncertainty about the effects of each make it far too difficult to go into detail. Instead, we review basic knowledge about how human systems respond to external stresses, in the context of discussing human responses.

In our judgment, understanding human responses is key to understanding the human consequences of global change. We do not mean to downplay the importance of certain kinds of research that do not focus explicitly on responses. Two such research traditions, in particular, are highly relevant. The impact-assessment tradition involves projecting the human consequences of a

range of natural-environment scenarios under given assumptions about human response. The tradition of post hoc case analysis involves assessing the actual human outcomes after past environmental changes (and given the responses that actually occurred), in the hope of drawing more general conclusions. Research in these traditions, combined with analysis of human response, can offer valuable insights into the human consequences of global change. We discuss that research as appropriate in this chapter and in Chapter 5 .

S OME D IMENSIONS OF H UMAN R ESPONSE

The human responses relevant to global change differ along several dimensions. We consider the following analytic distinctions useful for thinking about the range of responses available.

Responses to Experienced Versus Anticipated Change

People and social institutions may respond to environmental change as it is experienced (post facto) or as it is anticipated. 1 In the past, people responded mainly to experienced environmental change; only in very recent history, because of increasing scientific knowledge, has there been any rational basis for anticipatory responses. Policy makers and others are now faced with a variety of options, some of which involve anticipatory action and some of which depend on awaiting the experience of global change.

Deliberate Responses Versus Actions with Incidental Effects

Some human actions can be taken deliberately in response to global change. For instance, people can build dikes to keep out rising seas or reduce greenhouse gas emissions to mitigate global warming. Human actions can also affect human responses to global change incidentally to their intended purposes. For example, European settlement of the Americas gave Europeans and, later, others access to a wider variety of food crops, making human survival less dependent, at least in principle, on a small number of staples that might be vulnerable to altered growing conditions caused by environmental change. World markets have subsequently reduced the number of major staple foods so that, in practice, people may eat no larger a variety of foods than before (Plotkin, 1988). High taxes on gasoline in Europe and Japan, enacted for reasons unrelated to the global environment, encouraged

development and purchase of small, fuel-efficient automobiles that incidentally slow the pace of global warming. By bringing about technological change, these taxes also incidentally have helped make it easier for all countries—even those without high gasoline taxes or companies that produce fuel-efficient automobiles—to respond to the challenge of global warming with improved energy efficiency.

Changes in society that incidentally affect human responses to global change are important both directly and because they could become tomorrow's deliberate responses. For example, gasoline taxes, which were not initiated with the global environment as a consideration, could be increased to cut CO 2 emissions. Studies of the incidental effects of such actions might inform decision makers about what could happen without deliberate intervention and about which present policies might make societies more robust in the face of global change. Both kinds of knowledge are essential for informed policy debates.

Coordinated Versus Uncoordinated Responses

Response to global change may be coordinated, as through the policies of governments or trade associations aimed at eliciting the same action from many actors, or uncoordinated, as with independent actions of households or small firms. Both types of response can be either anticipatory or post facto; both can affect global change either deliberately or incidentally. Moreover, coordinated and uncoordinated responses can be connected to each other, in that coordinated actions by governments and industries can create new options for uncoordinated actors, prohibit responses, or raise or lower their costs.

Interventions at Different Points in the Process

Figure 4-1 elaborates on Figure 2-2 to show how human action can intervene at any point in the cycle of interaction between human and environmental systems to protect against threats to what humans value. We offer the following rough distinctions among types of interventions. 2

The term mitigation is generally used to describe interventions on the human causes side of the diagram. Mitigation includes all actions that prevent, limit, delay, or slow the rate of undesired impacts by acting directly or indirectly on environmental systems. Mitigation can operate at various points in the causal cycle.

Interactions between human and environmental systems and the role of various types of human response. Lightly shaded boxes repeat the relationships presented in Figure 2-2 .

It may involve direct interventions in the environment (type E in the figure) to counteract the effects of other human actions, direct interventions in the proximate human causes (type P), and interventions in the human systems (type H) that drive global change, intended to have an indirect or downstream effect on the proximate causes.

For example, global warming is the direct result of a change in the earth's radiative balance; humans can mitigate global warming by any actions that slow the rate of change or limit the ultimate amount of change in the radiative balance. 3 They can intervene in the environment (type E), for example by directly blocking incident solar radiation with orbiting particles or enhancing the ocean sink for carbon dioxide by adding nutrients. They can intervene in the proximate causes (type P), by regulating automo

bile use or engine design to cut carbon dioxide emissions or limiting the use of certain nitrogen fertilizers to reduce nitrous oxide emissions. They can intervene in human systems (type H) and indirectly control the proximate causes, by investing in research on renewable energy technologies to replace fossil fuel or providing tax incentives for more compact settlements to lower demand for transportation.

Mitigation of ozone depletion might, in principle, involve release of substances that interact chemically with CFCs, producing compounds with benign effects on the stratospheric ozone layer (type E), limiting emissions of chlorofluorocarbons (CFCs) and other gases that deplete ozone (type P), or developing alternative methods of cooling buildings that do not rely on CFCs (type H). Mitigation of threats to biological diversity might include, at least in principle, engineering new varieties, species, or even ecosystems to save diversity, if not individuals (type E); limiting widespread destruction of tropical forests, estuaries, and other major ecosystems (type P); or promoting systems of land tenure and agricultural production that decrease the pressure for extensive development of tropical forests (type H).

Humans can intervene in several ways on the response side of the cycle. Such actions are sometimes generically called adaptation , but there are important distinctions among them. One type of response, which can be called blocking , prevents undesired proximate effects of environmental systems on what humans value. It can be described by example. If global climate change produces sufficient warming and drying (drought) on a regional scale, it may threaten the region's crops; development and adoption of drought-resistant crops or crop strains can break the connection between environmental change (drought) and famine by preventing crop failure. Similarly, loss of stratospheric ozone threatens light-skinned humans with skin cancer, through exposure to ultraviolet radiation; avoidance of extreme exposure to sun and application of sunscreens help prevent cancer, although they do not mitigate the destruction of the ozone layer. Tropical deforestation threatens species with extinction by eliminating their habitats; creation of forest preserves would provide many species sufficient habitat to survive, while doing little to slow net deforestation.

Another type of adaptive response is to prevent or compensate for losses of welfare that would otherwise result from global change. Such actions can be called adjustments . 4 They neither mitigate environmental change nor keep it from affecting what people value, but rather intervene when a loss of welfare is imminent or after

it has begun to be manifest. Examples include evacuation from areas stricken with flood or drought, food shipments or financial assistance to those remaining in such areas, and development of synthetic substitutes for products previously obtained from extinct species. 5

Yet another type of response, sometimes called anticipatory adaptation, aims to improve the robustness of social systems, so that an unchecked environmental change would produce less reduction of values than would otherwise be the case. 6 This type of intervention does not alter the rate of environmental change, but it lowers the cost of any adjustments that might become necessary. It can be distinguished, at least in theory, from type H mitigation in that it does not necessarily alter the driving forces of global change. An example is diversification in agricultural systems. Farmers, regions, and countries that rely on a range of crops with different requirements for growth may or may not produce less greenhouse or ozone-depleting gases than monoculturists. But polycultures are more robust in the face of drought, acid deposition, and ozone depletion. There may be crop failure, but only in some crops. Similarly, families and communities that have both agricultural and nonagricultural income are harmed less by the same threats than purely agricultural groups. They have other sources of income and can purchase crops from elsewhere. 7

All social systems are vulnerable to environmental change, and modern industrial societies have different vulnerabilities from earlier social forms. Modem societies have built intricate and highly integrated support systems that produce unprecedented material benefits by relying critically on highly specialized outputs of technology, such as petrochemical fertilizers and biocides; hybrid seeds; drugs and vaccines; and the transmission of electricity, oil, and natural gas from distant sources. Although these complex sociotechnical systems contain great flexibility through the operation of global markets, they may have vulnerabilities that reveal themselves in the face of the changes that these systems have helped create. For instance, modern societies have become highly dependent on fossil fuels and vulnerable to a serious disruption of supply or distribution systems. They also support much larger and denser populations than ever before; such populations may be vulnerable to ecological changes affecting the viability of their food supplies.

Evidence from studies of disasters suggests that the poor, who lack diversified sources of income, political influence, and access to centralized relief efforts, tend to be worst off (Erikson, 1978;

Kroll-Smith et al., 1991; Mileti and Nigg, 1991). However, studies to assess the vulnerabilities of larger human systems, such as national or world food or energy systems, are rarely done (e.g., Rabb, 1983). The far side of vulnerability is also little studied: When a system fails to resist environmental pressure, under what conditions does it return to its previous state? If it undergoes permanent change, what determines the nature of the new state?

T HE P IVOTAL R OLE OF C ONFLICT

An important consequence of global environmental change is conflict, because global change affects what humans value, and different people value different things. When U.S. energy use threatens the global climate or land clearing in Brazil threatens the extinction of large numbers of species, people around the world are understandably concerned. They may express a desire—or even claim a right—to influence the choices of people or governments continents away. And the people or countries subjected to those claims may resist, especially when they feel that changing their behavior will mean suffering. The further global change proceeds, the more likely it seems that it will be a source of conflict, including international conflict, over who has a right to influence the activities implicated as causes, who will pay the costs of responding, and how disputes will be settled.

A Current Controversy: To Mitigate or Not to Mitigate?

One of the most heated policy debates about responses to a global change is between advocates of immediate efforts to mitigate global warming and those who would postpone such action. This debate arose within the committee, even though we were not charged with recommending strategies for response to global change. We offer the following brief, sharply stated version of the debate to highlight some important characteristics of controversies about global change: that they are partly, but not entirely, fact-based; that they are likely to persist even in the face of greatly increased knowledge about the causes of global change; and that they are pervasive, even in discussions restricted to research priorities.

In one view, the wise course of action on global warming is to conduct research on the phenomenon but not to take action to slow or mitigate it until the phenomenon is better understood. Proponents of this view make the following arguments:

Uncertainty of global change . The nature and extent of global warming in the future is highly uncertain because of incomplete knowledge of the relevant properties of the atmosphere, oceans, biosphere, and other relevant systems. It is wasteful for society to expend resources to prevent changes that will not occur anyway. Moreover, the mitigation efforts may themselves set in motion undesired changes.

Adjustment will make mitigation unnecessary . Human systems can adjust to global climate changes much faster than they are likely to occur. The projected doubling of atmospheric carbon dioxide levels will take place about 80 years from now. By contrast, financial markets adjust in minutes, administered-market prices in weeks, labor markets in years, and the economic long run is usually reckoned at no more than two decades. The implication for action is that what individuals and organizations do on their own in anticipating climate change may be sufficiently successful that organized, governmental responses will be superfluous. The impact of climate change will reach people through slow price increases for the factors of production; in reasonably well-functioning markets, economic actors adapt readily to such changes. They invent industrial processes that economize on scarce inputs, find substitutes, purchase energy-efficient equipment when energy prices are rising, and so forth. In the past, such adjustments have contributed to human progress, and there is every reason to expect that pattern to continue.

Don't fight the wrong war . It makes no sense to act like the generals who built the Maginot Line for the wrong war or to construct dikes for cities whose populations will have moved or dams to water crops that will be grown elsewhere. Technological and social changes often eliminate problems without any specific mitigation efforts by changing the offending technology or making it obsolete. For example, boilers no longer explode on trains because they no longer use steam engines; horses are no longer the main polluters of urban streets. Concern about the greenhouse effects of fossil fuel burning will prove premature if development of fusion or solar energy technology can replace most fossil fuel use over the next 50 years.

Better policy options may lie on the horizon . Further research may identify more effective and less costly interventions than those now available. For example, it has recently been suggested that adding iron to the oceans to fertilize phytoplankton that would absorb carbon dioxide from the atmosphere may be a way to address the greenhouse effect (Martin et al., 1990). That

proposal, whatever its ultimate feasibility or desirability (Lloyd, 1991), demonstrates that improved understanding of biogeochemical systems might generate promising new proposals for mitigating global change. Improved understanding of social systems has reasonable potential to discover other classes of effective response.

It may be more costly to act now . Actions that can be postponed will be less burdensome because of continuing economic progress. If people living in the 1890s had invested in preventing today's environmental problems, their expense on our behalf would probably have been made on the wrong problems, and it would have been an inequitable transfer of resources from a poorer generation to a richer one. It probably makes no more sense for the current generation to sacrifice to benefit a future, even wealthier generation. This is the argument for a positive social discount rate. It assumes that expenditures made now could otherwise be invested at compound interest in improvements in human well-being. If the growth rate for such investment exceeds the average rate at which environmental problems develop, people will be better off in the future if they do not spend on mitigation now.

Proponents of immediate mitigative action make the following arguments:

Action now is more feasible and effective than action later . It is in the nature of exponential growth processes that the earlier the growth rate decreases, the greater the final effect. Bringing down the birth rate in India to two children per couple in 1995 rather than in 2005 can make a difference of 300 million people by the time the Indian population stabilizes (Meadows, 1985). To achieve the same effect by starting later would impose greater restrictions on the people living at that time. It is therefore easier to mitigate the effects of exponential growth the sooner the effort is made.

It is easier to adjust to slower change . Mitigation is prudent because of the long time lags in the global environmental system. By the time it becomes clear that a response is needed, it may be too late to prevent catastrophe if the change is proceeding rapidly. Even if catastrophe is unlikely, mitigation that slows the rate of change makes it more likely that adjustments can be made in time. This is clearly the case for nonhuman organisms, such as tree species that can adjust to climatic change by migrating, as seedlings move to more favorable locations. Such species have a

maximum rate of migration, so can adjust to climatic change below that rate. 8 The same principle probably also applies to human adjustments to major environmental change.

It is wise to insure against disaster . Mitigation in the face of possibly catastrophic outcomes is like taking out insurance against flood and fire. The insurance expenses are bearable, but the expenses of catastrophe may not be.

Avoid irretrievable error . It is wise to mitigate against potentially irretrievable losses. The clearest example is species extinction. If species are valued for themselves, their loss is irretrievable; even if they are valued only for what benefits they may have for humanity, species loss may be irretrievable. Other environmental values, such as loss of the life-supporting capacity of wetlands or large bodies of water, may also be irretrievable; often we do not know until the values are lost.

Avoid high-risk environmental experiments . Humans are now conducting large-scale uncontrolled experiments on the global environment by changing the face of the earth and the flows of critical materials at unprecedented rates. It is prudent to limit the pace and extent of such experiments because of the likelihood of unanticipated consequences. Like natural mutations, most of these experiments are probably destined to fail, and there is only one global environment to experiment on. As the extent of human intervention in the global environment continues to increase, so does the strength of this argument. The argument supports mitigation efforts that slow ongoing human interventions in the environment, but generally not those that would stop greenhouse warming by new interventions in the global environment.

Economic arguments do not encompass some environmental goods . The discount-rate argument is specious in the general case because the costs and benefits of postponing action are not always commensurable. Some important and meaningful tradeoffs can be made on economic grounds, for instance, between investing in renewable energy development and in directly limiting the burning of fossil fuels. But sometimes the economic logic makes no sense. If current economic activity destroys die life-support systems on which human life depends, what investment at compound interest could ever recoup this cost? Economic arguments also cannot deal with some things—including the balance of nature—on which people place intrinsic or spiritual value. To the extent people want to preserve such values, mitigation is the only acceptable approach. Moreover, economic accountings systematically undervalue things—such as genetic resources—for

which there are few property rights or for which economic value is only potential.

Some mitigative action is fully justified on other grounds . A good example is investments in energy efficiency that provide an excellent return on investment even with narrow economic calculations. Such actions can achieve the benefits of mitigation at no extra cost, while providing other benefits.

Implications of Conflict About Human Response

Many controversies are beginning to develop out of concerns with global change. One pits Third World countries against the developed countries that are now becoming concerned with limiting use of fossil fuels and restricting the felling of tropical forests. The Third World position, of course, is that other countries used fossil fuels and undeveloped frontiers for their economic development, and fairness dictates that the poorer nations now have their turn. Many analysts believe that if large-scale climate change results from human activities, the poorer countries are likely to suffer most because they lack resources they could use to adapt. Such an outcome would produce yet other conflicts.

The controversies about global change are only partly fact-based. True, some of the disagreements might fade with better knowledge about the global environment and the likely effects of different feasible responses. As it became clear that expected global warming over the next 50 years could not cause the breakup of the West Antarctic icecap, the flood-prevention rationale for slowing greenhouse gas emissions became considerably weaker. A response such as dike building seems much more appropriate when the sea threatens only a few areas. And if it became clear what each policy option—at the local, national, and international levels—would accomplish if enacted, some of them could easily be rejected.

But knowledge often fails to resolve controversy. It frequently raises new disputes or calls old beliefs into question. And even when new knowledge reduces uncertainty, controversies persist because not only facts, but also important interests and values, are at stake. Informed people disagree because the remaining uncertainty leaves room for judgment, because they may assume different scenarios about the future of society, and because an outcome that harms what one person values may enhance what another values. Those impressed with the potential benefits of economic growth tend to line up against those who fear of the

potential costs; those with a strong faith in the ability of human ingenuity to solve life's problems line up against those awed by what is at stake; those who stand to benefit from an outcome line up against those who stand to lose. When faced with choices, some prefer international solutions to global problems, others see national action as more feasible; some favor market adaptations, others, community-based action outside the market and the state; some are attracted to large-scale technological solutions, others see them as cures that may be worse than the disease. In short, the debates are not only about the workings of human and environmental systems, but also about political and economic interests, conflicting values and faiths, differing assumptions about the future, and different judgments about resiliency in the face of the unexpected.

Research on Conflict Studies of environmental and technological conflict are a significant part of social research on conflict (e.g., Nelkin, 1979; Mazur, 1981; Freudenburg and Rosa, 1984; Jasper, 1988; Clarke, 1989). Issues of global environmental change have all the features characteristic of the most difficult technological controversies: awareness of human influence on the hazards, serious worst-case possibilities, the possibility of widespread and unintended side effects, delayed effects not easily attributable to specific causes, and lack of individual control over exposure (National Research Council, 1989b:57-62).

Social science can help illuminate the nature of environmental controversies and evaluate ways of managing them. Social scientists interested in environmental policy have studied the conditions shaping and favoring the resolution of environmental controversies and the role of scientific, governmental, and mass media communication in the decision process (e.g., Dietz and Rycroft, 1987; Gould et al., 1988; Jasanoff, 1990; Nelkin, 1979, 1988; National Research Council, 1989b). Some have begun to consider the various ways environmental change might lead to conflicts with the potential for violence (e.g., Homer-Dixon, 1990).

Social scientists specializing in conflict have developed generalizations that might be more thoroughly applied to environmental conflict. For example, conflicts may be based mainly on ideology, interest, or understanding (Aubert, 1963; Glenn et al., 1970; Rapoport, 1960, 1964; Hammond, 1965; von Winterfeldt and Edwards, 1984; Syme and Eaton, 1989), and different types of conflict tend to yield to different tactics of resolution (e.g., Druckman and Zechmeister, 1973; Druckman et al., 1977). Defining an environ-

mental conflict as either one of understanding or one of interests and values affects which groups and arguments are considered legitimate in policy debates (Dietz et al., 1989). The nature of the relationship between the parties to a conflict can determine whether the conflict focuses on ideological positions (e.g., Campbell, 1976; Zartman and Berman, 1982), differences in understanding (e.g., Axline, 1978), or differences in interests (e.g., Strauss, 1978). And the behavior of the parties to a conflict depends on the pattern and relative strength of incentives to compete and to cooperate (e.g., Pruitt and Kimmel, 1977), the probability of continued interaction in the future (e.g., Axelrod, 1984), and on whether two or more parties are involved (Groennings et al., 1970; Hopmann, 1978; Putnam, 1988).

More research seems warranted to use existing knowledge about conflict to illuminate the ways social conflict may result from global environmental change. This research would investigate the ways environmental changes may affect organized social groups and their resource bases and would hypothesize links between those effects and conflict. A first step is to construct an analytical framework for identifying the possible routes from particular environmental changes to particular types of conflict. The framework of Homer-Dixon (1990) provides a start, for causes of violent conflict. Case analyses of past social conflicts can be used to assess hypotheses drawn from such analytic frameworks.

Research on Conflict Resolution and Management Social scientists have also identified a number of approaches for resolving or managing policy disputes, some of which are beginning to be studied in the context of environmental conflicts. These include mediation techniques intended to address the value dimension of environmental conflict (e.g., Ozawa and Susskind, 1985); facilitation procedures that emphasize problem-solving discussions and have proved useful as a prelude to negotiation (Burton, 1986; Druckman et al., 1988); techniques of separating values from interests to makes conflicts appear smaller and easier to solve (Fisher, 1964; but see Druckman, 1990); efforts to focus on shared principles for decisions (Zartman and Berman, 1982) or to discuss values as ranked priorities rather than ideological differences (Seligman, 1989); policy exercises that emphasize creative use of scientific knowledge to solve environmental problems (Brewer, 1986; Toth, 1988a, b); and computer software for dealing with the cognitive and political aspects of both conflicts over the interpretation of data for environmental management (Hammond et al., 1975; Holling, 1978).

The nature of technological conflicts suggests, however, that over the long-term, management is a more realistic goal than stable resolution. Recent work on risk communication is potentially relevant to social responses to global change because global change problems, like those to which that literature refers, are characterized by high levels of scientific uncertainty and great potential for conflict about social choices (Covello et al., 1987; Davies et al., 1987; Fischhoff, 1989; National Research Council, 1989b; Stern, 1991). This work suggests that institutions responsible for decisions about global change will also have to manage conflict. These institutions will need to provide accurate information, but should not expect information to resolve conflict. The institutions will need to make a place for the stakeholders to be represented from the earliest stages of the decision process, ensure openness in processes of policy decision, include mechanisms for the main actors to have access to relevant information from sources they trust, and use the conflicting perspectives and interpretations of current knowledge and uncertainty to inform the ongoing debate (National Research Council, 1989b; Stern, 1991).

Research Needs Relatively little is known about the structure of particular conflicts about global change at the local, national, and international levels or about which means will be most effective in dealing with them. Therefore, we recommend increased empirical research, including both field studies and laboratory-simulation studies, to clarify the sources and structures of particular environmental conflicts and to test the efficacy of alternative techniques for their resolution and institutions for their management.

HUMAN RESPONSE: THREE CASES

In Chapter 3 we presented cases to illustrate how human actions can contribute to the causes of global change. Here we present three cases to illustrate the human consequences of, and responses to, environmental change. Taken together, they show the importance of all the major human systems involved (described later in the chapter) and the ways that conflicts are played out and choices made within these systems.

I NTERNATIONAL R EGULATION OF O ZONE -D EPLETING G ASES

As mentioned earlier, the most successful effort to date to address a global environmental problem by international agreement

is the ozone regime, articulated in the 1985 Vienna Convention for the Protection of the Ozone Layer, the 1987 Montreal Protocol on Substances That Deplete the Ozone Layer, and the 1990 London Amendments to the protocol. This regime, in its current form, commits its members to phasing out the production and consumption of CFCs and a number of related chemicals by the year 2000. The regime represents the first concerted international effort to mitigate ''a global atmosphere problem before serious environmental impacts have been conclusively detected'' (Morrisette, 1989:794).

The political history of the ozone regime begins as a national issue in the United States and a handful of other Western countries in the early 1970s, in connection with emissions from supersonic transport (SST) aircraft and then from aerosol spray cans (Downing and Kates, 1982; Morrisette, 1989). Environmental groups organized opposition to the development of the SST and to the extensive use of aerosols. Individual responses led to a sharp drop in sales of aerosol products (Morrisette et al., 1990). The U.S. Congress, prodded by government studies supporting the CFC-ozone depletion theory and its links to skin cancer, approved the Toxic Substances Control Act of 1976, which among its other provisions, gave the Environmental Protection Agency (EPA) the authority to regulate CFCs. In 1978, the United States became the first country to ban the nonessential use of CFCs in aerosols. However, the EPA ruled that other uses of CFCs, such as in refrigeration, were both essential and lacked available substitutes.

Ozone depletion emerged as a major international issue in the 1980s. This occurred primarily as a result of initiatives by the United Nations Environment Programme (Morrisette, 1989) and the actions of the international scientific community (Haas, 1989), with the support of the international environmental movement. The Vienna convention of 1985 embodied an international consensus that ozone depletion was a serious environmental problem. However, there was no consensus on the specific steps that each nation should take.

A number of events in 1986 and 1987 created a new sense of urgency about the depletion of stratospheric ozone. These included a rapid growth in demand for CFCs due to new industrial applications and the end of a global economic recession; important new studies by the World Meteorological Organization, the National Aeronautics and Space Administration, the Environmental Protection Agency (EPA), and the United Nations Environment Programme; and, most important, the widely publicized

discovery by scientists of the Antarctic ozone hole in 1985. In January 1986, EPA initiated a series of workshops designed to build an international scientific consensus supporting the need to control the use of CFCs. In the same year, DuPont announced that its scientists had determined that CFCs were the most likely cause of ozone depletion. These events persuaded American officials of the need for decisive international action. When negotiations on a protocol to the Vienna convention for controlling CFCs resumed in December 1986, the United States adopted a firm position, calling for an international treaty not only freezing production of CFCs but also reducing production and consumption.

Following extensive and complex negotiations, the Europeans, whose earlier opposition to a cutback in production had prevented agreement in Vienna, moved closer to the U.S. position. They were persuaded to do so by three factors: the weight of scientific evidence, pressures from their own domestic environmental groups, and the fear that, in the absence of a treaty, the United States might take unilateral action to impose trade sanctions. While compromises on several controversial points proved sufficient to gain Japanese and Soviet adherence, the major developing countries (e.g., China and India) did not become signatories to the Montreal Protocol.

Only after the Montreal Protocol was signed did the full extent of ozone depletion became public: ozone depletion over Antarctica reached a historic high in 1987, and the link to the release of CFCs became a matter of scientific consensus. DuPont responded by announcing that it planned to discontinue CFC production by the end of the century and, in March 1989, 123 countries called for the absolute elimination of production by the same date. A resolution agreeing to totally phase out all production and consumption of CFCs by the year 2000 was adopted by 81 countries in May 1989 at the first governmental review of the Montreal Protocol.

Taking advantage of this momentum, the parties to the Montreal Protocol, meeting at a review conference in London in June 1990, were able to negotiate a series of strong amendments. These amendments accelerate the phaseout schedule for CFCs and halons and add methyl chloroform and carbon tetrachloride to the list of chemicals to be eliminated. Equally important, the amendments establish an international fund to be used to assist developing countries in switching to substitutes for CFCs in the production of refrigerators and air conditioners. On the strength of this

development, both China and India agreed to become members of the international ozone regime.

Why was it possible to reach a broad international agreement restricting CFCs? Analysts have identified four important factors: an evolving scientific consensus; a high degree of public anxiety in developed countries about the risks associated with the continued use of CFCs, due in large measure to an association with skin cancer; the exercise of political muscle by the United States; and the availability of commercial substitutes for CFCs (Haas, 1989; Morrisette, 1989). The last served the critical role of diminishing the opposition of the chemical industry to a phased reduction. When DuPont, the producer of 25 percent of all CFCs, decided to develop substitutes, it "forced other CFC manufacturers to follow suit or risk losing market share" (Haas, 1989:11). Haas adds that, because this issue could be resolved by a technical fix, it did not involve any hard choices and therefore may be unique in the annals of global environmental change.

Another important influence in getting CFCs on political agendas may have been the efforts of the scientific community, which has been influential in drawing attention to other environmental problems (Haas, 1991). Haas (1989) notes that it was initially a group of atmospheric physicists and chemists, most of whom worked in the United States, who attempted to place the issue of ozone depletion on the national and global environmental agendas, and that this community continued to press the issue throughout the 1980s. He argues that the speed of policy response in the United States may have been due to the "highly fragmented nature of American government and society [which] facilitates access of a strongly motivated group of technical experts" (p. 8). Thus, the access of a key group to policy debates at the national level may have influenced international action on CFCs.

The history of the ozone regime illustrates a number of key variables that affect the likelihood of reaching similar agreements on other global environmental problems (Sand, 1990b; Benedick, 1991). Further studies are desirable to clarify how these variables interact:

the emergence of scientific consensus on the causes of global environmental change;

the number of actors responsible for the proximate causes of the global change;

the nature and global distribution of the harm that might result from inaction;

the distribution of the burdens of regulation on the consumers, producers, and employees whose behaviors must change;

the importance of national regulations as a precursor to the emergence of international ones; and

the need for strong leadership in international forums.

It also suggests that international agreements can be affected by the structures of national political systems, informal international communities, and markets that would be critically affected by agreement.

T HE U.S. E NERGY C ONSERVATION A CHIEVEMENTS OF 1973-1985

Energy efficiency is probably the most widely accepted strategy for mitigating global warming. The energy shocks of the 1970s led to significant improvements in the energy productivity of Western industrialized economies. The U.S. experience is typical and instructive.

Between 1973 and 1985, the United States reduced its energy intensity—the ratio of energy use to economic output—by 25 percent. 9 Other industrialized capitalist countries made similar achievements, reducing energy intensity, usually from much lower initial levels, by an average of 21 percent during that period (International Energy Agency, 1987). The change was a sharp contrast to the record of the previous two decades and to most of the twentieth century. Between 1953 and 1973, U.S. energy intensity was almost steady, decreasing at an average of 0.1 percent per year; at only two earlier periods in the century, 1918-1926 and 1948-1953, did energy intensity decrease at a rate above 2 percent per year (Schurr, 1984). To the extent that energy intensity can continue to improve in the United States and other countries, energy efficiency can make an enormous contribution to mitigating global warming. This section takes a closer look at how and why the change occurred in the United States and the implications for other countries.

Preexisting Trends

After increasing for 40 years, U.S. energy intensity declined fairly steadily between 1920 and 1953, before stabilizing for 20 years (see Table 4-1 ). Although the reasons are not well understood, the secular decline in energy intensity since 1920 has been attributed to improved efficiency in energy conversion, a

TABLE 4-1 Average Annual Percentage Rates of Change in Total Output and Energy Intensity in the United States Private Domestic Business Economy, 1899-1981

shift in the economy away from heavy manufacturing, and technological improvements throughout the economy associated with a shift to more flexible energy sources: oil, gas, and electricity (Schurr, 1984). The decrease in energy intensity with the 1973 oil shock, and again with the 1979 shock, marked a sharp break from the previous 20 years; from 1973-1981, intensity decreased at a rate about 2 1/2 times the average of the previous 53 years.

Uncoordinated Responses to Recent Events

The behavioral change after 1973 was largely due to the oil shocks of 1973 and 1979, which rapidly altered energy prices, changed perceptions of the future price and availability of fossil fuels, and brought about policy changes. Energy users made three effective kinds of responses (U.S. Department of Energy, 1989; Schipper et al., 1990). First, they changed the way they operated energy-using equipment, curtailing heat and travel, and improving management, such as by tighter maintenance of furnaces. Such changes accounted for 10-20 percent of national energy savings achieved in 1986 (compared with the pre-1973 trend; estimates from U.S. Department of Energy, 1989) but are easily reversed when energy prices drop or incomes rise, as they did in the 1980s.

Second, energy users adopted more energy-efficient technology to provide the same service with less energy use, either by retrofitting existing equipment (e.g., insulating buildings, installing reflecting windows) or by replacing existing equipment with more energy-efficient models. These improvements were responsible for 50-60 percent of total energy savings by 1986.

Third, the mix of products and services in the economy changed. Demand fell sharply in energy-intensive industries, such as primary metals, relative to less energy-intensive industries; small cars got an increased share of the automobile market; and commercial airlines improved the match between aircraft size and demand on passenger routes. Together, such shifts accounted for about 20-30 percent of the energy savings achieved in 1986.

Higher real energy prices are generally considered the most important single explanation for these responses (International Energy Agency, 1987; U.S. Department of Energy, 1989). However, price is not the whole story. Although the two energy shocks of the period had very similar price trajectories, the effects on the economic productivity of energy differed markedly after the first two years (see Figure 4-2 ). For the first two years of each shock, real energy prices increased about 40 percent and energy productivity increased about 5 percent. But over the longer-term, the second shock had much more effect than the first. A five-year price increase of about 45 percent in 1973-1978 increased energy productivity 7 percent; a similar increase in 1978-1983 increased energy productivity 18 percent. Moreover, the trend continued through several years of falling real energy prices.

Why the different reactions to the two energy shocks? One explanation is perceptions: it took the second shock to get energy

FIGURE 4-2 Changes in indexed real energy prices and energy intensity in the U.S. economy after the energy shocks of 1973 (A) and 1979 (B).

users' attention—to convince them that higher energy prices were here to stay. Another is that the decision environment had changed by 1979 in ways that made it more likely the system would respond to price signals. Government policies to promote energy-efficient technology and provide necessary information were in place by 1979, making it easier for energy users to respond effec-

tively to price; the learning curve for policy implementation had had time to progress; and entrepreneurs were ready to offer energy-efficient technologies and management programs that had not been developed in 1973. Moreover, U.S. energy inefficiency had helped open the door to foreign competition in the automobile, steel, and other industries, with the result that U.S. firms began taking efficiency of all kinds more seriously. Because these explanations reinforce each other, it is difficult to estimate their relative magnitude.

The multiple explanations suggest that the price effect depends on other factors: technological change, policy choices, change in industrial structure, and information processing by energy users. Since these factors can be changed independently of energy prices, it seems likely that with appropriate policies in place, energy intensity might have improved faster than it did, even in the apparently price-responsive 1979-1985 period.

Policy Responses and Implementation

Energy conservation policy in the United States has been predicated on the theory that government should intervene chiefly to correct so-called market imperfections such as the tendency of a supply system based on market prices to produce too little environmental quality (because individual consumers cannot be charged for it) and too little information on energy-efficient technologies and their costs. The government can also intervene to mitigate regulatory and institutional barriers to the functioning of the price system. Following this theory, many U.S. efforts to promote energy efficiency have relied on positive financial incentives (e.g., tax credits, utility rebate programs) and on information. Experience with these efforts shows that the market imperfection theory needs to be expanded to take into account deviations in energy users' behavior from conventional economic rationality. 10 Often, rather than making decisions based on minimization of long-run costs, as theory postulates, energy users act on the basis of nonfinancial values (such as environmental preservation, interest in new technology, or enhancement of social status) or are influenced by information from informal social networks rather than more accurate expert information (see Stern and Aronson, 1984, for a review of evidence). Such processes within individuals and small groups have impeded the effectiveness of conservation programs in the United States, but when they are taken into account, programs became much more effective.

Evaluations of incentive and information programs show that, although they are sometimes very effective at increasing the pace of adoption of available technology, success varies greatly, even between nominally identical programs (Berry, 1990). For instance, home energy rating systems reach between 2 and 100 percent of homes, depending on the market (Vine and Harris, 1988), and utility companies offering exactly the same financial incentive program for home retrofits typically have participation rates that vary by a factor of 10 or more (Stern et al., 1986a).

Success depends on a number of features of implementation. A key is getting the attention of potential participants with appropriate marketing efforts, targeting of audiences, selection of trustworthy sources of information, and other basic principles of communication (Berry, 1990; Ester and Winett, 1982; Stern et al., 1986a; Vine and Harris, 1988; Dennis et al., 1990). Getting people's attention appears to be the main barrier to the success of financial incentive programs for home retrofits, so that, paradoxically, "the stronger the financial incentive, the more the program's success depends on nonfinancial factors" (Stern, 1986:211). Apparently, larger incentives ensure success among those who enter a program but do little to attract participants. Finding the proper intermediary, such as a builder, manufacturer, designer, or lender, can also be critical. Home energy rating systems have been introduced most effectively with the active support of the building and lending industries (Vine and Harris, 1988), and residential conservation programs, especially in low-income areas, have often depended for success on involving highly trusted local organizations, such as churches and housing groups (Stern et al., 1986a). Involving consumers in program design can help fit a program to its audience and locale (Stern and Aronson, 1984).

Thus, conservation policies and programs played a part in the U.S. response to the energy shocks of the 1970s, but they could have had a greater effect with better implementation. Improved policies and implementation, along with higher prices, are among the reasons energy productivity improved faster at the end of the 1973-1985 period than at the beginning. These three factors act in conjunction, however. If, for example, energy prices fall or remain stable, lowering energy users' motivation to change, some policy instruments will become less effective than they were in 1973-1985. The trends of the late 1980s demonstrate this effect (U.S. Department of Energy, 1989).

Implications for Future Climate Change

The technological potential for improvements in energy productivity are huge (National Academy of Sciences, 1991b; National Research Council, 1990a). However, the worldwide prospects for implementing technological changes, and therefore for mitigating the release of greenhouse gases, depends on the behavior of several human systems, including world markets for fossil fuels, national policies for economic and technological development and energy management, global social trends in government and the development of technology, and the behavior of individuals and communities.

The world energy price and supply picture will affect the spread of the Western improvements in energy productivity to other countries. Under conditions like those of the late 1980s, with relatively low energy prices and stable supplies, sharp further improvements in installed energy efficiency are unlikely, even in the Western industrialized countries, without new policy initiatives. The price motive for efficiency is weak, policies that rely on that motive are undermined, and the lowered cost of energy is a spur to economic growth, particularly in energy-intensive sectors. Given continuing population and economic growth, those conditions point to increases in energy use in the wealthy countries, although probably not at pre-1973 rates of increase. A new round of sharp price increases would cut energy use both by reducing economic activity and energy intensity, at least for a period.

The world picture also depends greatly on the development paths of growing economies. Industrialization is energy intensive, enough to have overcome the effects of the 1973-1985 oil shocks in relatively wealthy countries, such as Greece and Portugal, that were still industrializing. Consumers' choices are also important. Where increased income goes into homes and durable possessions, as in Japan, energy productivity is more likely to be higher than where it goes into personal transportation, as in the United States, or into refrigerators or other energy-using appliances, as may become the case in China.

The future of the dissolving socialist bloc countries holds many uncertainties. Many of these countries have highly energy-intense economies and therefore seem to have room for improved energy efficiency given the rise of markets and more democratic control of policy. However, they lack finances to develop technology or implement incentive or information programs and need time to design and implement effective policies for local conditions. Whether

development moves in industrial or postindustrial directions is also uncertain. Much room exists for research and for pilot experiments with policy options as ways to reduce the uncertainty.

These and other human systems will determine the extent to which the Western experience with energy efficiency will proceed further or be repeated in other countries. The future will depend on the ways these systems interact in each country and on the ways national and local policies intervene in them.

T HE H UMAN C ONSEQUENCES OF R EGIONAL D ROUGHT IN THE S AHEL

Intensification of the greenhouse effect is likely to alter rainfall patterns on a regional scale. As a rule, regions that receive increased rainfall are likely to benefit; decreased rainfall is the more serious concern. The history of the human consequences of severe drought can be instructive about the variety of human consequences of, and responses to, unmitigated climatic change.

The human role in causing drought in the Sahel region of sub-Saharan Africa is a matter of controversy. Throughout the modern history of drought-famine association in the region, there has been a tendency to interpret extreme events as indicators of trends and to attribute the presumed trends to human mismanagement of the local environment. In fact, Sahelian droughts have been recurrent events. The droughts of the 1970s and 1980s were preceded by several others in this century, one of which, in 1910-1915, resulted in intense famine with high mortality. The controversy over the human role in causing Sahelian drought revived with the drought of 1968-1974. The prevailing view was that desertification was an anthropogenic process reflecting deforestation, overgrazing, overfarming, burning, and mismanaged irrigation resulting in salinization of soil and water.

Lack of good data is a major obstacle to understanding the causes of Sahelian drought. Although some evidence supports the orthodox view, some recent research using remote sensing, field measurements, and intensive investigations of small areas has called that view into question. Observable ecological changes are less significant than had been supposed and correlate better with rainfall records than with land management (Mortimore, 1989).

Different Droughts, Different Responses

The consequences of Sahelian droughts in this century have depended on the ability of indigenous systems of livelihood to

make adaptations. During the century, these indigenous systems have undergone continual change, first as a result of policies of colonial powers, and later in response to postwar development policies promoting ''modernization'' and further integration into the global economy. There are competing views of the effects of these century-long trends in political economy on the ability of local populations to withstand drought. In one view, the main results were increased dependency and vulnerability; in the other, vulnerability decreased because of improved availability of medical care, famine relief, and a national infrastructure that allowed for easier. migration and food shipments (Kates, 1981).

The three major droughts of the century, in 1910-1915, in 1968-1974, and in the 1980s, have had different effects on the lives and livelihoods of the local populations. The 1910-1915 drought, which was of comparable severity to the drought of the 1970s, appears to have produced greater increases in mortality; its effects on malnutrition and on the social fabric are harder to determine (Kates, 1981). The knowledge base is better for comparing the droughts of the 1970s and 1980s. 11 Local conditions changed between those two periods. Population continued to increase at up to 3 percent annually, forests continued to be cut for fuel and farming, and other forms of resource exploitation probably continued at about the previous rates. Grazing pressure fell, owing to animal mortality but, by the 1980s, cattle holdings had recovered to 60 percent of predrought levels in some areas, and small livestock probably recovered more. On balance, the human demands on the local environment were at least as severe as before the 1968-1974 drought.

The drought of the 1980s was as severe as the previous one. Annual rainfall in 1983-1984 was of the same order as in 1972-1973, and in some areas of the Western Sahel, less. Crop failures and pasture shortages were equally serious. Yet famine did not occur on the same scale, and animal mortality was lower. Possibly food aid was earlier and better in some countries, but in northern Nigeria, where food aid was not a major factor in either period, social distress was noticeably less marked in the 1980s, even in the worst affected areas.

What explains the relatively low human cost of the 1980s drought? It was not the response of the affected governments. Political officials were taken by surprise about equally by both droughts. The people most experienced in surviving failures of agricultural production and managing the environment were those living in the affected areas, but this group had little influence on policy. Of the several political interests concerned with the drought prob-

lems, both international and national, the least powerful seems to have been that of the people in the affected areas. Consequently, proposals for new technologies for coping with the drought failed to take indigenous technologies and management systems seriously, and measures to strengthen the poor—for instance by insurance, improved access to resources, alternative job opportunities, and price supports—were rarely considered or given high priority.

A key to drought response appears to have been the role of indigenous forms of land use and response to food shortage. It is possible to distinguish two strategies of land use for areas like the Sahel that face recurrent drought or a long-term threat of declining rainfall. One strategy—maladaptive in the long run—is characterized by deforestation and overcultivation and leads to land degradation, decreases in productivity, and, in the event of drought, short-term collapse. Another—adaptive in the long run—is based on flexible land use, economic diversification, integrated agroforestry-livestock management, and intensive use of wetlands. This pattern tends to generate sustainable, intensive systems and is resilient in the face of drought.

Indigenous strategies of response to acute food shortage apparently enabled the Sahelian populations to survive notwithstanding the tardiness, inadequate scale, and maladministration of most relief programs. These strategies, which relied on economic diversification, such as using labor in urban areas to supplement agricultural income, have evolved in an environment of climatic uncertainty and confer a degree of short-term resiliency. Their future evolution is hard to predict. Continued integration into the world economy may improve roads and other infrastructure, thus enabling diversification; it may also increase pressure for development of cash crops and thus hasten land degradation.

Relationship of Policy to Indigenous Response Systems

The ability of indigenous systems of land use and crisis management to cut the link between drought and famine depends on various factors that sustain the indigenous systems. These include diversity of economic opportunities, absence of war, and appropriate national and international policies on migration. Critical variables include the development of infrastructure and the set of national policies governing access to land, trees, and water. The social distribution of wealth, particularly secure rights of individual or community access to natural resources, determines the extent of human vulnerability to drought. Although some impor-

tant international actors are coming to perceive these relationships, the political balance is quite different at the national level, where the relevant policies are enacted and enforced. Ruling and military elites, professionals in the civil service, traders (especially in grain), capitalistic farmers, livestock owners, wood fuel exploiters, and small farmers and herders all have separate and distinct interests in the outcome, and most of these interests do not accord high priority to sustainable environmental management or drought preparedness.

Although not enough is known to forecast the consequences of future Sahelian droughts, two alternative scenarios can be imagined. In the doomsday scenario, increasing numbers of people generate cumulative environmental degradation (overcutting of woodland, overcultivation of soils, overgrazing of pastures, and overirrigating and possibly overuse of water), suffer increasing food scarcities as available grain per capita declines, and either starve in huge numbers or migrate in distress to other areas where they become permanently dependent on international relief. In the optimistic scenario, farming systems intensify using an increased labor supply, productivity of the land is raised, sustainable agroforestry-with livestock systems are extended, and household income sources are diversified and slowly shifted via the market and short-term mobility away from agriculture and toward other economic sectors.

The experience of the 1970s and 1980s suggests that the optimistic scenario is a plausible alternative, given the right policy environment. Its success depends on increased recognition of the potential of indigenous sociocultural systems of land use and household strategies of economic diversification to increase resilience, and on policies that promote resource access and support those local social systems. The consequences of future droughts may also depend on rates of urbanization, growth of the urban informal sector, and capital investment in better favored rural areas. The present policies of governments and international organizations in the Sahel can create conditions that promote or impede the ability of indigenous systems to respond and thus determine the human consequences of future drought.

SEVEN HUMAN SYSTEMS

This section distinguishes seven human systems that may be affected by, and respond to, global change: individual perception, judgment, and action; markets; sociocultural systems; organized action at the subnational level; national policy; international co-

operation; and global human systems. It briefly surveys current knowledge and ignorance about the responses of each system and the relationships between them and identifies broad areas in which additional research is needed. It also outlines particular research activities and needs within these areas.

I NDIVIDUAL P ERCEPTION , J UDGMENT , AND A CTION

The human consequences of global change begin with the individual. Individuals notice the effects of change and either make adjustments or not. Individual behavior is critical in three quite distinct ways: individual judgments and choices mediate responses in all human systems because decision makers begin with inputs from individuals, whether themselves or their advisers. The consequences of global change often depend on the aggregation of the uncoordinated actions of large numbers of individuals. And individual behavior can be organized to influence collective and political responses.

Individual Judgment and Choice

Responses to global changes presuppose assessments of "what is happening, what the possible effects are and how well one likes them" (Fischhoff and Furby, 1983). 12 Scientists, government officials, and other citizens make such assessments when they consider the responses they may make or advocate. Knowledge about human judgment and decision is therefore relevant to understanding responses to global change.

Normative decision principles, such as those of cost-benefit analysis or mathematical decision theory, are limited in their usefulness by the fallibility of the individuals who try to implement them (Fischhoff, 1979); they are even more imperfect for estimating the behavior of people who are not trying (Fischhoff et al., 1982). Past research on human judgment and decision has clarified many differences between decision theory and actual decision making (Kahneman et al., 1982); some of these are reflected in human responses to natural hazards (Saarinen, 1982; Slovic et al., 1974).

Behavioral decision research demonstrates that most people have difficulty comprehending the very low probabilities assigned to environmental disasters (Slovic et al., 1977; Lichtenstein et al., 1978), estimating the probability of natural events that they rarely experience (Slovic et al., 1979), interpreting uncertain knowledge, and making connections between events and their actual causes.

Moreover, it is difficult or impossible to understand unprecedented events and therefore to make wise choices between mitigating them and adapting to them. One result is that lay people frequently perceive environmental hazards differently from specialists (Saarinen, 1982; Fischhoff and Furby, 1983; Gould et al., 1988; Fischhoff, 1989; Kempton, 1991). Little direct knowledge exists, however, on perceptions of climate, climate change, or other aspects of global change (Whyte, 1985; Kempton, 1991; Doble et al., 1990).

Behavioral research also raises questions about expert judgment. Expert analyses, such as represented in general circulation models of climate, inevitably rely on judgment, and judgment becomes more unreliable when the models move into a future different from any past experience. Faith in expert judgments rests on the analysts' success in identifying all the relevant variables and measuring them and their interrelations. Psychological research suggests that people, including technical experts, "have limited ability to recognize the assumptions upon which their judgments are based, appraise the completeness of their problem representations, or assess the limits of their own knowledge. Typically, their inability encourages overconfidence" (Fischhoff et al., 1977; Kahneman et al., 1982). Overconfidence is most likely to affect expert analysts when they lack experience testing their predictions against reality—an inevitable characteristic of predictions about unprecedented events (Fischhoff, 1989). Other kinds of systematic error may also affect experts. For instance, in water resource management and other fields in which average climate parameters are used as a basis for decision, experts seem to exhibit a "stability bias," a tendency to underestimate the likelihood of extreme events (Riebsame, 1987; Morrisette, 1988).

Careful analysts also sometimes overlook or underestimate the likelihood of some possible combinations of events, as they did in a famous assessment of the likelihood of nuclear power plant failure in the 1970s (Nuclear Regulatory Commission, 1978). Little is known about how individuals or groups formulate alternative action plans when faced with a problem, such as responding to a global environmental change. In particular, little is known about what facilitates or impedes creative generation of options, or how vested interest or attachment to the status quo may blind individuals or groups to available options.

Research Needs Research on what and how nonexperts think about particular global environmental problems can help estimate how individuals will respond to new information about the global

environment and identify their information needs. This research should address particular beliefs about global change as well as how people evaluate probabilistic and uncertain information and how they combine multiple bits of information from experts, mass media accounts, and personal experience (e.g., with recent weather or air pollution events) to form their judgments about the extent and seriousness of global environmental problems. Such research will require both intensive methods of interaction with informants and survey methods.

Research effort should also be devoted to studying the expert judgment of environmental analysts about global change. This research should address such questions as: Does professional training encourage or discourage particular misperceptions? Does it lead purportedly independent experts to share common preconceptions? How well do the experts understand the limits of their knowledge? Do estimates of the human effects of global change take into account feedbacks among human systems? In analyses of possible responses, what responses are likely to be omitted? To whom do experts turn for analyses of feasibility of responses? What implicit assumptions about human behavior guide the analyses? With preliminary answers to such questions, it is possible to estimate the sensitivity of analyses to variables that affect expert judgment and therefore to make better informed interpretations of these judgments.

Aggregated Individual Responses

The consequences of global environmental change often depend on the aggregated responses of very large numbers of individuals. The example of U.S. energy conservation shows the effect of millions of decisions to buy more fuel-efficient automobiles, reset thermostats, and reinsulate buildings; millions of consumers also drove down sales of aerosol cans when the news got out that they were releasing CFCs harmful to the ozone layer (Roan, 1989). Action to block UV-B radiation from the skin of a billion light-skinned people would similarly take many discrete actions by each of them.

As U.S. energy conservation efforts demonstrate, such individual actions are multiply determined. Financial considerations motivate action, but structural constraints limit action (for instance, not owning the home one would like to insulate); personal attitudes and values increase the likelihood of taking actions that fit the attitudes, subject to the other constraints; specific knowledge

about which actions would produce desired effects is helpful, but people often fail to seek it out or mistrust the information available (for reviews of relevant research, see Katzev and Johnson, 1987; Stern, 1986; Stern and Oskamp, 1987). Knowledge has been developed about the conditions under which individuals respond favorably to information (Ester and Winett, 1982; Dennis et al., 1990) and incentives (Stern et al., 1986a) in the context of residential energy conservation; more limited research has been done on other individual actions relevant to global environmental changes.

Research Needs At least three kinds of research should be pursued further to improve understanding of how individual behavior may be significant in response to global change. First is empirical research on the actual responsiveness of behavior to interventions believed to affect it. Energy conservation programs have often produced less than the predicted effects—but as already noted, the responses have been highly variable. For studying possible interventions to mitigate or adapt to global change, pilot studies and controlled evaluation research are particularly important (for a discussion of issues of method in the energy conservation context, see Stern et al., 1987).

Second, new research is warranted to determine the relative contributions and interactions of the various influences on particular individual behaviors implicated in global change (e.g., Black et al., 1985). This research should be interdisciplinary because, in most instances, behavior is jointly determined by technical, economic, psychological, and social variables in ways that are likely to differ as a function of the behavior and the societal context.

Third, research should be conducted to build an improved interface between behavioral studies of resource use and formal models, which are guided mainly by economic assumptions. Empirical analysis of the behavioral processes underlying descriptive categories such as price elasticity, implicit discount rate, and response lag is likely to add to understanding of human responses to price stimuli and government intervention, and also to encourage needed dialogue between economically and psychologically oriented analysts of consumer behavior (Stern, 1984, 1986).

Individuals as Social and Political Actors

Individuals, appropriately mobilized, can be powerful actors at the community and national levels. Individual perception and judgment determines support for social movements, such as the

environmental movement, that affect human response by linking individuals to the concerted actions of government and industry. Those actions, in turn, influence individual behavior both directly and through their effects on markets. Individual reactions, in the aggregate, determine the public acceptability of policy alternatives being considered for response. And secular changes in individual attitudes and values, such as about the importance of material goods to human well-being, may have great effects on the long-term response to global change.

Past research has investigated the correlates of environmental concern and related attitudes (e.g., Borden and Francis, 1978; Van Liere and Dunlap, 1980; Weigel, 1977) and tracked the rise of postmaterialist values in the United States and other Western democracies (Inglehart, 1990). Such attitudes have been strong and persistent in many countries since the 1970s. Other research has been devoted to the rise of the environmental movement and to its objectives and tactics (see below).

Research Needs There are important gaps in the literature. New research should carefully assess alternative hypotheses about the links between individuals' values and attitudes and their representation in the activities of environmental movement groups and other institutions involved in response to global change. For instance, the view that environmental organizations reflect widespread attitudes should be tested in the global context against other views, for instance that social movement activists act as entrepreneurs, with their own interests separate from those of the public they claim to represent (e.g., Touraine et al., 1983; Rohrschneider, 1990).

Future research should also address the bases of environmental concern. Such concern may derive from a new way of thinking about the relationships of humanity to the planet (e.g., Dunlap and Van Liere, 1978) or from concern about harm done to people, such as those indirectly affected by market transactions and those yet unborn (Dunlap and Van Liere, 1977; Heberlein, 1977; Stern et al., 1986b). Outside the U.S. context, yet other bases of concern may predominate. For instance, in several Soviet republics, the environmental movement of the late 1980s expressed demands for autonomy by smaller nationality groups against the dominant Russians. On another dimension, environmental concern may derive from personal experience or secondhand accounts in the mass media. The source of concern may determine the conditions under which people become aroused about a global change or recep-

tive to policies that take meaningful action but require additional costs. The determinants of concern are likely to vary with the environmental problem, the country, and characteristics of the individual, so the research should be comparative between countries and environmental problems of different kinds.

One of the most likely consequences of global change will be effects on the prices of important commodities and factors of economic production in local and world markets. As a result, uncoordinated human responses will be affected greatly by markets. According to economic theory, producers and consumers respond to changing relative incomes, prices, and external constraints, so that, if the market signals are allowed to reach individuals and market prices include all the social costs and benefits of individual actions, the responses will be relatively rapid and efficient.

Markets allow for many forms of uncoordinated adjustment, as the example of climate change illustrates. People may rapidly alter patterns of consumption (e.g., substitution of water skiing for snow skiing) and production (e.g., relying on snowmaking equipment rather than natural snowfall). Over the longer run, societies may respond, in the case of unfavorable climatic developments, with the migration of capital and labor to areas of more hospitable climates. Structures tend to retreat from the advancing sea, people tend to migrate from unpleasant climates, and agricultural, sylvan, and industrial capital tend to migrate away from lands that lose their comparative advantage. In addition, technology may change, particularly in climate-sensitive sectors such as agriculture and building.

However, the conditions that economic theory specifies for efficient adjustment are not generally met in the case of the global environment (Baumol and Oates, 1988). In three important respects, existing markets do not provide the right signals (in the form of prices and incomes) of social scarcities and values. And in addition, as already noted, the participants in markets do not always behave as strict rules of economic rationality predict.

Environmental externalities of economic activity, that is, effects experienced by those not directly involved in economic transactions, are not priced in markets today. Someone who emits a ton of carbon into the atmosphere may produce great damage to the future climate but does not pay for the damage: effects that

have no price may be treated as if they have no value. Similar problems arise with the externalities of deforestation, CFC emissions, and other environmental problems. Economic theory recognizes that when there are significant externalities, uncoordinated responses will be inappropriate because the market does not transmit the right signals. An additional problem concerns making tradeoffs when each response option produces different externalities (Fischhoff et al., 1981; Bentkover et al., 1985; Mitchell and Carson, 1988; Fischhoff, 1991).

The market mechanism is overridden at times, either by political systems (such as when countries set the prices of oil or coal well below or above world market levels); or because custom and tradition determine property rights in a way that precludes the emergence of markets, as in the case of water allocation in the western United States. In such cases, individuals are either not faced with prices at all or are faced with prices unrepresentative of true social scarcities, and their uncoordinated behavior will not achieve the rapid and efficient adjustments characteristic of free markets.

Discount rates in markets, such as interest rates, reflect a social time preference for the present over the future that does not correspond to social valuation of the distant future reflected in concern about problems of global change (Lind, 1986). For events a century in the future, a discount rate that is, say, 3 percent per annum higher than true social preference implies that the future events are valued at only one-twentieth (that is, 1.03-100) of their appropriate value. Market interest rates may be too high to reflect this generation's concerns about the future of the environment; vigorous debate exists about whether the concept of discounting is even moral when human life is at stake (MacLean, 1990). Uncoordinated decisions following such a discount rate undervalue future threats and opportunities.

Economic theory suggests prescriptions for government action when market signals do not correspond to social values. The goal usually considered most important is to get the environmental impacts reliably translated into the price and income signals that will induce private adaptation. But it is difficult to arrive at the "correct" prices because so many of the impacts of global change are unknown or uncertain and because the appropriate values of future events are unlikely to be the same from all generational vantage points and resource endowments (Lind, 1986; Pearce and Turner, 1990).

Economists have suggested some approaches to the problem of developing well-functioning markets to guide responses to global

change (for some examples, see Pearce and Turner, 1990 and Dasgupta and Heal, 1979). Theory suggests that governments intervene with policies that meet at least one of these criteria: (1) they have such long lead times that they must be undertaken now to be effective; (2) they are likely to be economical even in the absence of global change; or (3) the penalty from waiting a decade or two to undertake the policy is extremely high. These criteria suggest four kinds of intervention, which we note here.

Government may encourage quasi-market mechanisms before shortages occur. For example, to ensure that water will be efficiently allocated if climate change affects its availability, governments might introduce general allocational devices, such as auctions, to dispatch water to the highest-value uses. The same approach might be applied to allocate land use near sea coasts and in flood plains and to control pollution by auctioning pollution rights. Governments might also support systems of risk-adjusted insurance for flood plains or hurricanes or international climate insurance. These quasi-market mechanisms have both the advantages and the disadvantages of the market. They make allocations efficiently but tend to undersupply goods needed by those who do not participate effectively in the markets, such as people outside the geographical boundaries of a quasi-market, who may receive polluted air or salinated water.

Government may support research and development on inexpensive and reliable ways of slowing or adapting to global change. Research on adaptation is undersupplied by markets because inventors cannot capture the full fruits of their inventions. Research on mitigation technologies that will slow global changes are even more seriously undersupplied in markets, because not only can inventors not collect the fruits of their efforts, but also the fruits, such as preservation of climate, are unpriced or underpriced in the market.

International agreements may provide for international adaptation strategies, such as improved international markets, which allow migration of labor and capital over a greater geographical range than national markets.

Governments may promote needed knowledge and collect and distribute data about global change, to enable rational response. It is difficult for people to mitigate or adapt if they do not understand what is happening or the costs of the available responses and of inaction; costs of adaptation will be reduced to the extent that managers, diplomats, and voters are well informed about well-established scientific results.

Research Needs Although the above market-oriented response strategies are strongly supported by economic theory, knowledge is weak about how they may be effectively implemented. Three lines of research into markets can add to understanding of the available response strategies.

First, empirical studies are needed of the implementation of quasi-market mechanisms for adaptation to global change, to determine how particular mechanisms work in particular social and political systems. For instance, systems for auctioning emission rights can be made infeasible by political opposition, subverted by fraud, undermined by political decisions, or otherwise altered from their theoretically pure operation (Tietenberg, 1985, explains the principle in the case of local air pollution; application to global change would be more difficult). Retrospective and prospective studies of the operation of such mechanisms can illuminate the problems that arise in implementation and assess the actual, as opposed to theoretical, effects of such mechanisms on equity and efficiency. Such assessments should compare quasi-market mechanisms to available regulatory mechanisms, as each actually operates (see the section below on national policy).

Second, studies of the valuation of global environmental externalities are critically important to address several key questions. For instance: To what extent can knowledge or technology be substituted for the outputs of environmental systems, thus making those outputs less indispensable? Is such substitution desirable? How can the ''services'' produced by the natural environment be included in economic accounting systems, such as national income accounts? How can the producers and recipients of externalities arrive at a common valuation if one side is disadvantaged in financial resources, and therefore in the ability to participate in markets or quasi-markets? How do people value, and make tradeoffs between, different kinds of externalities? How do different actors value the effects of human interventions in the environment and make tradeoffs between effects? (Some of these questions are addressed in work by Mitchell and Carson, 1988, and Nordhaus, 1990.)

Third, studies of social discount rates are needed, especially to estimate preferences concerning the future environment so they can be included in evaluations of global environmental change (e.g., Lind et al., 1986). Many believe that market discount rates are too high to accurately represent the social value of the future environment, although this value is unknown.

S OCIOCULTURAL S YSTEMS

Between the uncoordinated activities of individuals and the formally organized activities of governments and international organizations lie the oldest forms of social organization: families, clans, tribes, and other social units held together by such bonds as solidarity, obligation, duty, and love. These sociocultural systems have undergone considerable change throughout human history, yet informal groups connected by these bonds still exist and the bonds still influence behavior independently of governments and markets. Sociocultural systems are important in terms of global change in two ways. Some long-lived social units, whose survival may be threatened by global change, have developed ways of interacting with their environments that may be adaptable by others as strategies for response. Also, informal social bonds can have important effects on individual and community responses to global change and on the implementation of organized policy responses.

Indigenous Sociocultural Systems of Adaptation to Environment

Indigenous peoples that were not tightly integrated into world markets have developed technological and social adaptations that often maintain their subsistence in reasonable balance with the local environment. The adaptations of Sahelian peoples to an environmental regime of recurrent drought is one example. A parallel example can be found in the indigenous economic systems on the Amazon, which for at least 500 years have used the ecosystem's material in ways that do not threaten its long-term productivity (Hecht and Cockburn, 1989). The Amazon's indigenous people are a major repository of practical environmental knowledge about sustainable use of resources (Moran, 1990; Posey, 1983). Slash-and-bum cultivation with adequate fallow periods allows for the recovery of vegetation in tropic moist forests (Uhl et al., 1989), attracts game animals to crops (Linares, 1976; Balée and Gély, 1989), and provides a well-balanced, varied diet (Baksh, n.d.). Local agroforestry systems, which combine "the production of crops including tree crops, forest plants and/or animals simultaneously or sequentially on the same unit of land" (King and Chandler, 1978), mimic tropical ecosystems, protecting the soil from leaching and erosion while replicating the natural succession of plant growth over a period of years, and are a model for modern systems of agroforestry. Some such systems can give per

hectare yields over five years roughly 200 percent higher than systems established by colonists and 175 times that of livestock (Hecht, 1989a:173).

Agricultural systems based on indigenous models can be profitable in a market economy. Japanese colonist smallholders in the Amazon have created complex systems that prevent soil degradation and tolerate soil acidity and aluminum toxicity better than annual crops. These systems involve polycultures of mixed perennial and annual crops that are transformed, over time, into polycultures of mixed perennials. Commercial quantities of black pepper, cacao, passion fruit, rubber, papaya, eggs, and pumpkins and other vegetables are produced (Subler and Uhl, 1990). Into this sustainable, intensive agroforestry system, the Japanese farmers often incorporate fish culture and chicken and pig production and use waste or refuse from one operation as inputs to other operations (Uhl et al., 1989).

The knowledge about environmental adaptation resident in indigenous social groups depends, of course, on the survival of these groups. Development strategies that destroy the forests can undermine the ability to mitigate or respond to global change by threatening local sociocultural systems based on sustainable, noninvasive strategies of using the land. In the Amazon, the newly expanding, extensive land uses are not compatible with indigenous Indian systems of gathering, long-fallow cultivation, fishing, and hunting and also threaten the subsistence of some 2 million small-scale extractors who collect rubber, nuts, resins, palm products, and medicines while practicing small-scale farming and foraging. Current issues in the Brazilian policy debate that will affect the viability of indigenous groups include the implementation of reserves on which these groups collectively determine resource exploitation (Hecht and Cockburn, 1989), institutions governing the enclosure of public land for unrestricted private uses, and various types of park or biosphere areas with protected wilderness and some degree of zoned multiple use (Poole, 1989:43).

Indigenous sociocultural systems that have adapted to highly variable environments may offer lessons for improving the robustness of social systems to environmental changes outside of past experience. The adaptation in the Sahel points to the importance of diversified sources of cash and subsistence in allowing local groups to adapt to environmental change with limited human cost. An instructive counterexample may be the American Great Plains, where a new generation of settlers between the 1890s and 1920s developed an agricultural system poorly adapted to the area's vari-

able rainfall patterns. The limited adaptability became obvious in the Dust Bowl period of the 1930s. The results included large-scale out-migration and the development of a national system of governmental supports for regional agriculture that encouraged the remaining farmers to further expand their use of limited water supplies. Some analysts believe these changes brought the farmers' adaptability without continued outside assistance into even more serious question (Worster, 1989). Other recent research, however, argues that the serious drought of the 1950s did not have devastating effects and suggests that a recurrence of the climate of the 1930s in the Great Plains would have little effect on the region's agriculture (Rosenberg et al., 1990).

Research Needs Research on intensive, sustainable agricultural systems can help identify and evaluate viable alternatives to development strategies that have resulted in deforestation and land degradation in the tropics. Such research can help develop strategies that may provide subsistence and cash for rural populations but that do not afford the high returns to labor and to speculative activities of unrestricted, extensive land use (Moran, 1990).

Research on systems of land use in variable environments can help identify the characteristics of some of these systems that allow them to take environmental change in stride. Such research can identify anticipatory policies that may enable local or regional social systems to withstand the local effects of global environmental changes at low cost, with limited demands on disaster response systems.

Social Bonds and Responses to Environmental Change

Individual behaviors in response to global change are also affected by informal social influences. People imitate individuals they like or respect, follow unwritten norms of interpersonal behavior, and preferentially accept information from sources they trust (Darley and Beniger, 1981; Brown, 1981; Rogers, 1983; Rogers and Kincaid, 1981).

Such influences are significant factors in social response to natural disasters, particularly those that strike quickly and with little warning, such as floods and major storms (White, 1974; White and Haas, 1975; Burton et al., 1978; Riebsame et al., 1986; Whyte, 1986). Studies of community responses to disaster show that family and acquaintance groups and community organizations are often the focus of behavior (Dynes, 1970, 1972), and that spon-

taneous improvisation at the local level—often by nongovernmental groups—has been a key to effective response (Barton, 1969; Quarantelli and Dynes, 1977). These findings are relevant to global climatic change in that the consequences of such change are likely to include a shift or increase in the incidence of just such natural disasters.

Informal social links are also significant influences on the acceptance of mitigation strategies, such as energy conservation programs aimed at individuals and households (Stern and Aronson, 1984). Adoption of new, energy-efficient technology tends to follow lines of personal acquaintance (Darley and Beniger, 1981), and participation in government energy conservation programs is higher when the program takes advantage of personal acquaintanceships and local organizations with good face-to-face relations with members of the target group (Stern et al., 1986a).

Research Needs Efforts to develop policy responses in anticipation or response to global change will benefit from knowledge of sociocultural systems of social influence. Research efforts can profitably focus on understanding the social networks, norms, and influence patterns of groups that are highly likely to suffer from anticipated environmental change, so that policies can be designed to work with rather than against these lines of influence. Policy studies should focus on ways to directly involve affected groups, and should compare implementations of the same policies with and without such efforts.

O RGANIZED R ESPONSES O UTSIDE G OVERNMENT

Three kinds of social actors other than governments may make significant, organized responses to global change: communities, social movements, and corporations and trade associations. These collective actors form a vital link between behavior at the level of individuals, firms, and households and at the level of institutions and nations.

Communities

A community is more than a shared place of residence. It is also a unit in which people earn their living, engage in political activity, raise their children, and carry out most of their lives. Community responses to the stresses of environmental change occur both in the uncoordinated ways discussed in the previous

section and through organized activity. Decades of research on economic development in rural areas suggests that the full impacts of major social changes, including those that may be induced by environmental change, can be understood only by considering the effects of such changes on communities, as well as on individuals and institutions (e.g., Field and Burch, 1988; Machlis and Force, 1988; Machlis et al., 1990).

Communities are likely to respond in different ways to the local impacts of global environmental change. Some communities are sufficiently diverse to provide valuable buffers against hardship as individuals and households share resources. But if all members of the community use the same environment in similar ways, no such buffering is possible. Traditional relationships and patterns of action, tension, and rivalry within a community may help the community through crisis, or may prevent organized action that would help the community cope with or take advantage of local changes. And if local manifestations of global change disrupt traditional patterns of community life, they generate stress and conflict that can become violent.

Of course, the character of community life continues to change in much of the world. With the rapid growth of urban and suburban areas in the developed and especially the developing world, the historical links among home, polity, and economy are greatly weakened. The spheres in which individuals and households act become more disjunct and less well integrated. Global environmental change may increase the pace of this historical trend if it makes rural agricultural life more difficult and thus increases the migration to urban areas, with consequences for the ability of communities, particularly in the Third World, to withstand further environmental change.

Research Needs Research is needed on those characteristics of communities that affect their organized responses to global change. For example, in the United States, the spatial character of suburban communities is a significant barrier to increased use of public transportation. Yet some suburban communities and small towns have been vigorous in their implementation of environmental and energy and water conservation policies (Dietz and Vine, 1982; Berk et al., 1980; Vine, 1981). The response of those communities seems to be greater than would be expected from aggregated simple self-interest or the technical response to changes mandated by policy. The community amplifies individual action, perhaps by creating a sense of identity and trust that overcomes the usual

collective goods problem. Especially in the less-developed world, effective community response may depend on the community's access to a variety of resources that can be used to dampen adverse changes in any single resource. In addition, adaptation by individuals and households may be conditioned by the diversity and flexibility of the community, which are in turn affected both by the natural environment and the local political economy, history, and culture. Research is also needed on the conditions controlling the differential effectiveness of environmental and energy programs in different communities.

Social Movements

Environmental movement organizations have been major actors in debating national and even international responses to global change (also see the section below on national policy). The broad awareness that global changes are occurring is in large part due to various national environmental movements drawing attention to the growing body of scientific evidence on the subject.

Most of the national activity of environmental movement organizations is intended to change public policy. How environmental groups influence policy depends on the political context in which they operate, and in particular on the relationship between the movement and political parties. In political systems in which it is difficult to achieve participation via a small party, such as the United States, movements have only loose alliances with political parties. In systems where small parties can play a serious role in influencing policy, the movements either form tight alliances with parties or act as parties in themselves. These structural differences affect movement strategy and have produced some sharp differences in how environmental problems are conceptualized. The ways political structure affects the political impact of the environmental movement on policy have not been studied in enough detail to offer generalizations.

Whatever their relation to political parties, environmental groups usually find themselves in conflict with corporations, trade associations, and often with government officials. Each side brings a different mix of resources to the conflict. In the United States, environmental groups seem to have a high degree of public support and strong legitimacy with other actors in policy debates (Dietz and Rycroft, 1987). Corporations and their representatives have far greater financial and personnel resources, but less public support and less legitimacy within the policy system. Govern-

ment falls between the two. The difference in resources means that each group will struggle not only over the substance at issue, such as a specific policy, but also over the definition of the problem and the kinds of resources that are legitimate for resolving the problem (Dietz et al., 1989). The difference in resource distribution has typically led industry to favor heavy reliance on scientific analyses and technologically driven policies, and led environmentalists to be more skeptical of those alternatives and inclined to favor source reduction and infrastructure changes.

Modern environmental groups play an important role in shaping public values and consciousness. Indeed, some students of the movement have suggested that its primary goal is to change ways of thinking rather than specific political choices (Cohen, 1985; Eder, 1985; Habermas, 1981; Offe, 1985; Touraine, 1985; Touraine et al., 1983). The rise of "green" ideologies in the United States, Western Europe, and throughout the world seems to reflect changes in consumer preferences and lifestyles that may have important implications for individual, household, and community response to global change (Inglehart, 1990).

Research Needs A number of important questions need to be answered about the role of the environmental movement in responses to global change. How do the strategies pursued by environmental movements in both the developed and less-developed nations influence the character of national policy? What impacts do these influences have on the ability to reach international accords? How does environmentalism interact with scientific research on global change, and what could be done to produce better interactions? How much change in individual ideology is brought about by the environmental movement, and how do these changes affect the behavior of individuals, households, communities, and other actors? What is the likely character and influence of the environmental movements that are emerging in Japan, Eastern Europe, and less developed nations and what role will they have in shaping national and international response?

Corporations and Trade and Industry Associations

Corporations and trade and industry associations are major actors shaping response to global change. Just as the environmental movement translates public concern into political action and in turn shapes public perceptions and actions, corporations and trade associations translate the interests they represent into political

positions and also educate those connected to them. As already noted, these groups come to the policy arena with very different resources than environmental groups and, in general, tend to favor different methods for analyzing environmental problems and different strategies for solving them (Dietz and Rycroft, 1987; J.R. Wright, 1990).

Research Needs The relationships of corporations and trade associations to national policy systems, critical for understanding policy response, are discussed in the next section. The internal aspects of these collectivities, however, are little studied. Corporations communicate with each other, and trade associations are influential in shaping the response of corporate members, two processes that shape the policy positions of the business community. Research is badly needed on how corporations and trade associations attempt to communicate internationally about global environmental issues with other groups representing the same industries.

N ATIONAL P OLICY

Nation-states help determine the consequences of global change through their essential role in international agreements and by national policy decisions that affect the ability to respond at local and individual levels. This section focuses primarily on two issues: differences between nations in their environmental policies and the policy process.

National Differences in Environmental Policy

National environmental policies vary in part because of different public attitudes. People around the world have shown concern with the environment, but the intensity and focus of interest have varied from country to country. Some observers claim that during the early 1970s, environmental issues were much more politically salient in Japan and the United States than they were in Europe; during the 1980s, the reverse has been true (Vogel, 1990). Such variations may be a function of national economic performance, actual environmental quality, or national political cultures. The focus of environmental concern in Japan has been claimed to be on the protection of public health, while in Germany the protection of nature has been accorded much higher priority, with the United States and Great Britain falling some-

where in between (Vogel, 1990). These differences, which may be more or less stable over time, are likely to have important implications for different nations' responses to various kinds of global environmental issues.

Policies also vary because each nation's political system responds to public concerns in its characteristic way. Within democratic nations, many political features vary. Nongovernmental organizations concerned with environmental improvement are not equally well organized in all countries. Citizens of different nations display different propensities to join voluntary organizations concerned with environmental improvement, and these organizations do not have similar access to the policy process everywhere. The United States, with its constitutional system based on the separation of powers, provides nongovernmental organizations with substantial opportunities to shape public policy through access to the courts and the national legislature. By contrast, more centralized political systems, such as France and Japan, severely restrict participation by citizens' groups. Parliamentary systems that have proportional representation, such as in Germany, provide access to the political system by facilitating the formation and representation of political parties committed to environmental improvement (see Parkin, 1989).

Policy systems also vary in the response of major affected interests, particularly those of business. Most environmental problems, domestic as well as global, require substantial changes in what firms produce and how they produce it. To the extent that these changes increase costs, businesses are likely to oppose them and the changes are unlikely to occur. Business resistance can be reduced if new technology enables firms to behave in ways that are environmentally benign without increasing their costs, if consumers develop a "green" consciousness that opens new markets, or if government offers subsidies. As a rule, environmental policies are more likely to be effectively implemented to the extent that investors and managers in some industries and firms believe they can benefit financially.

These issues extend beyond business. Environmental regulations do not simply impose additional burdens on producers; they also affect the relative welfare of consumers, employees, and taxpayers. These burdens may be primarily nonmonetary or monetary, concentrated or dispersed, and relatively visible or invisible, but in all cases they have important political consequences. There is a relevant body of research on how interest groups respond to different kinds of expected burdens and benefits, at least

in the United States and a few other countries (Leone, 1987; Meiners and Yandle, 1989).

Environmental policy systems vary in many ways in their approaches to regulation (e.g., Tarlock and Tarak, 1983; Mangun, 1979). Regulations may control emissions at the source, by establishing environmental quality standards, or by establishing exposure standards. Each strategy has various strengths and weaknesses (see Haigh, 1989). Environmental regulation can be coordinated by a single regulatory body or dispersed among a variety of regulatory authorities; relatively centralized in the national government, as in Great Britain, Japan, and France, or administrated primarily by local governments, as in the Federal Republic of Germany. Regulation can be anticipatory, requiring firms to get permission before they can act, as with mandatory environmental impact assessments, or may take place after the fact. And there are different national styles of regulation (Vogel, 1986). The United States has developed an adversarial regulatory style, in which government establishes ambitious and highly specific standards and frequently tries to impose legal penalties for noncompliance. Great Britain, by contrast, uses an approach to regulation characterized by more flexible standards, modest goals, very infrequent use of legal penalties, and restricted participation by the public and environmental groups.

Scientists and scientific evidence play very different roles in different countries' environmental policies. The United States is unusual in providing opportunities for diverse groups of scientists to affect regulatory policies. By contrast, participation by scientists in Europe is more likely to be confined to official channels. The United States is also unusual in having regulatory decisions tied by statute to the outcomes of risk analyses. Thus, it is sometimes easier to have a product or production process banned or restricted in the United States than in most other capitalist nations (see, e.g., Brickman et al., 1985).

Research Needs Most of the sources of variation mentioned apply not only to environmental policies but also to national-level policies in many other areas that can have significant effects downstream. Research is needed to assess the effects of national macroeconomic, fiscal, agricultural, energy, economic development, and science and technology policies on global change and on the ability to respond to global change. These effects are much less well researched than the effects of environmental policy.

Cross-national research comparing the determinants of national

environmental policy, focused especially on responses to global change and on the sources of policy differences between countries, is also needed. This research should assess the effects of influences such as public opinion, environmental movement organizations, and various organized interest groups, as well as structural features such as democratic versus nondemocratic politics, market versus centrally planned economies, relative wealth, scientific and technical resource base, and position in the world political-economic system (studies of this type, not focused on responses to global change per se, include Brickman et al., 1985; Jasanoff, 1986; Vogel, 1986; and Jasper, 1990). Such research can help clarify the kinds of policy options that are viable in different countries, which is a factor in reaching and implementing international agreements. In particular, it is important to understand the conditions under which nations enact policies promoting the development of environmentally benign technologies because such development, while it could produce large benefits on a global scale, is often unlikely to come from the private sector because of the difficulty of appropriating profits.

Research should also assess the impact of environmental regulation and alternatives to regulation cross-nationally and across policy questions to clarify how, why, and under what circumstances different regulatory or other strategies work in different policy settings. Such research should proceed despite the lack of clear standards for comparing the effectiveness of the environmental policies of different governments. Every indicator has both strengths and weaknesses. For example, emissions and environmental quality are affected by many factors other than policy, including topography, the nature of industrial production, and the rate and location of economic growth. Likewise, expenditures on abatement by industry are an imperfect measure of the effectiveness of regulation because they may or may not represent a net economic burden. The useful literature on policy compliance and effectiveness is largely confined to a handful of countries and policies (e.g., Bardach and Kagan, 1982; DiMento, 1989).

Finally, research should compare the institutions used in different countries to manage conflict over environmental policy. These institutions are both formal (e.g., legislative and regulatory proceedings and court decisions) and informal (e.g., lobbying, use of publicity in the mass media), and they deal with substantive disagreements, formal procedures, and disagreements about the nature of knowledge about global change and the likely impacts of policy choices. Distinctive national systems of conflict manage-

ment can be identified and compared; each probably generates characteristic patterns of conflict and characteristic difficulties in decision making.

The Environmental Decision-Making Process

The consequences of global change depend on decisions made in government agencies and other large organizations. Knowledge about the decision process in such organizations is therefore potentially relevant to responses by both governmental and nongovernmental organizations. Specialists on decision processes, a field that makes no sharp distinction between governmental and other complex organizations, typically distinguish analytically among phases of the process, such as understanding the phenomena, identifying viable options, and selecting an alternative.

Government agencies involved in responding to global change rely on information from experts to gain understanding, but they must make it useful to their leaders, who are almost always non-experts, and must interpret the conflicts between, and uncertainty within, expert judgments. There is a general body of literature on the ways government agencies and other large organizations acquire and process expert knowledge (e.g., Lindblom and Cohen, 1979; Weiss and Bucuvalas, 1980) and on the inherent problems of informing nonexpert decision makers about uncertain and disputed scientific knowledge (National Research Council, 1989b).

Organizations can generally identify a large number of options, but they tend to funnel information to narrow the universe of issues or action alternatives presented to leaders (March and Olsen 1989). Similarly, not all options known to a society reach its legislative agendas (e.g., Kingdon, 1984). Among the factors involved in getting environmental issues on political agendas arc mass media coverage of disastrous or telegenic events and threats, of dread consequences such as cancer, danger to children and future generations, the characteristics that increase perceived seriousness of risks among most citizens (Mazur, 1981; Sandman et al., 1987; Rosenbaum, 1991). Government action on environmental hazards is typically driven by crises, with major events evoking bursts of legislation (May, 1985; National Research Council 1987). It is less clear, however, how particular response options, get on the agendas of government agencies or other organizations

Decisions within government agencies and other large organizations are affected by standard operating procedures, preassigned divisions of labor, accounting systems, organizational cultures

bureaucratic politics, organizational hierarchy, bargaining and negotiation processes, leadership practices, and the control of information by constituent individuals and subunits with goals only partly coincident with those of the organization as a whole (Seidman and Gilmour, 1986; March and Olsen, 1989). Decisions are influenced by relationships between organizations, for example, in international environmental agreements, interagency negotiations, lobbying coalitions, and even large industrial firms that must weigh the positions of their marketing, manufacturing, engineering, and legal departments in deciding whether to change to a more environmentally benign manufacturing process. Decisions are also affected by the structure of institutions—the systems of rights and rules that constrain the actions of individual parties. Examples include the effects of such institutions as markets for land and energy, land tenure systems, the law of property rights and torts, representative government, and international regimes (discussed in the next section).

Research Needs The organizational decision-making perspective points to a number of areas in which the general concepts in the field might be usefully applied to organizational actions affecting response to global change. For instance, informative studies could be done on how organizational understanding of environmental issues develops; how intraorganizational factors affect the responses of corporations, government agencies, and national political systems to global change; and how bargaining, rivalries, informal norms, and other processes of influence between organizations affect organizational responses to global change. An area of more pointed interest is the comparative study of environmental decisions in different institutional contexts. To gain understanding of the consequences of global change, it is important to understand the effects of different systems of land tenure on deforestation, of different national regulatory systems on the control of atmospheric pollutants, and of different systems of property rights in subsurface resources on policies to limit extraction of fossil fuels.

I NTERNATIONAL C OOPERATION

Sustained international cooperation is one essential element in the overall human response to global environmental changes. It is essential because efforts to cope with some large-scale environmental changes such as ozone depletion and global warming seem

doomed to fail if some of the major national actors do not cooperate. Recent agreements among the advanced industrial countries to phase out the use of CFCs cannot solve the problem of ozone depletion unless some way is devised to persuade China, India, and other developing countries to use substitutes for CFCs in their rapidly increasing production and consumption of refrigerants. The global warming problem is even more complex. Not only is there a need for cooperation between the advanced industrialized states and the major fossil fuel-using states of the developing world, but there is also the problem of controlling other sources of greenhouse gases. These sources are as diverse and widespread as methane-releasing agricultural activity in south Asian rice paddies and North American feedlots and carbon releases from cutting tropical forests in Zaire and Brazil.

Some environmental problems call for international action because activities in one country produce spillover effects or externalities affecting other countries. An example is the emission of airborne pollutants in the eastern United States and Eastern Europe. International cooperation is needed to articulate and apply liability rules or to allow the countries affected by spillover effects to compensate those responsible for the offensive emissions for terminating or redirecting their activities.

Today's concerns with international arrangements focus mainly on mitigating global environmental changes rather than adjusting to them. In the future, however, as global changes become realities, there will be more calls for international cooperation to adjust to the impacts, for instance, by developing buffer stocks of food crops or mechanisms to handle flows of environmental refugees.

International cooperation poses difficult problems, even when all the parties stand to gain from the right agreement. One of the most robust theoretical findings of the social sciences is that rational actors engaging in interactive decision making in the absence of effective rules or social conventions often fail to realize feasible joint gains, sometimes ending up with outcomes that are destructive for all concerned (Olson, 1965; Hardin, 1982). The conditions of international society make the problem more complicated than it is in other situations. The issues are seldom well defined at the start, so that preliminary negotiations may be needed to define them. When unanimity is required, some states can hold the agreement hostage to better terms for themselves. Each country is complex, and bargaining within countries can make international agreements especially difficult (Putnam, 1988). And

the agreement can take second place to more immediate issues in any of the countries involved.

Most observers now believe that the key to solving these collective-action problems is in the creation of international regimes, or more broadly, international institutions (Krasner, 1983; Young, 1989a). Regimes are interlocking sets of rights and rules that govern interactions among their members with regard to particular areas of action. Although most of the research on international regimes concerns economic regimes, interest is mounting rapidly in the study of environmental regimes, particularly the developing regime for the protection of the stratospheric ozone layer (Benedick, 1991), but also other, more geographically limited, international environmental regimes (e.g., Sand, 1990a; Haas, 1990).

The ozone regime exemplifies one model of regime formation, in which a framework convention is followed by a series of substantive protocols in quick succession. Another model sets out substantive provisions in more or less complete form in initial agreements. Cases in point include the 1946 International Convention for the Regulation of Whaling and the 1973 Convention on International Trade in Endangered Species of Wild Fauna and Flora (Lyster, 1985). Additional study is warranted to determine the circumstances under which one or the other of these models is more appropriate.

Most of the research on environmental regimes has so far emphasized regime formation, particularly the determinants of success or failure in forming regimes and the timing and content of successfully formed regimes. This work has highlighted five sets of explanatory variables. One stream of analysis emphasizes structural aspects of the relationships involved in regime formation, such as the number of participants, the extent to which interaction is ongoing, and the nature of the mixed incentives to cooperate and compete (Oye, 1986). Another stream focuses on the role of power relationships, such as the presence of a hegemonic power, that is, an actor possessing a preponderance of material resources (Keohane, 1984:Chap. 3). A third stream emphasizes factors likely to impede or facilitate the negotiation process, such as the extent to which negotiations lend themselves to ''integrative bargaining,'' the thickness of the "veil of uncertainty," the impact of exogenous crises, and the role of leadership (Young, 1989b). A fourth stream emphasizes cognitive variables, such as the role of widely shared ideas (Cox, 1983) or an "epistemic community," that is, an international group of officials and scientists who share

a set of causal beliefs and a set of preferences for action (Haas, 1990). A final stream of research stresses the importance of the international context in providing windows of opportunity for agreements that are blocked at other times by resistances in one country or another.

Research Needs Knowledge is limited on several aspects of international agreement that are particularly relevant to problems of response to global change. One is the effectiveness of institutional arrangements, that is, the factors determining how strongly a regime affects the behavior of those subject to its provisions. Effectiveness is partly a function of implementation which, as at the national level, often leads to outcomes quite different from what a reading of the initial agreement would lead one to expect (Pressman and Wildavsky, 1984). It also depends on the degree to which arrangements are structured so that those subject to the regime comply voluntarily and do not have to be continually monitored and coerced. Finally, it depends on the ability of a regime to persist even after the constellation of interests that gave rise to it has changed or disappeared (Krasner, 1989).

Another area for new research concerns preparatory negotiations, aimed at reaching a common conceptualization of environmental problems. Many international issues that require cooperation are not ripe for negotiation because the issues have not yet been defined in a way suitable for bargaining (e.g., Stein, 1989; Saunders, 1989). This certainly seems to be the case for complex environmental issues, such as would be raised in drafting a comprehensive law of the atmosphere on the model of the law of the sea. National representatives would need first to identify packages of policies they might use to comply and assess the costs of those packages in terms of their interests. The process would be much more complex than establishing limited regimes to deal with ozone depletion or acid rain or establishing a series of regional regimes combined with agreements between regional groups.

A third area concerns the problems of regime formation when the participants are deeply divided. Many global environmental problems involve north-south confrontations in which the wealthy, industrialized states want to limit environmental changes but developing countries see limits as threats to their development. Examples include conflict between the desire to limit carbon dioxide emissions and energy needs in China and India, and between the desire to protect global biodiversity and plans for the use of forests in Brazil and Indonesia. Much needs to be learned,

for example, about the bargaining power of apparently weak players, like China, which can issue credible threats to step up their use of coal or CFCs unless others make it worthwhile for them to desist.

More knowledge is also needed about the role of nonstate actors, such as intergovernmental organizations, environmental movement organizations, and transnational corporations, in the creation and operation of environmental regimes. The involvement of such nonstate actors heralds the emergence of a more complicated international society in which states remain important but share influence with several other types of actors. This change may require more sophisticated conceptualizations of international interactions.

Finally, there is need for better understanding of the relationships between institutions (sets of rights and rules) and organizations (material entities with offices, staffs, budgets, and legal responsibility) (Young, 1989a, b). Organizations, such as the United Nations Environment Programme, have sometimes been important players in regime formation; they are sometimes necessary to manage regimes, although implementation of key rules is sometimes delegated to the member governments. Given the costs of operating international organizations, it is important to have a better understanding of the conditions under which they are necessary, or more effective than alternatives.

The above research agenda is relevant not only to the practical problems of responding to global change, but also to some basic issues in social science. The gaps in knowledge about international environmental regimes are also gaps in the broader literatures on social institutions and collective action. This global change research agenda would therefore be a direct and timely contribution to political science.

G LOBAL S OCIAL C HANGE

As we note at the opening of this chapter, the consequences of global environmental change depend on the future shape of human society. A number of ongoing changes in human systems, operating systemically or cumulatively at the global level, are shaping the societies that will feel the effects of global environmental change. Although global social changes are numerous, to our knowledge, a thoughtful typology of them has not been developed. As an impetus to further analysis and research, we note several examples of global social changes that may affect the driv-

ing or mitigating forces of global environmental change or the ability of human systems to respond to such change.

Population Distribution and Size The urban population of the world continues to increase both in total and in percentage terms, in both the developed and developing countries (Berry, 1991; Smith and London, 1990). Urbanization, by increasing spatial concentration, may increase vulnerability to natural hazards, concentrated pollutant emissions, and globally systemic changes such as sea-level rise. Urban bias in developing countries may also skew national priorities away from rural resource and environmental problems (Lipton, 1977). However, urbanization may decrease vulnerability by affording economies of scale in resource use and environmental protection, allowing rural households to diversify their sources of income, decreasing population growth rates, and increasing concern with environmental amenities. Some of the key research questions concern the conditions under which urbanization affects demand for resources implicated in global change, vulnerability to environmental disasters, and the robustness of rural communities in the face of environmental change. Equally relevant are concerns of population size. Increasing human population is likely to place added pressure on political and economic systems to contain conflicts likely to arise over increasingly scarce resources (see, e.g., Homer-Dixon, 1990).

Market Growth and Economic Development The spatial reach and dominance of market forces have been widening as a world system of trade penetrates even into countries that have had central planning and command economies and into the remotest regions. The effects on the human driving forces of global change and on the ability to respond are not obvious. Expansion of the market replaces state-sponsored resource waste with an invisible-hand means for checking inefficient and degrading uses of the environment. However, ceding control to the market can also lessen the ability of the state or community to manage environmental problems that are driven by the search for profits. At the local level, sustainable practices associated with a subsistence or mixed economy may be abandoned for unsustainable profit-oriented ones (Bates, 1980; Jodha and Mascarenhas, 1985; Redclift, 1987). The increased wealth that is the usual (though not always realized) goal of a shift toward free-market policies generally increases the ability to respond to threatening changes;

it may also raise the standard of environmental quality expected by the population.

Socioeconomic Marginalization Some observers hypothesize that the global spread of capitalism has forced certain individuals, groups, and countries into a position of diminishing control over needed resources and reduced options for survival and for responding to global change. Indigenous sociocultural systems of social security are believed to be crumbling, with new capitalist economies doing little to replace the lost safety nets. Economically marginalized individuals and groups sometimes degrade the environment for subsistence and lack the resources to respond effectively to natural or human-induced damage. Marginalization and impoverishment of nations can have the same consequences for national policies and actions (Hewitt, 1983; Sen, 1981; Watts, 1987).

Geopolitical Shifts The trend in 1989-1991 of declining tensions between East and West may facilitate human response to global environmental change through reallocating funds from military uses, lowering the potential for widespread nuclear and/ or chemical warfare, redefining national security to consider environmental as well as military and ideological threats (Brown, 1982; Mathews, 1989; Bush and Gorbachev, 1990), and building trust between powerful nations that will lead to cooperation instead of conflict. At the same time, however, north-south tensions may be increasing with the disparity of wealth between the developed and developing worlds. Such increased tension will make future international cooperative action more difficult and may lead to direct conflict (Agarwal, 1990; Carroll, 1983). The net effect of such geopolitical shifts is very hard to predict.

International Information/Communication Networks A global explosion of information and communication technology has uncertain implications for response to global change. It may facilitate societal response by making it easier for scientists and policy makers around the world to cooperate and share information, disseminate it to the public, and marshal worldwide pressure for response (Cleveland, 1990; Miles et al., 1988; Mowlana and Wilson, 1990; K. Wright, 1990). Examples include international reaction to satellite photographs of daily burning in the Amazon forests and the response of the Soviet peoples to news of the desiccation of the Aral Sea. However, the network may also amplify misinformation or create barriers to response by spreading the word that some nations may gain from environmental change.

Democratization As of mid-1991, there appears to be a worldwide trend toward increasing decision-making power of the

citizenry in nation-states. Increasing democratization may influence human response by providing more power to people being affected by environmental change, but it may also give more access and power to those whose interests would be harmed by measures for environmental management and protection. Democratization may also slow responses, compared with what might be achieved in an authoritarian regime by simple decision by the leadership (Kaplan, 1989; Muller, 1988; Roberts, 1990; Stephens, 1989). The net effects on response to global change are likely to depend on conditions in particular countries.

Scientific/Technological Expansion Exponential growth in scientific and technological knowledge both drives environmental change and increases the capacity to respond to it. It increases the ability to detect and understand threatening global environmental changes (e.g., the ozone hole) and provides alternatives to destructive products and practices (e.g., substitutes for CFCs) (AMBIO, 1989; Bacard, 1989; United Nations, 1989), but it may also create new global environmental problems (Kasprzyk, 1989; Russell, 1987). And new technologies may create major changes in the structure of human society, as in the case of CFC refrigeration technology or the periodic emergence of new energy sources to replace old ones as the basis of industry (Ausubel and Sladovich, 1989). In such instances, the implications for the global environment may remain uncertain for a long period.

Resurgence of Cultural Identity Many analysts perceive a worldwide resurgence of cultural identity or differentiation in recent decades: a deeply held attachment to groups (e.g., ethnic, religious, tribal, states) and the associated movements by these groups for autonomy of expression and decision (see Nash, 1989). Examples include the resurgence of ethnic nationalism in the Soviet Republics and the overt hostility, especially in Islamic countries, to the cultural invasion of Western values. The impact on response to global change is most likely to be felt when global changes or possible responses to them are perceived as threats to the values or livelihood of a particular group or when response requires cooperation between groups already in conflict.

The social changes mentioned appear to be ongoing trends, yet their future direction is, of course, uncertain. Equally uncertain are the effects of any trends in global human systems on the human ability to respond to global change. Plausible arguments can usually be made on both sides: a global social change may make resource use either more or less extensive and effective

human response either easier or harder to accomplish. The open questions point to many research opportunities for social scientists who have studied changes in these human systems and who would now consider their implications for human responses to global change.

CONCLUSIONS

This chapter examines the range of human consequences of global change and identifies specific areas in which new research can make important contributions to understanding. Where we identify research needs, priorities among studies should be set according to the criteria noted in Chapter 2 . We focus here on four general principles derived from this analysis that deserve special emphasis because they are fundamental, underappreciated, and point to critical directions for research.

T HE K NOWLEDGE B ASE FOR H UMAN R ESPONSES I S I NHERENTLY V ALUE L ADEN

We have identified the key link from environmental change to its human consequences as proximate effects on what humans value. Of course, what humans value depends on the humans. The wealthy tend to have different value priorities from the poor, national leaders from voters, business executives from laborers, miners from herders, and so forth. Yet what humans value is precisely what defines the consequences of global change and drives human responses. Different individuals and human groups will often disagree about what environmental changes are worthy of response.

Research Needs First, it is necessary to disaggregate the consequences of global change by analyzing the distribution of impacts of particular global changes on the things that different groups of people value. Such knowledge is necessary input to policy debates, even though it is not sufficient to facilitate social choices. Even with perfect knowledge of the effects of each conceivable alternative on each group affected, conflicts of value and interest will remain. Better knowledge of the impacts may even precipitate conflict by making latent conflicts more obvious.

Second, it is important to develop better ways of making the available knowledge about outcomes more accessible and understandable to nonspecialists. The body of knowledge about the de-

sign of messages about environmental risks and benefits can be brought to bear (National Research Council, 1989b; Mileti and Fitzpatrick, 1991). Better messages are also necessary but insufficient to facilitate social choices. They inform but do nothing to alter the differences in values and interests that produce conflict.

Third, it may help to understand the process of value judgment better. Several systematic methods have been used to assess the value people place on outcomes that may be affected by environmental change or responses to it, and to help individuals confront the value tradeoffs that policy choices often pose (e.g., Keeney and Raiffa, 1976; Mitchell and Carson, 1988). These methods of systematizing the valuation process can be applied to the valuation of the consequences of global change under different response regimes; such studies will advance understanding of valuation and may also help individuals and social groups choose their responses.

The most critical practical need is probably for effective means of managing the conflicts of value and interest that attend choices about global change. Human systems at every level of organization will have to develop systems of conflict management and, to the extent that different human groups (e.g., countries) need to respond in a coordinated way, their systems will also have to be compatible. These practical needs raise numerous research questions for the global change research agenda. In the discussion of conflict, we noted several bodies of relevant theory and knowledge that could be usefully applied to the study of conflict over responses to global environmental change. Methods of conflict management developed for other conflicts might be tried experimentally and monitored in efforts at global change-related conflict resolution. And experiments should be conducted with institutional means for making technological knowledge useful to nonexperts in a context of controversy—for instance, systems that enlist representatives of interested groups in the process (National Research Council, 1989b) or that harness the controversy to provide a range of perspectives as an aid to understanding (Stern, 1991).

H UMAN R ESPONSES M UST BE ASSESSED AGAINST A CHANGING BASELINE

The human consequences of an environmental change depend on when it happens and on the state of the affected human groups at that time. Global changes in the future may or may not have more serious effects than if they happened now. For instance, if recent trends continue, future societies will be wealthier, more

flexible, and more able to take global changes in stride than present ones. However, the more committed human societies become to present technologies that produce global change, the harder it will be to give them up if that becomes necessary.

Research Needs First, to understand the human consequences of global change, it is important to improve the ability to project social change. Existing methods range from simple extrapolation to more complex procedures for building scenarios. But scenario building is more art than science. Therefore, as an initial approach, it is useful to test projected environmental futures against various projected human futures to see how sensitive the human consequences of global change are to variations in the social future. In the longer run, it is much preferable to improve understanding of the relationships that drive social change. This is a long-term project in social science, on which much theoretical work is needed. We return to this theme in Chapter 5 . Research on the human dimensions of global change may help give impetus to that project.

Second, the extreme difficulty of predicting the long-term social future raises the importance of the study of social robustness in the face of environmental change. Increasing robustness against a range of environmental changes is a highly attractive strategy because it bypasses the difficult problems of predicting long-term environmental and social change. However, little is known about what makes social, economic, and technological systems robust, and the concept itself needs much more careful conceptualization.

The importance of the problem is suggested comparing two plausible arguments, both found in this chapter. One is that expansion of the market increases robustness by giving economic actors more flexibility in providing for their needs. This argument implies that further penetration of international markets will make it easier for humanity to withstand global changes without major suffering. The other argument is that sociocultural systems often provide a safety net for individuals, for example, through the obligations of others to provide. Sometimes, as in the responses to drought in northern Nigeria, these two arguments seem to support each other: the sociocultural systems there relied on the availability of urban wage labor as a supplement to subsistence agriculture. But sometimes, as with Amazonian deforestation, the two arguments seem to conflict: wealthy economic actors following market incentives crowd out peoples who have developed flexible sociocultural systems, leaving them neither land nor paid labor. Careful comparisons of cases such as the Sahel

and the Amazon might begin to clarify the role of markets and of various sociocultural systems in making social groups more or less robust with respect to environmental change.

H UMAN R ESPONSE C AN I NVOLVE I NTERVENTION A NYWHERE IN THE C YCLE OF C AUSATION

Human responses to global change can involve a variety of interventions of quite different types. It is reasonable to suppose that it makes a difference where an intervention occurs, but there is no body of knowledge that clarifies what different effects are likely to arise from different kinds of interventions. Consider an example in terms of Figure 4-1 . To respond to the threat of global warming, a government may regulate automobile manufacture or use (affecting a proximate cause—type P mitigation), institute a variety of fossil fuel taxes or incentives (to affect human systems that drive global change—type H mitigation), support research on solar energy (a more distantly type H mitigation), or support adjustment by investing in a fund to compensate citizens after the warming begins to affect what they value. Many arguments can be raised for each strategy. One may argue that mitigation directed at proximate causes is less likely to have disastrous side effects because it is targeted to the desired change only—or one may argue that adjustments are less likely to have disastrous side effects, for the same reason. One may argue that investing in solar energy is wiser than the other mitigation alternatives because it goes to the root of the carbon dioxide problem—or one may argue that it is less wise because too many things must go right for the investment to succeed. At present, not enough is known to shed light on such arguments in any systematic way.

We doubt that a general theory will be developed any time soon that can specify from the class of an intervention its likely effect and the types of unexpected consequences it might have. Such a theory will probably have to be inductive, and the necessary knowledge base does not exist. It is worthwhile to begin collecting the knowledge now.

Research Needs One research priority in the near-term should be to support studies that compare interventions at different points in the same causal cycle to identify their main and secondary effects. For example, the effects of regulating automobile fuel economy (a type P mitigation of global warming) can be compared with the effects of taxing gasoline (a type H mitigation); the ef-

fects of drought relief payments (an adjustment) can be compared with systems of crop insurance (an intervention to increase robustness). When the relevant interventions have been tried, the studies should be post hoc; when they have not been tried, theoretical analyses or studies based on responses to hypothetical situations will have to suffice.

Even absent a general theory of human intervention in environmental systems, the variety of opportunities to intervene implies an extensive agenda for ''normal'' social science research to assess the outcomes of interventions in response to anticipated or experienced environmental change. Research approaches developed for evaluating policy outcomes, studying the implementation process, comparing alternative approaches to regulation, and assessing the environmental and social impacts of government programs and policies can all be readily applied to the assessment of potential or actual responses to global change.

H UMAN R ESPONSES A FFECT THE D RIVING F ORCES OF G LOBAL C HANGE

Because the relationships of human systems and environmental systems are those of mutual causation, all human responses to global change potentially alter both systems. For many interventions, the secondary effects will be minuscule, but it is not always obvious which interventions will have the minuscule effects. Therefore, as a general rule, our conclusions about research on human causes apply equally to research on human responses. For example, policies in response to global change, which often attempt to change technology, social organization, economic structures, or even attitudes, contribute to the interactions of the human driving forces. Like the human causes, human responses can have short-term and long-term effects that may be quite different. And as with the study of the human causes, the study of human responses must be an interdisciplinary effort. Researchers will have to be attracted to the field from their home disciplines, and interdisciplinary research teams will have to be built. Human responses need to be studied separately at different levels of analysis and at different time scales; comparative studies in different social and temporal contexts are necessary; and research is needed to link responses at one level to those at other levels and short-term effects to long-term ones.

Global environmental change often seems to be the most carefully examined issue of our time. Yet understanding the human side—human causes of and responses to environmental change—has not yet received sustained attention. Global Environmental Change offers a strategy for combining the efforts of natural and social scientists to better understand how our actions influence global change and how global change influences us.

The volume is accessible to the nonscientist and provides a wide range of examples and case studies. It explores how the attitudes and actions of individuals, governments, and organizations intertwine to leave their mark on the health of the planet.

The book focuses on establishing a framework for this new field of study, identifying problems that must be overcome if we are to deepen our understanding of the human dimensions of global change, presenting conclusions and recommendations.

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Harris and Trump Offer a Clear Contrast on the Economy

Both candidates embrace expansions of government power to steer economic outcomes — but in vastly different areas.

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By Jim Tankersley

Jim Tankersley has covered economic policy in presidential elections since 2004.

Vice President Kamala Harris and former President Donald J. Trump flew to North Carolina this week to deliver what were billed as major speeches on the economy. Neither laid out a comprehensive policy plan — not Ms. Harris in her half-hour focus on housing, groceries and prescription drugs, nor Mr. Trump in 80 minutes of sprinkling various proposals among musings about dangerous immigrants.

But in their own ways, both candidates sent voters clear and important messages about their economic visions. Each embraced a vision of a powerful federal government, using its muscle to intervene in markets in pursuit of a stronger and more prosperous economy.

They just disagreed, almost entirely, on when and how that power should be used.

In Raleigh on Friday, Ms. Harris began to put her own stamp on the brand of progressive economics that has come to dominate Democratic politics over the last decade. That economic thinking embraces the idea that the federal government must act aggressively to foster competition and correct distortions in private markets.

The approach seeks large tax increases on corporations and high earners, to fund assistance for low-income and middle-class workers who are struggling to build wealth for themselves and their children. At the same time, it provides big tax breaks to companies engaged in what Ms. Harris and other progressives see as delivering great economic benefit — like manufacturing technologies needed to fight global warming , or building affordable housing.

That philosophy animated the policy agenda that Ms. Harris unveiled on Friday. She pledged to send up to $25,000 in down-payment assistance to every first-time home buyer over four years, while directing $40 billion to construction companies that build starter homes. She said she would permanently reinstate an expanded child tax credit that President Biden temporarily established with his 2021 stimulus law, while offering even more assistance to parents of newborns.

She called for a federal ban on corporate price gouging on groceries and for new federal enforcement tools to punish companies that unfairly push up food prices. “My plan will include new penalties for opportunistic companies that exploit crises and break the rules,” she said, adding: “We will help the food industry become more competitive, because I believe competition is the lifeblood of our economy.”

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