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A review of the global climate change impacts, adaptation, and sustainable mitigation measures

Kashif abbass.

1 School of Economics and Management, Nanjing University of Science and Technology, Nanjing, 210094 People’s Republic of China

Muhammad Zeeshan Qasim

2 Jiangsu Key Laboratory of Chemical Pollution Control and Resources Reuse, School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Xiaolingwei 200, Nanjing, 210094 People’s Republic of China

Huaming Song

Muntasir murshed.

3 School of Business and Economics, North South University, Dhaka, 1229 Bangladesh

4 Department of Journalism, Media and Communications, Daffodil International University, Dhaka, Bangladesh

Haider Mahmood

5 Department of Finance, College of Business Administration, Prince Sattam Bin Abdulaziz University, 173, Alkharj, 11942 Saudi Arabia

Ijaz Younis

Associated data.

Data sources and relevant links are provided in the paper to access data.

Climate change is a long-lasting change in the weather arrays across tropics to polls. It is a global threat that has embarked on to put stress on various sectors. This study is aimed to conceptually engineer how climate variability is deteriorating the sustainability of diverse sectors worldwide. Specifically, the agricultural sector’s vulnerability is a globally concerning scenario, as sufficient production and food supplies are threatened due to irreversible weather fluctuations. In turn, it is challenging the global feeding patterns, particularly in countries with agriculture as an integral part of their economy and total productivity. Climate change has also put the integrity and survival of many species at stake due to shifts in optimum temperature ranges, thereby accelerating biodiversity loss by progressively changing the ecosystem structures. Climate variations increase the likelihood of particular food and waterborne and vector-borne diseases, and a recent example is a coronavirus pandemic. Climate change also accelerates the enigma of antimicrobial resistance, another threat to human health due to the increasing incidence of resistant pathogenic infections. Besides, the global tourism industry is devastated as climate change impacts unfavorable tourism spots. The methodology investigates hypothetical scenarios of climate variability and attempts to describe the quality of evidence to facilitate readers’ careful, critical engagement. Secondary data is used to identify sustainability issues such as environmental, social, and economic viability. To better understand the problem, gathered the information in this report from various media outlets, research agencies, policy papers, newspapers, and other sources. This review is a sectorial assessment of climate change mitigation and adaptation approaches worldwide in the aforementioned sectors and the associated economic costs. According to the findings, government involvement is necessary for the country’s long-term development through strict accountability of resources and regulations implemented in the past to generate cutting-edge climate policy. Therefore, mitigating the impacts of climate change must be of the utmost importance, and hence, this global threat requires global commitment to address its dreadful implications to ensure global sustenance.

Introduction

Worldwide observed and anticipated climatic changes for the twenty-first century and global warming are significant global changes that have been encountered during the past 65 years. Climate change (CC) is an inter-governmental complex challenge globally with its influence over various components of the ecological, environmental, socio-political, and socio-economic disciplines (Adger et al.  2005 ; Leal Filho et al.  2021 ; Feliciano et al.  2022 ). Climate change involves heightened temperatures across numerous worlds (Battisti and Naylor  2009 ; Schuurmans  2021 ; Weisheimer and Palmer  2005 ; Yadav et al.  2015 ). With the onset of the industrial revolution, the problem of earth climate was amplified manifold (Leppänen et al.  2014 ). It is reported that the immediate attention and due steps might increase the probability of overcoming its devastating impacts. It is not plausible to interpret the exact consequences of climate change (CC) on a sectoral basis (Izaguirre et al.  2021 ; Jurgilevich et al.  2017 ), which is evident by the emerging level of recognition plus the inclusion of climatic uncertainties at both local and national level of policymaking (Ayers et al.  2014 ).

Climate change is characterized based on the comprehensive long-haul temperature and precipitation trends and other components such as pressure and humidity level in the surrounding environment. Besides, the irregular weather patterns, retreating of global ice sheets, and the corresponding elevated sea level rise are among the most renowned international and domestic effects of climate change (Lipczynska-Kochany  2018 ; Michel et al.  2021 ; Murshed and Dao 2020 ). Before the industrial revolution, natural sources, including volcanoes, forest fires, and seismic activities, were regarded as the distinct sources of greenhouse gases (GHGs) such as CO 2 , CH 4 , N 2 O, and H 2 O into the atmosphere (Murshed et al. 2020 ; Hussain et al.  2020 ; Sovacool et al.  2021 ; Usman and Balsalobre-Lorente 2022 ; Murshed 2022 ). United Nations Framework Convention on Climate Change (UNFCCC) struck a major agreement to tackle climate change and accelerate and intensify the actions and investments required for a sustainable low-carbon future at Conference of the Parties (COP-21) in Paris on December 12, 2015. The Paris Agreement expands on the Convention by bringing all nations together for the first time in a single cause to undertake ambitious measures to prevent climate change and adapt to its impacts, with increased funding to assist developing countries in doing so. As so, it marks a turning point in the global climate fight. The core goal of the Paris Agreement is to improve the global response to the threat of climate change by keeping the global temperature rise this century well below 2 °C over pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5° C (Sharma et al. 2020 ; Sharif et al. 2020 ; Chien et al. 2021 .

Furthermore, the agreement aspires to strengthen nations’ ability to deal with the effects of climate change and align financing flows with low GHG emissions and climate-resilient paths (Shahbaz et al. 2019 ; Anwar et al. 2021 ; Usman et al. 2022a ). To achieve these lofty goals, adequate financial resources must be mobilized and provided, as well as a new technology framework and expanded capacity building, allowing developing countries and the most vulnerable countries to act under their respective national objectives. The agreement also establishes a more transparent action and support mechanism. All Parties are required by the Paris Agreement to do their best through “nationally determined contributions” (NDCs) and to strengthen these efforts in the coming years (Balsalobre-Lorente et al. 2020 ). It includes obligations that all Parties regularly report on their emissions and implementation activities. A global stock-take will be conducted every five years to review collective progress toward the agreement’s goal and inform the Parties’ future individual actions. The Paris Agreement became available for signature on April 22, 2016, Earth Day, at the United Nations Headquarters in New York. On November 4, 2016, it went into effect 30 days after the so-called double threshold was met (ratification by 55 nations accounting for at least 55% of world emissions). More countries have ratified and continue to ratify the agreement since then, bringing 125 Parties in early 2017. To fully operationalize the Paris Agreement, a work program was initiated in Paris to define mechanisms, processes, and recommendations on a wide range of concerns (Murshed et al. 2021 ). Since 2016, Parties have collaborated in subsidiary bodies (APA, SBSTA, and SBI) and numerous formed entities. The Conference of the Parties functioning as the meeting of the Parties to the Paris Agreement (CMA) convened for the first time in November 2016 in Marrakesh in conjunction with COP22 and made its first two resolutions. The work plan is scheduled to be finished by 2018. Some mitigation and adaptation strategies to reduce the emission in the prospective of Paris agreement are following firstly, a long-term goal of keeping the increase in global average temperature to well below 2 °C above pre-industrial levels, secondly, to aim to limit the rise to 1.5 °C, since this would significantly reduce risks and the impacts of climate change, thirdly, on the need for global emissions to peak as soon as possible, recognizing that this will take longer for developing countries, lastly, to undertake rapid reductions after that under the best available science, to achieve a balance between emissions and removals in the second half of the century. On the other side, some adaptation strategies are; strengthening societies’ ability to deal with the effects of climate change and to continue & expand international assistance for developing nations’ adaptation.

However, anthropogenic activities are currently regarded as most accountable for CC (Murshed et al. 2022 ). Apart from the industrial revolution, other anthropogenic activities include excessive agricultural operations, which further involve the high use of fuel-based mechanization, burning of agricultural residues, burning fossil fuels, deforestation, national and domestic transportation sectors, etc. (Huang et al.  2016 ). Consequently, these anthropogenic activities lead to climatic catastrophes, damaging local and global infrastructure, human health, and total productivity. Energy consumption has mounted GHGs levels concerning warming temperatures as most of the energy production in developing countries comes from fossil fuels (Balsalobre-Lorente et al. 2022 ; Usman et al. 2022b ; Abbass et al. 2021a ; Ishikawa-Ishiwata and Furuya  2022 ).

This review aims to highlight the effects of climate change in a socio-scientific aspect by analyzing the existing literature on various sectorial pieces of evidence globally that influence the environment. Although this review provides a thorough examination of climate change and its severe affected sectors that pose a grave danger for global agriculture, biodiversity, health, economy, forestry, and tourism, and to purpose some practical prophylactic measures and mitigation strategies to be adapted as sound substitutes to survive from climate change (CC) impacts. The societal implications of irregular weather patterns and other effects of climate changes are discussed in detail. Some numerous sustainable mitigation measures and adaptation practices and techniques at the global level are discussed in this review with an in-depth focus on its economic, social, and environmental aspects. Methods of data collection section are included in the supplementary information.

Review methodology

Related study and its objectives.

Today, we live an ordinary life in the beautiful digital, globalized world where climate change has a decisive role. What happens in one country has a massive influence on geographically far apart countries, which points to the current crisis known as COVID-19 (Sarkar et al.  2021 ). The most dangerous disease like COVID-19 has affected the world’s climate changes and economic conditions (Abbass et al. 2022 ; Pirasteh-Anosheh et al.  2021 ). The purpose of the present study is to review the status of research on the subject, which is based on “Global Climate Change Impacts, adaptation, and sustainable mitigation measures” by systematically reviewing past published and unpublished research work. Furthermore, the current study seeks to comment on research on the same topic and suggest future research on the same topic. Specifically, the present study aims: The first one is, organize publications to make them easy and quick to find. Secondly, to explore issues in this area, propose an outline of research for future work. The third aim of the study is to synthesize the previous literature on climate change, various sectors, and their mitigation measurement. Lastly , classify the articles according to the different methods and procedures that have been adopted.

Review methodology for reviewers

This review-based article followed systematic literature review techniques that have proved the literature review as a rigorous framework (Benita  2021 ; Tranfield et al.  2003 ). Moreover, we illustrate in Fig.  1 the search method that we have started for this research. First, finalized the research theme to search literature (Cooper et al.  2018 ). Second, used numerous research databases to search related articles and download from the database (Web of Science, Google Scholar, Scopus Index Journals, Emerald, Elsevier Science Direct, Springer, and Sciverse). We focused on various articles, with research articles, feedback pieces, short notes, debates, and review articles published in scholarly journals. Reports used to search for multiple keywords such as “Climate Change,” “Mitigation and Adaptation,” “Department of Agriculture and Human Health,” “Department of Biodiversity and Forestry,” etc.; in summary, keyword list and full text have been made. Initially, the search for keywords yielded a large amount of literature.

Methodology search for finalized articles for investigations.

Source : constructed by authors

Since 2020, it has been impossible to review all the articles found; some restrictions have been set for the literature exhibition. The study searched 95 articles on a different database mentioned above based on the nature of the study. It excluded 40 irrelevant papers due to copied from a previous search after readings tiles, abstract and full pieces. The criteria for inclusion were: (i) articles focused on “Global Climate Change Impacts, adaptation, and sustainable mitigation measures,” and (ii) the search key terms related to study requirements. The complete procedure yielded 55 articles for our study. We repeat our search on the “Web of Science and Google Scholars” database to enhance the search results and check the referenced articles.

In this study, 55 articles are reviewed systematically and analyzed for research topics and other aspects, such as the methods, contexts, and theories used in these studies. Furthermore, this study analyzes closely related areas to provide unique research opportunities in the future. The study also discussed future direction opportunities and research questions by understanding the research findings climate changes and other affected sectors. The reviewed paper framework analysis process is outlined in Fig.  2 .

Framework of the analysis Process.

Natural disasters and climate change’s socio-economic consequences

Natural and environmental disasters can be highly variable from year to year; some years pass with very few deaths before a significant disaster event claims many lives (Symanski et al.  2021 ). Approximately 60,000 people globally died from natural disasters each year on average over the past decade (Ritchie and Roser  2014 ; Wiranata and Simbolon  2021 ). So, according to the report, around 0.1% of global deaths. Annual variability in the number and share of deaths from natural disasters in recent decades are shown in Fig.  3 . The number of fatalities can be meager—sometimes less than 10,000, and as few as 0.01% of all deaths. But shock events have a devastating impact: the 1983–1985 famine and drought in Ethiopia; the 2004 Indian Ocean earthquake and tsunami; Cyclone Nargis, which struck Myanmar in 2008; and the 2010 Port-au-Prince earthquake in Haiti and now recent example is COVID-19 pandemic (Erman et al.  2021 ). These events pushed global disaster deaths to over 200,000—more than 0.4% of deaths in these years. Low-frequency, high-impact events such as earthquakes and tsunamis are not preventable, but such high losses of human life are. Historical evidence shows that earlier disaster detection, more robust infrastructure, emergency preparedness, and response programmers have substantially reduced disaster deaths worldwide. Low-income is also the most vulnerable to disasters; improving living conditions, facilities, and response services in these areas would be critical in reducing natural disaster deaths in the coming decades.

Global deaths from natural disasters, 1978 to 2020.

Source EMDAT ( 2020 )

The interior regions of the continent are likely to be impacted by rising temperatures (Dimri et al.  2018 ; Goes et al.  2020 ; Mannig et al.  2018 ; Schuurmans  2021 ). Weather patterns change due to the shortage of natural resources (water), increase in glacier melting, and rising mercury are likely to cause extinction to many planted species (Gampe et al.  2016 ; Mihiretu et al.  2021 ; Shaffril et al.  2018 ).On the other hand, the coastal ecosystem is on the verge of devastation (Perera et al.  2018 ; Phillips  2018 ). The temperature rises, insect disease outbreaks, health-related problems, and seasonal and lifestyle changes are persistent, with a strong probability of these patterns continuing in the future (Abbass et al. 2021c ; Hussain et al.  2018 ). At the global level, a shortage of good infrastructure and insufficient adaptive capacity are hammering the most (IPCC  2013 ). In addition to the above concerns, a lack of environmental education and knowledge, outdated consumer behavior, a scarcity of incentives, a lack of legislation, and the government’s lack of commitment to climate change contribute to the general public’s concerns. By 2050, a 2 to 3% rise in mercury and a drastic shift in rainfall patterns may have serious consequences (Huang et al. 2022 ; Gorst et al.  2018 ). Natural and environmental calamities caused huge losses globally, such as decreased agriculture outputs, rehabilitation of the system, and rebuilding necessary technologies (Ali and Erenstein  2017 ; Ramankutty et al.  2018 ; Yu et al.  2021 ) (Table ​ (Table1). 1 ). Furthermore, in the last 3 or 4 years, the world has been plagued by smog-related eye and skin diseases, as well as a rise in road accidents due to poor visibility.

Main natural danger statistics for 1985–2020 at the global level

Source: EM-DAT ( 2020 )

Climate change and agriculture

Global agriculture is the ultimate sector responsible for 30–40% of all greenhouse emissions, which makes it a leading industry predominantly contributing to climate warming and significantly impacted by it (Grieg; Mishra et al.  2021 ; Ortiz et al.  2021 ; Thornton and Lipper  2014 ). Numerous agro-environmental and climatic factors that have a dominant influence on agriculture productivity (Pautasso et al.  2012 ) are significantly impacted in response to precipitation extremes including floods, forest fires, and droughts (Huang  2004 ). Besides, the immense dependency on exhaustible resources also fuels the fire and leads global agriculture to become prone to devastation. Godfray et al. ( 2010 ) mentioned that decline in agriculture challenges the farmer’s quality of life and thus a significant factor to poverty as the food and water supplies are critically impacted by CC (Ortiz et al.  2021 ; Rosenzweig et al.  2014 ). As an essential part of the economic systems, especially in developing countries, agricultural systems affect the overall economy and potentially the well-being of households (Schlenker and Roberts  2009 ). According to the report published by the Intergovernmental Panel on Climate Change (IPCC), atmospheric concentrations of greenhouse gases, i.e., CH 4, CO 2 , and N 2 O, are increased in the air to extraordinary levels over the last few centuries (Usman and Makhdum 2021 ; Stocker et al.  2013 ). Climate change is the composite outcome of two different factors. The first is the natural causes, and the second is the anthropogenic actions (Karami 2012 ). It is also forecasted that the world may experience a typical rise in temperature stretching from 1 to 3.7 °C at the end of this century (Pachauri et al. 2014 ). The world’s crop production is also highly vulnerable to these global temperature-changing trends as raised temperatures will pose severe negative impacts on crop growth (Reidsma et al. 2009 ). Some of the recent modeling about the fate of global agriculture is briefly described below.

Decline in cereal productivity

Crop productivity will also be affected dramatically in the next few decades due to variations in integral abiotic factors such as temperature, solar radiation, precipitation, and CO 2 . These all factors are included in various regulatory instruments like progress and growth, weather-tempted changes, pest invasions (Cammell and Knight 1992 ), accompanying disease snags (Fand et al. 2012 ), water supplies (Panda et al. 2003 ), high prices of agro-products in world’s agriculture industry, and preeminent quantity of fertilizer consumption. Lobell and field ( 2007 ) claimed that from 1962 to 2002, wheat crop output had condensed significantly due to rising temperatures. Therefore, during 1980–2011, the common wheat productivity trends endorsed extreme temperature events confirmed by Gourdji et al. ( 2013 ) around South Asia, South America, and Central Asia. Various other studies (Asseng, Cao, Zhang, and Ludwig 2009 ; Asseng et al. 2013 ; García et al. 2015 ; Ortiz et al. 2021 ) also proved that wheat output is negatively affected by the rising temperatures and also caused adverse effects on biomass productivity (Calderini et al. 1999 ; Sadras and Slafer 2012 ). Hereafter, the rice crop is also influenced by the high temperatures at night. These difficulties will worsen because the temperature will be rising further in the future owing to CC (Tebaldi et al. 2006 ). Another research conducted in China revealed that a 4.6% of rice production per 1 °C has happened connected with the advancement in night temperatures (Tao et al. 2006 ). Moreover, the average night temperature growth also affected rice indicia cultivar’s output pragmatically during 25 years in the Philippines (Peng et al. 2004 ). It is anticipated that the increase in world average temperature will also cause a substantial reduction in yield (Hatfield et al. 2011 ; Lobell and Gourdji 2012 ). In the southern hemisphere, Parry et al. ( 2007 ) noted a rise of 1–4 °C in average daily temperatures at the end of spring season unti the middle of summers, and this raised temperature reduced crop output by cutting down the time length for phenophases eventually reduce the yield (Hatfield and Prueger 2015 ; R. Ortiz 2008 ). Also, world climate models have recommended that humid and subtropical regions expect to be plentiful prey to the upcoming heat strokes (Battisti and Naylor 2009 ). Grain production is the amalgamation of two constituents: the average weight and the grain output/m 2 , however, in crop production. Crop output is mainly accredited to the grain quantity (Araus et al. 2008 ; Gambín and Borrás 2010 ). In the times of grain set, yield resources are mainly strewn between hitherto defined components, i.e., grain usual weight and grain output, which presents a trade-off between them (Gambín and Borrás 2010 ) beside disparities in per grain integration (B. L. Gambín et al. 2006 ). In addition to this, the maize crop is also susceptible to raised temperatures, principally in the flowering stage (Edreira and Otegui 2013 ). In reality, the lower grain number is associated with insufficient acclimatization due to intense photosynthesis and higher respiration and the high-temperature effect on the reproduction phenomena (Edreira and Otegui 2013 ). During the flowering phase, maize visible to heat (30–36 °C) seemed less anthesis-silking intermissions (Edreira et al. 2011 ). Another research by Dupuis and Dumas ( 1990 ) proved that a drop in spikelet when directly visible to high temperatures above 35 °C in vitro pollination. Abnormalities in kernel number claimed by Vega et al. ( 2001 ) is related to conceded plant development during a flowering phase that is linked with the active ear growth phase and categorized as a critical phase for approximation of kernel number during silking (Otegui and Bonhomme 1998 ).

The retort of rice output to high temperature presents disparities in flowering patterns, and seed set lessens and lessens grain weight (Qasim et al. 2020 ; Qasim, Hammad, Maqsood, Tariq, & Chawla). During the daytime, heat directly impacts flowers which lessens the thesis period and quickens the earlier peak flowering (Tao et al. 2006 ). Antagonistic effect of higher daytime temperature d on pollen sprouting proposed seed set decay, whereas, seed set was lengthily reduced than could be explicated by pollen growing at high temperatures 40◦C (Matsui et al. 2001 ).

The decline in wheat output is linked with higher temperatures, confirmed in numerous studies (Semenov 2009 ; Stone and Nicolas 1994 ). High temperatures fast-track the arrangements of plant expansion (Blum et al. 2001 ), diminution photosynthetic process (Salvucci and Crafts‐Brandner 2004 ), and also considerably affect the reproductive operations (Farooq et al. 2011 ).

The destructive impacts of CC induced weather extremes to deteriorate the integrity of crops (Chaudhary et al. 2011 ), e.g., Spartan cold and extreme fog cause falling and discoloration of betel leaves (Rosenzweig et al. 2001 ), giving them a somehow reddish appearance, squeezing of lemon leaves (Pautasso et al. 2012 ), as well as root rot of pineapple, have reported (Vedwan and Rhoades 2001 ). Henceforth, in tackling the disruptive effects of CC, several short-term and long-term management approaches are the crucial need of time (Fig.  4 ). Moreover, various studies (Chaudhary et al. 2011 ; Patz et al. 2005 ; Pautasso et al. 2012 ) have demonstrated adapting trends such as ameliorating crop diversity can yield better adaptability towards CC.

Schematic description of potential impacts of climate change on the agriculture sector and the appropriate mitigation and adaptation measures to overcome its impact.

Climate change impacts on biodiversity

Global biodiversity is among the severe victims of CC because it is the fastest emerging cause of species loss. Studies demonstrated that the massive scale species dynamics are considerably associated with diverse climatic events (Abraham and Chain 1988 ; Manes et al. 2021 ; A. M. D. Ortiz et al. 2021 ). Both the pace and magnitude of CC are altering the compatible habitat ranges for living entities of marine, freshwater, and terrestrial regions. Alterations in general climate regimes influence the integrity of ecosystems in numerous ways, such as variation in the relative abundance of species, range shifts, changes in activity timing, and microhabitat use (Bates et al. 2014 ). The geographic distribution of any species often depends upon its ability to tolerate environmental stresses, biological interactions, and dispersal constraints. Hence, instead of the CC, the local species must only accept, adapt, move, or face extinction (Berg et al. 2010 ). So, the best performer species have a better survival capacity for adjusting to new ecosystems or a decreased perseverance to survive where they are already situated (Bates et al. 2014 ). An important aspect here is the inadequate habitat connectivity and access to microclimates, also crucial in raising the exposure to climate warming and extreme heatwave episodes. For example, the carbon sequestration rates are undergoing fluctuations due to climate-driven expansion in the range of global mangroves (Cavanaugh et al. 2014 ).

Similarly, the loss of kelp-forest ecosystems in various regions and its occupancy by the seaweed turfs has set the track for elevated herbivory by the high influx of tropical fish populations. Not only this, the increased water temperatures have exacerbated the conditions far away from the physiological tolerance level of the kelp communities (Vergés et al. 2016 ; Wernberg et al. 2016 ). Another pertinent danger is the devastation of keystone species, which even has more pervasive effects on the entire communities in that habitat (Zarnetske et al. 2012 ). It is particularly important as CC does not specify specific populations or communities. Eventually, this CC-induced redistribution of species may deteriorate carbon storage and the net ecosystem productivity (Weed et al. 2013 ). Among the typical disruptions, the prominent ones include impacts on marine and terrestrial productivity, marine community assembly, and the extended invasion of toxic cyanobacteria bloom (Fossheim et al. 2015 ).

The CC-impacted species extinction is widely reported in the literature (Beesley et al. 2019 ; Urban 2015 ), and the predictions of demise until the twenty-first century are dreadful (Abbass et al. 2019 ; Pereira et al. 2013 ). In a few cases, northward shifting of species may not be formidable as it allows mountain-dwelling species to find optimum climates. However, the migrant species may be trapped in isolated and incompatible habitats due to losing topography and range (Dullinger et al. 2012 ). For example, a study indicated that the American pika has been extirpated or intensely diminished in some regions, primarily attributed to the CC-impacted extinction or at least local extirpation (Stewart et al. 2015 ). Besides, the anticipation of persistent responses to the impacts of CC often requires data records of several decades to rigorously analyze the critical pre and post CC patterns at species and ecosystem levels (Manes et al. 2021 ; Testa et al. 2018 ).

Nonetheless, the availability of such long-term data records is rare; hence, attempts are needed to focus on these profound aspects. Biodiversity is also vulnerable to the other associated impacts of CC, such as rising temperatures, droughts, and certain invasive pest species. For instance, a study revealed the changes in the composition of plankton communities attributed to rising temperatures. Henceforth, alterations in such aquatic producer communities, i.e., diatoms and calcareous plants, can ultimately lead to variation in the recycling of biological carbon. Moreover, such changes are characterized as a potential contributor to CO 2 differences between the Pleistocene glacial and interglacial periods (Kohfeld et al. 2005 ).

Climate change implications on human health

It is an understood corporality that human health is a significant victim of CC (Costello et al. 2009 ). According to the WHO, CC might be responsible for 250,000 additional deaths per year during 2030–2050 (Watts et al. 2015 ). These deaths are attributed to extreme weather-induced mortality and morbidity and the global expansion of vector-borne diseases (Lemery et al. 2021; Yang and Usman 2021 ; Meierrieks 2021 ; UNEP 2017 ). Here, some of the emerging health issues pertinent to this global problem are briefly described.

Climate change and antimicrobial resistance with corresponding economic costs

Antimicrobial resistance (AMR) is an up-surging complex global health challenge (Garner et al. 2019 ; Lemery et al. 2021 ). Health professionals across the globe are extremely worried due to this phenomenon that has critical potential to reverse almost all the progress that has been achieved so far in the health discipline (Gosling and Arnell 2016 ). A massive amount of antibiotics is produced by many pharmaceutical industries worldwide, and the pathogenic microorganisms are gradually developing resistance to them, which can be comprehended how strongly this aspect can shake the foundations of national and global economies (UNEP 2017 ). This statement is supported by the fact that AMR is not developing in a particular region or country. Instead, it is flourishing in every continent of the world (WHO 2018 ). This plague is heavily pushing humanity to the post-antibiotic era, in which currently antibiotic-susceptible pathogens will once again lead to certain endemics and pandemics after being resistant(WHO 2018 ). Undesirably, if this statement would become a factuality, there might emerge certain risks in undertaking sophisticated interventions such as chemotherapy, joint replacement cases, and organ transplantation (Su et al. 2018 ). Presently, the amplification of drug resistance cases has made common illnesses like pneumonia, post-surgical infections, HIV/AIDS, tuberculosis, malaria, etc., too difficult and costly to be treated or cure well (WHO 2018 ). From a simple example, it can be assumed how easily antibiotic-resistant strains can be transmitted from one person to another and ultimately travel across the boundaries (Berendonk et al. 2015 ). Talking about the second- and third-generation classes of antibiotics, e.g., most renowned generations of cephalosporin antibiotics that are more expensive, broad-spectrum, more toxic, and usually require more extended periods whenever prescribed to patients (Lemery et al. 2021 ; Pärnänen et al. 2019 ). This scenario has also revealed that the abundance of resistant strains of pathogens was also higher in the Southern part (WHO 2018 ). As southern parts are generally warmer than their counterparts, it is evident from this example how CC-induced global warming can augment the spread of antibiotic-resistant strains within the biosphere, eventually putting additional economic burden in the face of developing new and costlier antibiotics. The ARG exchange to susceptible bacteria through one of the potential mechanisms, transformation, transduction, and conjugation; Selection pressure can be caused by certain antibiotics, metals or pesticides, etc., as shown in Fig.  5 .

A typical interaction between the susceptible and resistant strains.

Source: Elsayed et al. ( 2021 ); Karkman et al. ( 2018 )

Certain studies highlighted that conventional urban wastewater treatment plants are typical hotspots where most bacterial strains exchange genetic material through horizontal gene transfer (Fig.  5 ). Although at present, the extent of risks associated with the antibiotic resistance found in wastewater is complicated; environmental scientists and engineers have particular concerns about the potential impacts of these antibiotic resistance genes on human health (Ashbolt 2015 ). At most undesirable and worst case, these antibiotic-resistant genes containing bacteria can make their way to enter into the environment (Pruden et al. 2013 ), irrigation water used for crops and public water supplies and ultimately become a part of food chains and food webs (Ma et al. 2019 ; D. Wu et al. 2019 ). This problem has been reported manifold in several countries (Hendriksen et al. 2019 ), where wastewater as a means of irrigated water is quite common.

Climate change and vector borne-diseases

Temperature is a fundamental factor for the sustenance of living entities regardless of an ecosystem. So, a specific living being, especially a pathogen, requires a sophisticated temperature range to exist on earth. The second essential component of CC is precipitation, which also impacts numerous infectious agents’ transport and dissemination patterns. Global rising temperature is a significant cause of many species extinction. On the one hand, this changing environmental temperature may be causing species extinction, and on the other, this warming temperature might favor the thriving of some new organisms. Here, it was evident that some pathogens may also upraise once non-evident or reported (Patz et al. 2000 ). This concept can be exemplified through certain pathogenic strains of microorganisms that how the likelihood of various diseases increases in response to climate warming-induced environmental changes (Table ​ (Table2 2 ).

Examples of how various environmental changes affect various infectious diseases in humans

Source: Aron and Patz ( 2001 )

A recent example is an outburst of coronavirus (COVID-19) in the Republic of China, causing pneumonia and severe acute respiratory complications (Cui et al. 2021 ; Song et al. 2021 ). The large family of viruses is harbored in numerous animals, bats, and snakes in particular (livescience.com) with the subsequent transfer into human beings. Hence, it is worth noting that the thriving of numerous vectors involved in spreading various diseases is influenced by Climate change (Ogden 2018 ; Santos et al. 2021 ).

Psychological impacts of climate change

Climate change (CC) is responsible for the rapid dissemination and exaggeration of certain epidemics and pandemics. In addition to the vast apparent impacts of climate change on health, forestry, agriculture, etc., it may also have psychological implications on vulnerable societies. It can be exemplified through the recent outburst of (COVID-19) in various countries around the world (Pal 2021 ). Besides, the victims of this viral infection have made healthy beings scarier and terrified. In the wake of such epidemics, people with common colds or fever are also frightened and must pass specific regulatory protocols. Living in such situations continuously terrifies the public and makes the stress familiar, which eventually makes them psychologically weak (npr.org).

CC boosts the extent of anxiety, distress, and other issues in public, pushing them to develop various mental-related problems. Besides, frequent exposure to extreme climatic catastrophes such as geological disasters also imprints post-traumatic disorder, and their ubiquitous occurrence paves the way to developing chronic psychological dysfunction. Moreover, repetitive listening from media also causes an increase in the person’s stress level (Association 2020 ). Similarly, communities living in flood-prone areas constantly live in extreme fear of drowning and die by floods. In addition to human lives, the flood-induced destruction of physical infrastructure is a specific reason for putting pressure on these communities (Ogden 2018 ). For instance, Ogden ( 2018 ) comprehensively denoted that Katrina’s Hurricane augmented the mental health issues in the victim communities.

Climate change impacts on the forestry sector

Forests are the global regulators of the world’s climate (FAO 2018 ) and have an indispensable role in regulating global carbon and nitrogen cycles (Rehman et al. 2021 ; Reichstein and Carvalhais 2019 ). Hence, disturbances in forest ecology affect the micro and macro-climates (Ellison et al. 2017 ). Climate warming, in return, has profound impacts on the growth and productivity of transboundary forests by influencing the temperature and precipitation patterns, etc. As CC induces specific changes in the typical structure and functions of ecosystems (Zhang et al. 2017 ) as well impacts forest health, climate change also has several devastating consequences such as forest fires, droughts, pest outbreaks (EPA 2018 ), and last but not the least is the livelihoods of forest-dependent communities. The rising frequency and intensity of another CC product, i.e., droughts, pose plenty of challenges to the well-being of global forests (Diffenbaugh et al. 2017 ), which is further projected to increase soon (Hartmann et al. 2018 ; Lehner et al. 2017 ; Rehman et al. 2021 ). Hence, CC induces storms, with more significant impacts also put extra pressure on the survival of the global forests (Martínez-Alvarado et al. 2018 ), significantly since their influences are augmented during higher winter precipitations with corresponding wetter soils causing weak root anchorage of trees (Brázdil et al. 2018 ). Surging temperature regimes causes alterations in usual precipitation patterns, which is a significant hurdle for the survival of temperate forests (Allen et al. 2010 ; Flannigan et al. 2013 ), letting them encounter severe stress and disturbances which adversely affects the local tree species (Hubbart et al. 2016 ; Millar and Stephenson 2015 ; Rehman et al. 2021 ).

Climate change impacts on forest-dependent communities

Forests are the fundamental livelihood resource for about 1.6 billion people worldwide; out of them, 350 million are distinguished with relatively higher reliance (Bank 2008 ). Agro-forestry-dependent communities comprise 1.2 billion, and 60 million indigenous people solely rely on forests and their products to sustain their lives (Sunderlin et al. 2005 ). For example, in the entire African continent, more than 2/3rd of inhabitants depend on forest resources and woodlands for their alimonies, e.g., food, fuelwood and grazing (Wasiq and Ahmad 2004 ). The livings of these people are more intensely affected by the climatic disruptions making their lives harder (Brown et al. 2014 ). On the one hand, forest communities are incredibly vulnerable to CC due to their livelihoods, cultural and spiritual ties as well as socio-ecological connections, and on the other, they are not familiar with the term “climate change.” (Rahman and Alam 2016 ). Among the destructive impacts of temperature and rainfall, disruption of the agroforestry crops with resultant downscale growth and yield (Macchi et al. 2008 ). Cruz ( 2015 ) ascribed that forest-dependent smallholder farmers in the Philippines face the enigma of delayed fruiting, more severe damages by insect and pest incidences due to unfavorable temperature regimes, and changed rainfall patterns.

Among these series of challenges to forest communities, their well-being is also distinctly vulnerable to CC. Though the detailed climate change impacts on human health have been comprehensively mentioned in the previous section, some studies have listed a few more devastating effects on the prosperity of forest-dependent communities. For instance, the Himalayan people have been experiencing frequent skin-borne diseases such as malaria and other skin diseases due to increasing mosquitoes, wild boar as well, and new wasps species, particularly in higher altitudes that were almost non-existent before last 5–10 years (Xu et al. 2008 ). Similarly, people living at high altitudes in Bangladesh have experienced frequent mosquito-borne calamities (Fardous; Sharma 2012 ). In addition, the pace of other waterborne diseases such as infectious diarrhea, cholera, pathogenic induced abdominal complications and dengue has also been boosted in other distinguished regions of Bangladesh (Cell 2009 ; Gunter et al. 2008 ).

Pest outbreak

Upscaling hotter climate may positively affect the mobile organisms with shorter generation times because they can scurry from harsh conditions than the immobile species (Fettig et al. 2013 ; Schoene and Bernier 2012 ) and are also relatively more capable of adapting to new environments (Jactel et al. 2019 ). It reveals that insects adapt quickly to global warming due to their mobility advantages. Due to past outbreaks, the trees (forests) are relatively more susceptible victims (Kurz et al. 2008 ). Before CC, the influence of factors mentioned earlier, i.e., droughts and storms, was existent and made the forests susceptible to insect pest interventions; however, the global forests remain steadfast, assiduous, and green (Jactel et al. 2019 ). The typical reasons could be the insect herbivores were regulated by several tree defenses and pressures of predation (Wilkinson and Sherratt 2016 ). As climate greatly influences these phenomena, the global forests cannot be so sedulous against such challenges (Jactel et al. 2019 ). Table ​ Table3 3 demonstrates some of the particular considerations with practical examples that are essential while mitigating the impacts of CC in the forestry sector.

Essential considerations while mitigating the climate change impacts on the forestry sector

Source : Fischer ( 2019 )

Climate change impacts on tourism

Tourism is a commercial activity that has roots in multi-dimensions and an efficient tool with adequate job generation potential, revenue creation, earning of spectacular foreign exchange, enhancement in cross-cultural promulgation and cooperation, a business tool for entrepreneurs and eventually for the country’s national development (Arshad et al. 2018 ; Scott 2021 ). Among a plethora of other disciplines, the tourism industry is also a distinct victim of climate warming (Gössling et al. 2012 ; Hall et al. 2015 ) as the climate is among the essential resources that enable tourism in particular regions as most preferred locations. Different places at different times of the year attract tourists both within and across the countries depending upon the feasibility and compatibility of particular weather patterns. Hence, the massive variations in these weather patterns resulting from CC will eventually lead to monumental challenges to the local economy in that specific area’s particular and national economy (Bujosa et al. 2015 ). For instance, the Intergovernmental Panel on Climate Change (IPCC) report demonstrated that the global tourism industry had faced a considerable decline in the duration of ski season, including the loss of some ski areas and the dramatic shifts in tourist destinations’ climate warming.

Furthermore, different studies (Neuvonen et al. 2015 ; Scott et al. 2004 ) indicated that various currently perfect tourist spots, e.g., coastal areas, splendid islands, and ski resorts, will suffer consequences of CC. It is also worth noting that the quality and potential of administrative management potential to cope with the influence of CC on the tourism industry is of crucial significance, which renders specific strengths of resiliency to numerous destinations to withstand against it (Füssel and Hildén 2014 ). Similarly, in the partial or complete absence of adequate socio-economic and socio-political capital, the high-demanding tourist sites scurry towards the verge of vulnerability. The susceptibility of tourism is based on different components such as the extent of exposure, sensitivity, life-supporting sectors, and capacity assessment factors (Füssel and Hildén 2014 ). It is obvious corporality that sectors such as health, food, ecosystems, human habitat, infrastructure, water availability, and the accessibility of a particular region are prone to CC. Henceforth, the sensitivity of these critical sectors to CC and, in return, the adaptive measures are a hallmark in determining the composite vulnerability of climate warming (Ionescu et al. 2009 ).

Moreover, the dependence on imported food items, poor hygienic conditions, and inadequate health professionals are dominant aspects affecting the local terrestrial and aquatic biodiversity. Meanwhile, the greater dependency on ecosystem services and its products also makes a destination more fragile to become a prey of CC (Rizvi et al. 2015 ). Some significant non-climatic factors are important indicators of a particular ecosystem’s typical health and functioning, e.g., resource richness and abundance portray the picture of ecosystem stability. Similarly, the species abundance is also a productive tool that ensures that the ecosystem has a higher buffering capacity, which is terrific in terms of resiliency (Roscher et al. 2013 ).

Climate change impacts on the economic sector

Climate plays a significant role in overall productivity and economic growth. Due to its increasingly global existence and its effect on economic growth, CC has become one of the major concerns of both local and international environmental policymakers (Ferreira et al. 2020 ; Gleditsch 2021 ; Abbass et al. 2021b ; Lamperti et al. 2021 ). The adverse effects of CC on the overall productivity factor of the agricultural sector are therefore significant for understanding the creation of local adaptation policies and the composition of productive climate policy contracts. Previous studies on CC in the world have already forecasted its effects on the agricultural sector. Researchers have found that global CC will impact the agricultural sector in different world regions. The study of the impacts of CC on various agrarian activities in other demographic areas and the development of relative strategies to respond to effects has become a focal point for researchers (Chandioet al. 2020 ; Gleditsch 2021 ; Mosavi et al. 2020 ).

With the rapid growth of global warming since the 1980s, the temperature has started increasing globally, which resulted in the incredible transformation of rain and evaporation in the countries. The agricultural development of many countries has been reliant, delicate, and susceptible to CC for a long time, and it is on the development of agriculture total factor productivity (ATFP) influence different crops and yields of farmers (Alhassan 2021 ; Wu  2020 ).

Food security and natural disasters are increasing rapidly in the world. Several major climatic/natural disasters have impacted local crop production in the countries concerned. The effects of these natural disasters have been poorly controlled by the development of the economies and populations and may affect human life as well. One example is China, which is among the world’s most affected countries, vulnerable to natural disasters due to its large population, harsh environmental conditions, rapid CC, low environmental stability, and disaster power. According to the January 2016 statistical survey, China experienced an economic loss of 298.3 billion Yuan, and about 137 million Chinese people were severely affected by various natural disasters (Xie et al. 2018 ).

Mitigation and adaptation strategies of climate changes

Adaptation and mitigation are the crucial factors to address the response to CC (Jahanzad et al. 2020 ). Researchers define mitigation on climate changes, and on the other hand, adaptation directly impacts climate changes like floods. To some extent, mitigation reduces or moderates greenhouse gas emission, and it becomes a critical issue both economically and environmentally (Botzen et al. 2021 ; Jahanzad et al. 2020 ; Kongsager 2018 ; Smit et al. 2000 ; Vale et al. 2021 ; Usman et al. 2021 ; Verheyen 2005 ).

Researchers have deep concern about the adaptation and mitigation methodologies in sectoral and geographical contexts. Agriculture, industry, forestry, transport, and land use are the main sectors to adapt and mitigate policies(Kärkkäinen et al. 2020 ; Waheed et al. 2021 ). Adaptation and mitigation require particular concern both at the national and international levels. The world has faced a significant problem of climate change in the last decades, and adaptation to these effects is compulsory for economic and social development. To adapt and mitigate against CC, one should develop policies and strategies at the international level (Hussain et al. 2020 ). Figure  6 depicts the list of current studies on sectoral impacts of CC with adaptation and mitigation measures globally.

Sectoral impacts of climate change with adaptation and mitigation measures.

Conclusion and future perspectives

Specific socio-agricultural, socio-economic, and physical systems are the cornerstone of psychological well-being, and the alteration in these systems by CC will have disastrous impacts. Climate variability, alongside other anthropogenic and natural stressors, influences human and environmental health sustainability. Food security is another concerning scenario that may lead to compromised food quality, higher food prices, and inadequate food distribution systems. Global forests are challenged by different climatic factors such as storms, droughts, flash floods, and intense precipitation. On the other hand, their anthropogenic wiping is aggrandizing their existence. Undoubtedly, the vulnerability scale of the world’s regions differs; however, appropriate mitigation and adaptation measures can aid the decision-making bodies in developing effective policies to tackle its impacts. Presently, modern life on earth has tailored to consistent climatic patterns, and accordingly, adapting to such considerable variations is of paramount importance. Because the faster changes in climate will make it harder to survive and adjust, this globally-raising enigma calls for immediate attention at every scale ranging from elementary community level to international level. Still, much effort, research, and dedication are required, which is the most critical time. Some policy implications can help us to mitigate the consequences of climate change, especially the most affected sectors like the agriculture sector;

Warming might lengthen the season in frost-prone growing regions (temperate and arctic zones), allowing for longer-maturing seasonal cultivars with better yields (Pfadenhauer 2020 ; Bonacci 2019 ). Extending the planting season may allow additional crops each year; when warming leads to frequent warmer months highs over critical thresholds, a split season with a brief summer fallow may be conceivable for short-period crops such as wheat barley, cereals, and many other vegetable crops. The capacity to prolong the planting season in tropical and subtropical places where the harvest season is constrained by precipitation or agriculture farming occurs after the year may be more limited and dependent on how precipitation patterns vary (Wu et al. 2017 ).

The genetic component is comprehensive for many yields, but it is restricted like kiwi fruit for a few. Ali et al. ( 2017 ) investigated how new crops will react to climatic changes (also stated in Mall et al. 2017 ). Hot temperature, drought, insect resistance; salt tolerance; and overall crop production and product quality increases would all be advantageous (Akkari 2016 ). Genetic mapping and engineering can introduce a greater spectrum of features. The adoption of genetically altered cultivars has been slowed, particularly in the early forecasts owing to the complexity in ensuring features are expediently expressed throughout the entire plant, customer concerns, economic profitability, and regulatory impediments (Wirehn 2018 ; Davidson et al. 2016 ).

To get the full benefit of the CO 2 would certainly require additional nitrogen and other fertilizers. Nitrogen not consumed by the plants may be excreted into groundwater, discharged into water surface, or emitted from the land, soil nitrous oxide when large doses of fertilizer are sprayed. Increased nitrogen levels in groundwater sources have been related to human chronic illnesses and impact marine ecosystems. Cultivation, grain drying, and other field activities have all been examined in depth in the studies (Barua et al. 2018 ).

• The technological and socio-economic adaptation

The policy consequence of the causative conclusion is that as a source of alternative energy, biofuel production is one of the routes that explain oil price volatility separate from international macroeconomic factors. Even though biofuel production has just begun in a few sample nations, there is still a tremendous worldwide need for feedstock to satisfy industrial expansion in China and the USA, which explains the food price relationship to the global oil price. Essentially, oil-exporting countries may create incentives in their economies to increase food production. It may accomplish by giving farmers financing, seedlings, fertilizers, and farming equipment. Because of the declining global oil price and, as a result, their earnings from oil export, oil-producing nations may be unable to subsidize food imports even in the near term. As a result, these countries can boost the agricultural value chain for export. It may be accomplished through R&D and adding value to their food products to increase income by correcting exchange rate misalignment and adverse trade terms. These nations may also diversify their economies away from oil, as dependence on oil exports alone is no longer economically viable given the extreme volatility of global oil prices. Finally, resource-rich and oil-exporting countries can convert to non-food renewable energy sources such as solar, hydro, coal, wind, wave, and tidal energy. By doing so, both world food and oil supplies would be maintained rather than harmed.

IRENA’s modeling work shows that, if a comprehensive policy framework is in place, efforts toward decarbonizing the energy future will benefit economic activity, jobs (outweighing losses in the fossil fuel industry), and welfare. Countries with weak domestic supply chains and a large reliance on fossil fuel income, in particular, must undertake structural reforms to capitalize on the opportunities inherent in the energy transition. Governments continue to give major policy assistance to extract fossil fuels, including tax incentives, financing, direct infrastructure expenditures, exemptions from environmental regulations, and other measures. The majority of major oil and gas producing countries intend to increase output. Some countries intend to cut coal output, while others plan to maintain or expand it. While some nations are beginning to explore and execute policies aimed at a just and equitable transition away from fossil fuel production, these efforts have yet to impact major producing countries’ plans and goals. Verifiable and comparable data on fossil fuel output and assistance from governments and industries are critical to closing the production gap. Governments could increase openness by declaring their production intentions in their climate obligations under the Paris Agreement.

It is firmly believed that achieving the Paris Agreement commitments is doubtlful without undergoing renewable energy transition across the globe (Murshed 2020 ; Zhao et al. 2022 ). Policy instruments play the most important role in determining the degree of investment in renewable energy technology. This study examines the efficacy of various policy strategies in the renewable energy industry of multiple nations. Although its impact is more visible in established renewable energy markets, a renewable portfolio standard is also a useful policy instrument. The cost of producing renewable energy is still greater than other traditional energy sources. Furthermore, government incentives in the R&D sector can foster innovation in this field, resulting in cost reductions in the renewable energy industry. These nations may export their technologies and share their policy experiences by forming networks among their renewable energy-focused organizations. All policy measures aim to reduce production costs while increasing the proportion of renewables to a country’s energy system. Meanwhile, long-term contracts with renewable energy providers, government commitment and control, and the establishment of long-term goals can assist developing nations in deploying renewable energy technology in their energy sector.

Author contribution

KA: Writing the original manuscript, data collection, data analysis, Study design, Formal analysis, Visualization, Revised draft, Writing-review, and editing. MZQ: Writing the original manuscript, data collection, data analysis, Writing-review, and editing. HS: Contribution to the contextualization of the theme, Conceptualization, Validation, Supervision, literature review, Revised drapt, and writing review and editing. MM: Writing review and editing, compiling the literature review, language editing. HM: Writing review and editing, compiling the literature review, language editing. IY: Contribution to the contextualization of the theme, literature review, and writing review and editing.

Availability of data and material

Declarations.

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The authors declare no competing interests.

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Contributor Information

Kashif Abbass, Email: nc.ude.tsujn@ssabbafihsak .

Muhammad Zeeshan Qasim, Email: moc.kooltuo@888misaqnahseez .

Huaming Song, Email: nc.ude.tsujn@gnimauh .

Muntasir Murshed, Email: [email protected] .

Haider Mahmood, Email: moc.liamtoh@doomhamrediah .

Ijaz Younis, Email: nc.ude.tsujn@sinuoyzaji .

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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 .

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Global warming is the long-term warming of the planet’s overall temperature. Though this warming trend has been going on for a long time, its pace has significantly increased in the last hundred years due to the burning of fossil fuels . As the human population has increased, so has the volume of fossil fuels burned. Fossil fuels include coal, oil, and natural gas, and burning them causes what is known as the “greenhouse effect” in Earth’s atmosphere.

The greenhouse effect is when the sun’s rays penetrate the atmosphere, but when that heat is reflected off the surface cannot escape back into space. Gases produced by the burning of fossil fuels prevent the heat from leaving the atmosphere. These greenhouse gasses are carbon dioxide , chlorofluorocarbons, water vapor , methane , and nitrous oxide . The excess heat in the atmosphere has caused the average global temperature to rise overtime, otherwise known as global warming.

Global warming has presented another issue called climate change. Sometimes these phrases are used interchangeably, however, they are different. Climate change refers to changes in weather patterns and growing seasons around the world. It also refers to sea level rise caused by the expansion of warmer seas and melting ice sheets and glaciers . Global warming causes climate change, which poses a serious threat to life on Earth in the forms of widespread flooding and extreme weather. Scientists continue to study global warming and its impact on Earth.

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Researchers who helped shape our understanding of climate change win Nobel Prize

Geoff Brumfiel

The Nobel Prize in physics went to three scientists this year for their work on climate change and chaotic systems.

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What evidence exists that Earth is warming and that humans are the main cause?

We know the world is warming because people have been recording daily high and low temperatures at thousands of weather stations worldwide, over land and ocean, for many decades and, in some locations, for more than a century. When different teams of climate scientists in different agencies (e.g., NOAA and NASA) and in other countries (e.g., the U.K.’s Hadley Centre) average these data together, they all find essentially the same result: Earth’s average surface temperature has risen by about 1.8°F (1.0°C) since 1880. 

( bar chart ) Yearly temperature compared to the twentieth-century average from 1850–2023. Red bars mean warmer-than-average years; blue bars mean colder-than-average years. (line graph) Atmospheric carbon dioxide amounts: 1850-1958 from IAC , 1959-2023 from NOAA Global Monitoring Lab . NOAA Climate.gov graph, adapted from original by Dr. Howard Diamond (NOAA ARL).

In addition to our surface station data, we have many different lines of evidence that Earth is warming ( learn more ). Birds are migrating earlier, and their migration patterns are changing.  Lobsters  and  other marine species  are moving north. Plants are blooming earlier in the spring. Mountain glaciers are melting worldwide, and snow cover is declining in the Northern Hemisphere (Learn more  here  and  here ). Greenland’s ice sheet—which holds about 8 percent of Earth’s fresh water—is melting at an accelerating rate ( learn more ). Mean global sea level is rising ( learn more ). Arctic sea ice is declining rapidly in both thickness and extent ( learn more ).

The Greenland Ice Sheet lost mass again in 2020, but not as much as it did 2019. Adapted from the 2020 Arctic Report Card, this graph tracks Greenland mass loss measured by NASA's GRACE satellite missions since 2002. The background photo shows a glacier calving front in western Greenland, captured from an airplane during a NASA Operation IceBridge field campaign. Full story.

We know this warming is largely caused by human activities because the key role that carbon dioxide plays in maintaining Earth’s natural greenhouse effect has been understood since the mid-1800s. Unless it is offset by some equally large cooling influence, more atmospheric carbon dioxide will lead to warmer surface temperatures. Since 1800, the amount of carbon dioxide in the atmosphere  has increased  from about 280 parts per million to 410 ppm in 2019. We know from both its rapid increase and its isotopic “fingerprint” that the source of this new carbon dioxide is fossil fuels, and not natural sources like forest fires, volcanoes, or outgassing from the ocean.

Philip James de Loutherbourg's 1801 painting, Coalbrookdale by Night , came to symbolize the start of the Industrial Revolution, when humans began to harness the power of fossil fuels—and to contribute significantly to Earth's atmospheric greenhouse gas composition. Image from Wikipedia .

Finally, no other known climate influences have changed enough to account for the observed warming trend. Taken together, these and other lines of evidence point squarely to human activities as the cause of recent global warming.

USGCRP (2017). Climate Science Special Report: Fourth National Climate Assessment, Volume 1 [Wuebbles, D.J., D.W. Fahey, K.A. Hibbard, D.J. Dokken, B.C. Stewart, and T.K. Maycock (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 470 pp, doi:  10.7930/J0J964J6 .

National Fish, Wildlife, and Plants Climate Adaptation Partnership (2012):  National Fish, Wildlife, and Plants Climate Adaptation Strategy . Association of Fish and Wildlife Agencies, Council on Environmental Quality, Great Lakes Indian Fish and Wildlife Commission, National Oceanic and Atmospheric Administration, and U.S. Fish and Wildlife Service. Washington, D.C. DOI: 10.3996/082012-FWSReport-1

IPCC (2019). Summary for Policymakers. In: IPCC Special Report on the Ocean and Cryosphere in a Changing Climate. [H.-O. Pörtner, D.C. Roberts, V. Masson-Delmotte, P. Zhai, M. Tignor, E. Poloczanska, K. Mintenbeck, A. Alegría, M. Nicolai, A. Okem, J. Petzold, B. Rama, N.M. Weyer (eds.)]. In press.

NASA JPL: "Consensus: 97% of climate scientists agree."  Global Climate Change . A website at NASA's Jet Propulsion Laboratory (climate.nasa.gov/scientific-consensus). (Accessed July 2013.)

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Climate change: a threat to human wellbeing and health of the planet. taking action now can secure our future.

BERLIN, Feb 28 – Human-induced climate change is causing dangerous and widespread disruption in nature and affecting the lives of billions of people around the world, despite efforts to reduce the risks. People and ecosystems least able to cope are being hardest hit, said scientists in the latest Intergovernmental Panel on Climate Change (IPCC) report, released today.

“This report is a dire warning about the consequences of inaction,” said Hoesung Lee, Chair of the IPCC. “It shows that climate change is a grave and mounting threat to our wellbeing and a healthy planet. Our actions today will shape how people adapt and nature responds to increasing climate risks.”

The world faces unavoidable multiple climate hazards over the next two decades with global warming of 1.5°C (2.7°F). Even temporarily exceeding this warming level will result in additional severe impacts, some of which will be irreversible. Risks for society will increase, including to infrastructure and low-lying coastal settlements.

The Summary for Policymakers of the IPCC Working Group II report,  Climate Change 2022: Impacts, Adaptation and Vulnerability was approved on Sunday, February 27 2022, by 195 member governments of the IPCC, through a virtual approval session that was held over two weeks starting on February 14.

Urgent action required to deal with increasing risks

Increased heatwaves, droughts and floods are already exceeding plants’ and animals’ tolerance thresholds, driving mass mortalities in species such as trees and corals. These weather extremes are occurring simultaneously, causing cascading impacts that are increasingly difficult to manage. They have exposed millions of people to acute food and water insecurity, especially in Africa, Asia, Central and South America, on Small Islands and in the Arctic.

To avoid mounting loss of life, biodiversity and infrastructure, ambitious, accelerated action is required to adapt to climate change, at the same time as making rapid, deep cuts in greenhouse gas emissions. So far, progress on adaptation is uneven and there are increasing gaps between action taken and what is needed to deal with the increasing risks, the new report finds. These gaps are largest among lower-income populations. 

The Working Group II report is the second instalment of the IPCC’s Sixth Assessment Report (AR6), which will be completed this year.

“This report recognizes the interdependence of climate, biodiversity and people and integrates natural, social and economic sciences more strongly than earlier IPCC assessments,” said Hoesung Lee. “It emphasizes the urgency of immediate and more ambitious action to address climate risks. Half measures are no longer an option.”

Safeguarding and strengthening nature is key to securing a liveable future

There are options to adapt to a changing climate. This report provides new insights into nature’s potential not only to reduce climate risks but also to improve people’s lives.

“Healthy ecosystems are more resilient to climate change and provide life-critical services such as food and clean water”, said IPCC Working Group II Co-Chair Hans-Otto Pörtner. “By restoring degraded ecosystems and effectively and equitably conserving 30 to 50 per cent of Earth’s land, freshwater and ocean habitats, society can benefit from nature’s capacity to absorb and store carbon, and we can accelerate progress towards sustainable development, but adequate finance and political support are essential.”

Scientists point out that climate change interacts with global trends such as unsustainable use of natural resources, growing urbanization, social inequalities, losses and damages from extreme events and a pandemic, jeopardizing future development.

“Our assessment clearly shows that tackling all these different challenges involves everyone – governments, the private sector, civil society – working together to prioritize risk reduction, as well as equity and justice, in decision-making and investment,” said IPCC Working Group II Co-Chair Debra Roberts.

“In this way, different interests, values and world views can be reconciled. By bringing together scientific and technological know-how as well as Indigenous and local knowledge, solutions will be more effective. Failure to achieve climate resilient and sustainable development will result in a sub-optimal future for people and nature.”

Cities: Hotspots of impacts and risks, but also a crucial part of the solution

This report provides a detailed assessment of climate change impacts, risks and adaptation in cities, where more than half the world’s population lives. People’s health, lives and livelihoods, as well as property and critical infrastructure, including energy and transportation systems, are being increasingly adversely affected by hazards from heatwaves, storms, drought and flooding as well as slow-onset changes, including sea level rise.

“Together, growing urbanization and climate change create complex risks, especially for those cities that already experience poorly planned urban growth, high levels of poverty and unemployment, and a lack of basic services,” Debra Roberts said.

“But cities also provide opportunities for climate action – green buildings, reliable supplies of clean water and renewable energy, and sustainable transport systems that connect urban and rural areas can all lead to a more inclusive, fairer society.”

There is increasing evidence of adaptation that has caused unintended consequences, for example destroying nature, putting peoples’ lives at risk or increasing greenhouse gas emissions. This can be avoided by involving everyone in planning, attention to equity and justice, and drawing on Indigenous and local knowledge.

A narrowing window for action

Climate change is a global challenge that requires local solutions and that’s why the Working Group II contribution to the IPCC’s Sixth Assessment Report (AR6) provides extensive regional information to enable Climate Resilient Development.

The report clearly states Climate Resilient Development is already challenging at current warming levels. It will become more limited if global warming exceeds 1.5°C (2.7°F). In some regions it will be impossible if global warming exceeds 2°C (3.6°F). This key finding underlines the urgency for climate action, focusing on equity and justice. Adequate funding, technology transfer, political commitment and partnership lead to more effective climate change adaptation and emissions reductions.

“The scientific evidence is unequivocal: climate change is a threat to human wellbeing and the health of the planet. Any further delay in concerted global action will miss a brief and rapidly closing window to secure a liveable future,” said Hans-Otto Pörtner.

For more information, please contact:

IPCC Press Office, Email: [email protected]   IPCC Working Group II:  Sina Löschke,  Komila Nabiyeva: [email protected]

Notes for Editors

Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change

The Working Group II report examines the impacts of climate change on nature and people around the globe. It explores future impacts at different levels of warming and the resulting risks and offers options to strengthen nature’s and society’s resilience to ongoing climate change, to fight hunger, poverty, and inequality and keep Earth a place worth living on – for current as well as for future generations. 

Working Group II introduces several new components in its latest report: One is a special section on climate change impacts, risks and options to act for cities and settlements by the sea, tropical forests, mountains, biodiversity hotspots, dryland and deserts, the Mediterranean as well as the polar regions. Another is an atlas that will present data and findings on observed and projected climate change impacts and risks from global to regional scales, thus offering even more insights for decision makers.

The Summary for Policymakers of the Working Group II contribution to the Sixth Assessment Report (AR6) as well as additional materials and information are available at https://www.ipcc.ch/report/ar6/wg2/

Note : Originally scheduled for release in September 2021, the report was delayed for several months by the COVID-19 pandemic, as work in the scientific community including the IPCC shifted online. This is the second time that the IPCC has conducted a virtual approval session for one of its reports.

AR6 Working Group II in numbers

270 authors from 67 countries

• 47 – coordinating authors
• 184 – lead authors
• 39 – review editors
• 675 – contributing authors

Over 34,000 cited references

A total of 62,418 expert and government review comments

(First Order Draft 16,348; Second Order Draft 40,293; Final Government Distribution: 5,777)

More information about the Sixth Assessment Report can be found  here .

Additional media resources

Assets available after the embargo is lifted on Media Essentials website .

Press conference recording, collection of sound bites from WGII authors, link to presentation slides, B-roll of approval session, link to launch Trello board including press release and video trailer in UN languages, a social media pack.

The website includes  outreach materials  such as videos about the IPCC and video recordings from  outreach events  conducted as webinars or live-streamed events.

Most videos published by the IPCC can be found on our  YouTube  channel. Credit for artwork

About the IPCC

The Intergovernmental Panel on Climate Change (IPCC) is the UN body for assessing the science related to climate change. It was established by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) in 1988 to provide political leaders with periodic scientific assessments concerning climate change, its implications and risks, as well as to put forward adaptation and mitigation strategies. In the same year the UN General Assembly endorsed the action by the WMO and UNEP in jointly establishing the IPCC. It has 195 member states.

Thousands of people from all over the world contribute to the work of the IPCC. For the assessment reports, IPCC scientists volunteer their time to assess the thousands of scientific papers published each year to provide a comprehensive summary of what is known about the drivers of climate change, its impacts and future risks, and how adaptation and mitigation can reduce those risks.

The IPCC has three working groups:  Working Group I , dealing with the physical science basis of climate change;  Working Group II , dealing with impacts, adaptation and vulnerability; and  Working Group III , dealing with the mitigation of climate change. It also has a  Task Force on National Greenhouse Gas Inventories  that develops methodologies for measuring emissions and removals. As part of the IPCC, a Task Group on Data Support for Climate Change Assessments (TG-Data) provides guidance to the Data Distribution Centre (DDC) on curation, traceability, stability, availability and transparency of data and scenarios related to the reports of the IPCC.

IPCC assessments provide governments, at all levels, with scientific information that they can use to develop climate policies. IPCC assessments are a key input into the international negotiations to tackle climate change. IPCC reports are drafted and reviewed in several stages, thus guaranteeing objectivity and transparency. An IPCC assessment report consists of the contributions of the three working groups and a Synthesis Report. The Synthesis Report integrates the findings of the three working group reports and of any special reports prepared in that assessment cycle.

About the Sixth Assessment Cycle

At its 41st Session in February 2015, the IPCC decided to produce a Sixth Assessment Report (AR6). At its 42nd Session in October 2015 it elected a new Bureau that would oversee the work on this report and the Special Reports to be produced in the assessment cycle.

Global Warming of 1.5°C , an IPCC special report on the impacts of global warming of 1.5 degrees Celsius above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty  was launched in October 2018.

Climate Change and Land , an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems  was launched in August 2019, and the  Special Report on the Ocean and Cryosphere in a Changing Climate  was released in September 2019.

In May 2019 the IPCC released the  2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories , an update to the methodology used by governments to estimate their greenhouse gas emissions and removals.

In August 2021 the IPCC released the Working Group I contribution to the AR6, Climate Change 2021, the Physical Science Basis

The Working Group III contribution to the AR6 is scheduled for early April 2022.

The Synthesis Report of the Sixth Assessment Report will be completed in the second half of 2022.

For more information go to  www.ipcc.ch

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Remarks by the ipcc chair during the press conference to present the working group ii contribution to the sixth assessment report.

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Fifty-fifth session of the ipcc (ipcc-55) and twelfth session of working group ii (wgii-12), february 14, 2022, working group report, ar6 climate change 2022: impacts, adaptation and vulnerability.

Global Warming

Long-term warming trends and increases in extreme weather events have the potential to impact all life on Earth. Even though at least 97 percent of climate scientists agree that human activities have contributed to rising global temperatures, the predominance and causes of these phenomena continue to be debated and many Americans deny global warming.

Read the overview below to gain a balanced understanding of the issues and explore the previews of opinion articles that highlight many perspectives on the response to global warming and climate change.

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Global warming topic overview.

"Global Warming and Climate Change." Opposing Viewpoints Online Collection , Gale, 2023.

Though the terms global warming and climate change are often used interchangeably, they have different meanings. Climate change describes long-term shifts in Earth's weather patterns that affect temperature, humidity, wind, cloud cover, and precipitation. Global warming refers explicitly to an increase in Earth's average surface temperatures caused by human activities, primarily the burning of fossil fuels. Anthropogenic climate change refers to changes in the climate caused by human activity, particularly industrialization and agricultural practices that release pollutants into the atmosphere.

Overwhelming scientific evidence supports the existence of both global warming and climate change. Through the United Nations' (UN) Intergovernmental Panel on Climate Change (IPCC), thousands of scientists work together to collect and analyze the latest available research related to climate change, its effects, and potential responses. In an interim update to its Sixth Assessment Report (AR6) in 2023, the IPCC estimated that global surface temperatures increased by 1.1°C (1.98°F) between the latter half of the nineteenth century and the first two decades of the twenty-first century. The IPCC has linked climate change and global warming to the increased occurrence and severity of storms, floods, droughts, and wildfires, warning that such disasters will increase further if temperatures continue to rise. The scientists' group also identifies water availability and food production as well as health and wealth being as experiencing observable, widespread, and substantial changes related to climate change. These threats have led scientists to identify global warming and climate change as a climate crisis . The IPCC recognizes human activity, particularly industrialization and certain agricultural practices that release carbon dioxide (CO2), as the primary driver of global warming and climate change.

Despite substantial evidence and a consensus among the scientific community, a vocal minority continues to challenge the science behind climate change. These critics characterize climate change as a natural phenomenon and dispute assertions that human activity has contributed to rising global temperatures. This position may be referred to as climate denial , and those who reject the scientific consensus are considered climate deniers . Fossil fuel companies often provide financial support to politicians, media campaigns, and organizations that promote climate denial.

• Climate chang e refers to long-term shifts in weather patterns. Global warming is the increase in the planet's average surface temperatures caused by human activities such as the burning of fossil fuels.
• Causes of climate change related to human activity are referred to as anthropogenic . Natural causes of climate change are called naturogenic .
• Earth's atmosphere contains several gases that trap heat from the sun and prevent it from escaping into space. These gases are called greenhouse gases (GHGs).
• July 2023 was the hottest month ever recorded on Earth.
• Global warming has the potential to cause disruptions in the food supply, harm ecosystems and wildlife habitats, and threaten the planet's biodiversity.
• Countries that experience the harshest effects of climate change are often low- and middle-income countries who contribute fewer greenhouse gas emissions than wealthier countries that do not experience the effects so intensely.
• The United States has joined other countries in making commitments to fight climate change, but that commitment has largely depended on the country's leadership.
• Though the administration of President Joe Biden has taken more aggressive steps to combat the climate crisis, critics question whether these steps will meet the administration's ambitious goals and whether those goals are sufficient.

CAUSES OF CLIMATE CHANGE

Earth's atmosphere contains several gases that trap heat from the sun and prevent it from escaping into space. This phenomenon is known as the greenhouse effect , and the gases are called greenhouse gases (GHGs). The main GHGs in nature are carbon dioxide, methane, and nitrous oxide. Without the greenhouse effect, Earth would be too cold to support life. Over time, the amount of GHGs trapped in Earth's atmosphere has increased significantly, causing worldwide temperatures to rise.

Natural processes on Earth constantly create and destroy GHGs. For example, plant and animal matter decay produce carbon dioxide, which plants then absorb during photosynthesis. This natural cycle stabilizes atmospheric levels of carbon dioxide. Climate change scientists at the National Aeronautics and Space Administration (NASA) and other federal and international agencies recognize that natural factors, including volcanic activity and shifts in the planet's crust, continue to play a role in climate change. However, they generally agree that these factors alone do not explain the substantial rise in Earth's temperature. Natural causes of climate change are referred to as naturogenic , while causes of climate change related to human activity are called anthropogenic .

Earth's vegetation releases and absorbs over two hundred billion metric tons of carbon dioxide annually. Human activities, such as the burning of fossil fuels, add approximately seven billion metric tons per year. Climate scientists believe the cumulative effect of this additional carbon dioxide has had a dramatic impact on the atmosphere. Deforestation has also contributed to this increase by releasing carbon dioxide stored in trees and eliminating forests that would continue to absorb many tons of carbon dioxide. According to the National Oceanic and Atmospheric Administration (NOAA), as of 2023 the amount of carbon dioxide in the atmosphere had increased by 50 percent since the beginning of the Industrial Revolution in Great Britain in the eighteenth century.

Increased levels of other GHGs, such as nitrous oxide and methane, have also resulted from human activity. Several agricultural and industrial processes, such as the use of certain fertilizers in farming, produce extensive amounts nitrous oxide. Methane emissions come from fossil fuel production, landfills, and livestock. Though much smaller quantities of these gases exist in Earth's atmosphere, some scientists believe they cause more harm than carbon dioxide. Methane, for example, is about twenty-one times as potent as carbon dioxide at trapping heat. Humans have also created and released GHGs that do not occur in nature. These include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). These gases, released during industrial processes such as aluminum production and electrical transmission, trap thousands of times more heat in the atmosphere than carbon dioxide.

CLIMATE CHANGE PREDICTIONS

A broad consensus exists in the scientific community that the consequences of climate change may be devastating, though the exact nature of the changes is difficult to predict. No model to chart climate patterns has had complete accuracy. For instance, most climate models failed to predict a slowdown in rising temperatures starting in 1998 and ending in 2012. The slowdown was attributed to volcanic eruptions that blocked out the sun and cooled temperatures, low levels of solar activity, and naturally occurring variability. Similarly, some predictions have underestimated threats.

In its initial assessment of rising sea levels in 1990, the IPCC initially anticipated a sea level rise of 1.9 millimeters per year from that year onward. However, as of 2023, the IPCC reports that sea levels rose at a rate of 3.7 millimeters per year between 2006 and 2018. Sea level rise contributes to increased flooding and the damage caused by extreme storms such as hurricanes in coastal cities. The IPCC predicts that sea level rise could threaten as many as one billion people living in low-lying cities and communities by 2041, noting the threats to livelihoods, cultural heritage, and the existence of many island nations.

US PUBLIC OPINION ON CLIMATE CHANGE

The effects of human activities on global warming and climate change are acknowledged and accepted by most people in the United States. According to annual polls conducted by Gallup since 2001, the public's beliefs in anthropogenic climate change has increased. In 2023, 62 percent of Americans accepted that human activities cause climate change (up from 61 percent in 2001), 60 percent believed that the effects have begun (up from 54 percent), and 46 percent stated that global warming will soon pose a serious threat (up from 31 percent).

Researchers have observed a strong correlation between Americans' political affiliations and their acceptance of climate science and levels of concern about global warming. In 2023, about 85 percent of Democrats believed the effects of global warming were already apparent, and 88 percent believed humans caused them. In comparison, only 33 percent of Republicans agreed with the first statement and 29 percent agreed with the second. Most independents believed both statements (61 and 66 percent, respectively). However, further analysis by Gallup in 2022 revealed that Republicans under age fifty-five expressed greater concern about global warming than those age fifty-five and older but still significantly fewer than Democrats or Independents of any age group.

EFFECTS OF GLOBAL WARMING

The potential consequences of global warming remain an issue of great debate and uncertainty. However, most experts predict dramatic and severe problems for future generations. Warmer oceans could result in stronger and more frequent hurricanes. As temperatures climb, some regions could experience frequent heat waves that bring devastating droughts and wildfires. In the United States, the 2023 summer season experienced a series of heat waves that broke temperature records in different parts of the country, particularly in Washington and Oregon. In July 2023, heat waves also affected many countries in the Northern Hemisphere, including Canada, China, and some European countries. NASA has confirmed that July 2023 was the hottest month ever recorded on Earth by a significant margin, identifying global warming as the principal causal factor.

Climate change has been linked to severe, exceptional droughts across several western states, including Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, Oregon, Utah, and Washington. Climate scientists refer to this phenomenon a "megadrought," and it has contributed to massive wildfires in the first decades of the twenty-first century.

From 2018 to 2021, California and Oregon endured massive wildfires that burned millions of acres and led to the displacement of thousands of residents, widespread destruction of property, and the deaths of dozens of people. California had a record-breaking wildfire season in 2020, including the state's first gigafire —a blaze that burned over one million acres of land. By the end of the year, wildfires burned more than four million acres throughout the state. Though wildfires were less frequent throughout the United States from 2022 to 2023 than in the preceding several years, the effects of global warming and the federal and state governments' lack of emergency preparedness led to one of the deadliest wildfires in recorded history. In August 2023 a small brush fire that a broken powerline may have caused started burning just outside the town of Lahaina on the island of Maui in Hawaii. In just a few minutes, winds blew the fire toward town, devouring wooden buildings, telephone and electric power lines, and water pipes. Without enough water pressure, Lahaina's fire department failed to contain the wildfire, and with the town's communication and power systems down, residents were not immediately alerted. As of September 2023, authorities had confirmed that ninety-seven people had been killed in the wildfire and thirty-one individuals were still missing in what had become the eleventh deadliest wildfire in world history.

A megadrought could also lead to water shortages. For example, the US government issued its first Tier 1 federal water shortage declaration in August 2021 for the Colorado River. The river provides water for several US states and parts of Mexico. The first cuts to state water supplies took effect in October in Arizona and Nevada. Upon revisiting the issue in August 2022, the government intensified its alarm, raising the classification to a Tier 2 federal water shortage and issuing drastic cuts to state water allowances. In August 2023, the government announced that the Colorado River water shortage would return to Tier 1 in 2024 and that water restrictions would be eased. The government's decision came after an unusually high amount of snowpack formed on the mountains near the Colorado River during the 2022–2023 winter season.

Many coastal areas worldwide could also face severe flooding due to rising sea levels. Low-lying islands in the Pacific Ocean would eventually become uninhabitable. From 1880 to 2022, sea levels rose about eight to nine inches worldwide. The hurricane season of 2017 proved to be the costliest hurricane season since 1900, causing over $265 billion of property damage in the United States and more than three thousand deaths in Florida, Texas, and Puerto Rico. The year 2020 experienced thirty named storms, the most to ever occur in a single hurricane season. The first hurricane to make landfall in 2022 was Hurricane Fiona, which struck Puerto Rico and other Caribbean Islands in September. All of Puerto Rico, which was still recovering from devastating hurricanes in 2017, lost power, and several areas suffered flooding and landslides. Though twenty tropical storms affected the United States during the 2023 hurricane season, only three made landfall. One of them, Hurricane Idalia, was the strongest hurricane to hit Florida's Big Bend region since 1950, leaving over $1 billion worth of damages.

Global warming also threatens vulnerable ecosystems and wildlife habitats. Extended periods of drought can turn fertile lands into deserts with little vegetation. Plants and animals may not survive the rapid changes caused by global warming and could become extinct. Over the long term, such changes would negatively affect Earth's biodiversity. Environmental scientists warn that some ecosystems, such as coral reefs and coastal mangrove swamps, will likely disappear entirely.

The climate crisis also threatens to disrupt the global food supply, worsen economic inequality, and create security issues. Some areas might become too dry or too wet to support agriculture. As global warming causes more places to become uninhabitable, such displacement can drive mass migration. Communities struggle to recover from climate disasters, often exacerbating existing problems in those areas. Disputes over access to water have arisen in several states, including those with areas that rely on Colorado River water. Around the world, some water disputes have developed into armed conflicts.

CRITICAL THINKING QUESTIONS

• For what reasons do you think perceptions of anthropogenic climate change vary among Democrats and Republicans in the United States?
• What potential long-term consequences of climate change do you think will be the most difficult to manage? Explain your reasoning.
• In what ways, if at all, do you think the federal government could change its approach to address climate change more effectively? Explain your answer.

INTERNATIONAL RESPONSE AND US POLICY

The scope and global nature of the climate crisis necessitate that countries work together. Because an effective response requires countries to make sacrifices, negotiations to develop a coordinated international response have encountered repeated obstacles. Further, industrialized countries have contributed a disproportionate amount to the crisis. In contrast, less industrialized, lower-income countries have disproportionately felt the effects of the crisis and often lack the resources and infrastructure for climate change mitigation and adaptation.

Since 1995, the UN has hosted annual conferences to discuss climate change as part of its Framework Convention on Climate Change (UNFCCC). In 1997, delegates gathered in Kyoto, Japan, to negotiate an international treaty known as the Kyoto Protocol. This treaty required industrialized countries to reduce their GHG emissions by a certain percentage over five years. As of November 2023, 191 countries and the European Union had ratified the Kyoto Protocol. The United States has not ratified the agreement, citing concerns that it does not impose restrictions on China and India. Canada withdrew in 2011.

In 2015, world leaders set new climate goals at the UNFCCC conference (COP21) in Paris, France. The resultant Paris Agreement aimed to limit the rise in global temperatures to less than 2°C (3.6°F) above preindustrial levels and provide countries with the tools needed to counteract climate change. President Barack Obama played a leading role in brokering the Paris Agreement and pushed for greater environmental restrictions during his presidency. The Paris Agreement went into effect with the commitment of the United States and seventy-three other parties in November 2016. Obama's successor, Donald Trump, announced in 2017 that the United States would withdraw its support. After a required period, the United States officially withdrew from the agreement in November 2020.

Upon taking office in January 2021, President Joe Biden reentered the country in the Paris Agreement. Biden vowed that his administration would prioritize climate policy and issued several executive orders that made sustainability and addressing climate change important considerations across all federal government agencies. In April 2021, the president hosted a virtual climate summit attended by forty world leaders and pledged that the United States would reduce its carbon emissions to half of 2005 levels by 2030. In June 2022, the Biden administration experienced a setback when the Supreme Court ruled in West Virginia v. Environmental Protection Agency (EPA) that the Clean Air Act did not grant the EPA authority to regulate GHG emissions without Congress passing additional legislation.

In August 2022, Biden signed the Inflation Reduction Act, a law promoting a sustainable green economy by incentivizing emissions reductions, supporting clean energy projects, and requiring the wealthiest individuals and corporations to pay more taxes. Though many advocates celebrated the law as the federal government's most aggressive step to combat the climate crisis, the law has also attracted criticism. Some detractors contend that the law remains insufficient to have a meaningful impact on the climate crisis or its other targets, which include health care costs, worker protections, and inflation. Further, Republicans have framed the law as an undue empowerment of the Internal Revenue Service (IRS), the agency responsible for collecting taxes. Public reception of Biden's climate policies has largely split along party lines. A June 2023 Pew Research Center survey revealed that 76 percent of Democrats approved of Biden's climate policies while 82 percent of Republicans disapproved.

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Global warming and climate change can be stopped if people try harder.

“Nations need to accelerate deployment of existing technologies to lock in and build on the gains of the last three years.”

Dr. Pep Canadell is Executive Director of the Global Carbon Project, Deputy Research Director at Atmosphere and Land Observation Assessment, and a research scientist at CSIRO Marine and Atmospheric Research.

In the following viewpoint, Canadell argues that recent efforts to improve energy efficiency and increase the use of clean energy have contributed to a stalling in fossil fuel emissions. However, Canadell contends that governments will need to increase their efforts to meet the climate goals established in the 2015 Paris Agreement. He compares the successes and shortcomings of China, the United States, India, Australia, and the European Union in reducing emissions. He examines the practice of storing carbon dioxide underground through carbon capture and storage (CCS) and concludes that thousands of CCS facilities will be necessary to meet climate goals.

Politicians Use Climate Change as an Excuse to Limit Personal Freedom

"Repetition is precisely what we are experiencing in the major media, which have selectively interviewed people who promote the climate change myth."

Cal Thomas is a syndicated columnist and the author of several books, including What Works: Common Sense Solutions for a Stronger America .

In the following viewpoint, Thomas argues that politicians use the issue of climate change as an excuse for the government to interfere in the lives of private citizens. Noting that some climate predictions have overestimated the impact of global warming, the author disputes the widely held belief that global temperatures are rising as a result of human activity. He contends that politicians and the mainstream media encourage public outrage and generate panic over climate change by promoting the opinions and predictions of alarmists while ignoring the views of skeptics.

Renewable Energy Sources Benefit Health, Climate, and the Economy

The Union of Concerned Scientists is a membership organization of citizens and scientists who work together to promote the responsible use of science to improve the world.

Renewable energy sources, such as solar, wind, geothermal, hydroelectric, and biomass, each come with their own set of unique costs and benefits, but overall these cleaner energy sources have overwhelmingly positive effects on the climate, human health, and the economy. Renewable energy sources represent a vast and inexhaustible supply of energy, produce little or no global warming emissions, improve public health and environmental quality, help stabilize energy prices, create jobs and other economic benefits, and contribute to a more reliable and resilient energy system. The costs of renewable energy have declined in recent years and are projected to continue decreasing, making renewables more accessible and affordable for consumers than ever.

Biomass Power Plants Produce Just as Much Pollution as Coal-Fired Power Plants

"There is no quicker way to move carbon into the atmosphere—the opposite of what we want—than through utility-scale biomass energy plants that burn millions of trees per year."

In the following viewpoint, Gordon Clark and Mary Booth point out that although biomass energy has been promoted as environmentally friendly, new and proposed biomass power plants emit just as much pollution and carbon dioxide as those using fossil fuels, sometimes even more. The arguments favoring biomass power plants as a renewable energy source are not valid, they say; recent studies have shown this, and some states are eliminating subsidies and tightening regulations requiring efficiency. The authors speculate whether the Environmental Protection Agency will take federal action and formulate rules that make biomass power plants responsible for the greenhouse gases they release. Booth is the director of the Partnership for Policy Integrity, and Clark is its communications director.

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• ENVIRONMENT

How global warming is disrupting life on Earth

The signs of global warming are everywhere, and are more complex than just climbing temperatures.

Our planet is getting hotter. Since the Industrial Revolution—an event that spurred the use of fossil fuels in everything from power plants to transportation—Earth has warmed by 1 degree Celsius, about 2 degrees Fahrenheit.  

That may sound insignificant, but 2023 was the hottest year on record , and all 10 of the hottest years on record have occurred in the past decade.  

Global warming and climate change are often used interchangeably as synonyms, but scientists prefer to use “climate change” when describing the complex shifts now affecting our planet’s weather and climate systems.  

Climate change encompasses not only rising average temperatures but also natural disasters, shifting wildlife habitats, rising seas , and a range of other impacts. All of these changes are emerging as humans continue to add heat-trapping greenhouse gases , like carbon dioxide and methane, to the atmosphere.

What causes global warming?

When fossil fuel emissions are pumped into the atmosphere, they change the chemistry of our atmosphere, allowing sunlight to reach the Earth but preventing heat from being released into space. This keeps Earth warm, like a greenhouse, and this warming is known as the greenhouse effect .  

Carbon dioxide is the most commonly found greenhouse gas and about 75 percent of all the climate warming pollution in the atmosphere. This gas is a product of producing and burning oil, gas, and coal. About a quarter of Carbon dioxide also results from land cleared for timber or agriculture.  

Methane is another common greenhouse gas. Although it makes up only about 16 percent of emissions, it's roughly 25 times more potent than carbon dioxide and dissipates more quickly. That means methane can cause a large spark in warming, but ending methane pollution can also quickly limit the amount of atmospheric warming. Sources of this gas include agriculture (mostly livestock), leaks from oil and gas production, and waste from landfills.  

What are the effects of global warming?  

One of the most concerning impacts of global warming is the effect warmer temperatures will have on Earth's polar regions and mountain glaciers. The Arctic is warming four times faster than the rest of the planet. This warming reduces critical ice habitat and it disrupts the flow of the jet stream, creating more unpredictable weather patterns around the globe.  

( Learn more about the jet stream. )

A warmer planet doesn't just raise temperatures. Precipitation is becoming more extreme as the planet heats. For every degree your thermometer rises, the air holds about seven percent more moisture. This increase in moisture in the atmosphere can produce flash floods, more destructive hurricanes, and even paradoxically, stronger snow storms.  

The world's leading scientists regularly gather to review the latest research on how the planet is changing. The results of this review is synthesized in regularly published reports known as the Intergovernmental Panel on Climate Change (IPCC) reports.  

A recent report outlines how disruptive a global rise in temperature can be:

• Coral reefs are now a highly endangered ecosystem. When corals face environmental stress, such as high heat, they expel their colorful algae and turn a ghostly white, an effect known as coral bleaching . In this weakened state, they more easily die.  
• Trees are increasingly dying from drought , and this mass mortality is reshaping forest ecosystems.
• Rising temperatures and changing precipitation patterns are making wildfires more common and more widespread. Research shows they're even moving into the eastern U.S. where fires have historically been less common.
• Hurricanes are growing more destructive and dumping more rain, an effect that will result in more damage. Some scientists say we even need to be preparing for Cat 6 storms . (The current ranking system ends at Cat 5.)

How can we limit global warming?  

Limiting the rising in global warming is theoretically achievable, but politically, socially, and economically difficult.  

Those same sources of greenhouse gas emissions must be limited to reduce warming. For example, oil and gas used to generate electricity or power industrial manufacturing will need to be replaced by net zero emission technology like wind and solar power. Transportation, another major source of emissions, will need to integrate more electric vehicles, public transportation, and innovative urban design, such as safe bike lanes and walkable cities.  

( Learn more about solutions to limit global warming. )

One global warming solution that was once considered far fetched is now being taken more seriously: geoengineering. This type of technology relies on manipulating the Earth's atmosphere to physically block the warming rays of the sun or by sucking carbon dioxide straight out of the sky.

Restoring nature may also help limit warming. Trees, oceans, wetlands, and other ecosystems help absorb excess carbon—but when they're lost, so too is their potential to fight climate change.  

Ultimately, we'll need to adapt to warming temperatures, building homes to withstand sea level rise for example, or more efficiently cooling homes during heat waves.  

Related Topics

• CLIMATE CHANGE
• ENVIRONMENT AND CONSERVATION
• POLAR REGIONS

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View of ExxonMobil storage tanks of the petrochemical industry in the port of Rotterdam, Netherlands.

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Alice McCarthy

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Research shows that company modeled and predicted global warming with ‘shocking skill and accuracy’ starting in the 1970s

Projections created internally by ExxonMobil starting in the late 1970s on the impact of fossil fuels on climate change were very accurate, even surpassing those of some academic and governmental scientists, according to an analysis published Thursday in Science by a team of Harvard-led researchers. Despite those forecasts, team leaders say, the multinational energy giant continued to sow doubt about the gathering crisis.

In “Assessing ExxonMobil’s Global Warming Projections,” researchers from Harvard and the Potsdam Institute for Climate Impact Research show for the first time the accuracy of previously unreported forecasts created by company scientists from 1977 through 2003. The Harvard team discovered that Exxon researchers created a series of remarkably reliable models and analyses projecting global warming from carbon dioxide emissions over the coming decades. Specifically, Exxon projected that fossil fuel emissions would lead to 0.20 degrees Celsius of global warming per decade, with a margin of error of 0.04 degrees — a trend that has been proven largely accurate.

“This paper is the first ever systematic assessment of a fossil fuel company’s climate projections, the first time we’ve been able to put a number on what they knew,” said Geoffrey Supran, lead author and former research fellow in the History of Science at Harvard. “What we found is that between 1977 and 2003, excellent scientists within Exxon modeled and predicted global warming with, frankly, shocking skill and accuracy only for the company to then spend the next couple of decades denying that very climate science.”

“This paper is the first ever systematic assessment of a fossil fuel company’s climate projections, the first time we’ve been able to put a number on what they knew,” said Geoffrey Supran, lead author.

File photo by Stephanie Mitchell/Harvard Staff Photographer

“We thought this was a unique opportunity to understand what Exxon knew about this issue and what level of scientific understanding they had at the time,” added co-author Naomi Oreskes , Henry Charles Lea Professor of the History of Science whose work looks at the causes and effects of climate change denial. “We found that not only were their forecasts extremely skillful, but they were also often more skillful than forecasts made by independent academic and government scientists at the exact same time.”

Allegations that oil company executives sought to mislead the public about the industry’s role in climate change have drawn increasing scrutiny in recent years, including lawsuits by several states and cities and a recent high profile U.S. House committee investigation.

Harvard’s scientists used established Intergovernmental Panel on Climate Change (IPCC) statistical techniques to test the performance of Exxon’s models. They found that, depending on the metric used, 63-83 percent of the global warming projections reported by Exxon scientists were consistent with actual temperatures over time. Moreover, the corporation’s own projections had an average “skill score” of 72 percent, plus or minus 6 percent, with the highest scoring 99 percent. A skill score relates to how well a forecast compares to what happens in real life. For comparison, NASA scientist James Hansen’s global warming predictions presented to the U.S. Congress in 1988 had scores from 38 to 66 percent.

The researchers report that Exxon scientists correctly dismissed the possibility of a coming ice age, accurately predicted that human-caused global warming would first be detectable in the year 2000, plus or minus five years, and reasonably estimated how much CO 2 would lead to dangerous warming.

The current debate about when Exxon knew about the impact on climate change carbon emissions began in 2015 following news reports of internal company documents describing the multinational’s early knowledge of climate science.  Exxon disagreed with the reports, even providing a link to internal studies and memos from their own scientists and suggesting that interested parties should read them and make up their own minds.

“That’s exactly what we did,” said Supran, who is now at the University of Miami. Together, he and Oreskes spent a year researching those documents and in 2017 published a series of three papers analyzing Exxon’s 40-year history of climate communications . They were able to show there was a systematic discrepancy between what Exxon was saying internally and in academic circles versus what they were telling the public. “That led us to conclude that they had quantifiably misled the public, by essentially contributing quietly to climate science and yet loudly promoting doubt about that science,” said Supran.

“I think this new study is the smoking gun, the proof, because it shows the degree of understanding … this really deep, really sophisticated, really skillful understanding that was obscured by what came next,” said Harvard Professor Naomi Oreskes.

Harvard file photo

In 2021, the team published a new study in One Earth using algorithmic techniques to identify ways in which ExxonMobil used increasingly subtle but systematic language to shape the way the public talks and thinks about climate change — often in misleading ways.

These findings were hardly a surprise to Oreskes, given her long history of studying climate communications from fossil fuel companies, work that drew national attention with her 2010 bestseller, “Merchants of Doubt.” In it she and co-author, Caltech researcher Erik Conway, argued that Exxon was aware of the threat of carbon emissions on climate change yet waged a disinformation campaign about the problem.  Despite the book’s popularity and the peer-reviewed papers with Supran, however, some continued to wonder whether she could prove the effect these campaigns had, if they indeed made a difference.

“I think this new study is the smoking gun, the proof, because it shows the degree of understanding … this really deep, really sophisticated, really skillful understanding that was obscured by what came next,” Oreskes said. “It proves a point I’ve argued for years that ExxonMobil scientists knew about this problem to a shockingly fine degree as far back as the 1980s, but company spokesmen denied, challenged, and obscured this science, starting in the late 1980s/early 1990s.”

Added Supran: “Our analysis here I think seals the deal on that matter. We now have totally unimpeachable evidence that Exxon accurately predicted global warming years before it turned around and publicly attacked climate science and scientists.”

The authors of this research were supported by a Rockefeller Family Fund grant and Harvard University Faculty Development funds.

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Global Warming

Throughout its long history, Earth has warmed and cooled time and again. Climate has changed when the planet received more or less sunlight due to subtle shifts in its orbit, as the atmosphere or surface changed, or when the Sun’s energy varied. But in the past century, another force has started to influence Earth’s climate: humanity.

(NASA astronaut photograph ISS022-E-6674. )

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.

How Does Today’s Warming Compare to Past Climate Change?

Earth has experienced climate change in the past without help from humanity. But the current climatic warming is occurring much more rapidly than past warming events.

Why Do Scientists Think Current Warming Isn’t Natural?

In Earth’s history before the Industrial Revolution, Earth’s climate changed due to natural causes unrelated to human activity. These 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.

How Much More Will Earth Warm?

Models predict that as the world consumes ever more fossil fuel, greenhouse gas concentrations will continue to rise, and Earth’s average surface temperature will rise with them. Based on plausible emission scenarios, average surface temperatures could rise between 2°C and 6°C by the end of the 21st century. Some of this warming will occur even if future greenhouse gas emissions are reduced, because the Earth system has not yet fully adjusted to environmental changes we have already made.

How Will Earth Respond to Warming Temperatures?

The impact of global warming is far greater than just increasing temperatures. Warming modifies rainfall patterns, amplifies coastal erosion, lengthens the growing season in some regions, melts ice caps and glaciers, and alters the ranges of some infectious diseases. Some of these changes are already occurring.

References and Related Resources

Throughout its long history, Earth has warmed and cooled time and again. Climate has changed when the planet received more or less sunlight due to subtle shifts in its orbit, as the atmosphere or surface changed, or when the Sun’s energy varied. But in the past century, another force has started to influence Earth’s climate: humanity

How does this warming compare to previous changes in Earth’s climate? How can we be certain that human-released greenhouse gases are causing the warming? How much more will the Earth warm? How will Earth respond? Answering these questions is perhaps the most significant scientific challenge of our time.

Global warming is the unusually rapid increase in Earth’s average surface temperature over the past century primarily due to the greenhouse gases released as people burn fossil fuels. The global average surface temperature rose 0.6 to 0.9 degrees Celsius (1.1 to 1.6° F) between 1906 and 2005, and the rate of temperature increase has nearly doubled in the last 50 years. Temperatures are certain to go up further.

Despite ups and downs from year to year, global average surface temperature is rising. By the beginning of the 21st century, Earth’s temperature was roughly 0.5 degrees Celsius above the long-term (1951–1980) average. (NASA figure adapted from Goddard Institute for Space Studies Surface Temperature Analysis. )

Earth’s natural greenhouse effect

Earth’s temperature begins with the Sun. Roughly 30 percent of incoming sunlight is reflected back into space by bright surfaces like clouds and ice. Of the remaining 70 percent, most is absorbed by the land and ocean, and the rest is absorbed by the atmosphere. The absorbed solar energy heats our planet.

As the rocks, the air, and the seas warm, they radiate “heat” energy (thermal infrared radiation). From the surface, this energy travels into the atmosphere where much of it is absorbed by water vapor and long-lived greenhouse gases such as carbon dioxide and methane.

When they absorb the energy radiating from Earth’s surface, microscopic water or greenhouse gas molecules turn into tiny heaters— like the bricks in a fireplace, they radiate heat even after the fire goes out. They radiate in all directions. The energy that radiates back toward Earth heats both the lower atmosphere and the surface, enhancing the heating they get from direct sunlight.

This absorption and radiation of heat by the atmosphere—the natural greenhouse effect—is beneficial for life on Earth. If there were no greenhouse effect, the Earth’s average surface temperature would be a very chilly -18°C (0°F) instead of the comfortable 15°C (59°F) that it is today.

See Climate and Earth’s Energy Budget to read more about how sunlight fuels Earth’s climate.

The enhanced greenhouse effect

What has scientists concerned now is that over the past 250 years, humans have been artificially raising the concentration of greenhouse gases in the atmosphere at an ever-increasing rate, mostly by burning fossil fuels, but also from cutting down carbon-absorbing forests. Since the Industrial Revolution began in about 1750, carbon dioxide levels have increased nearly 38 percent as of 2009 and methane levels have increased 148 percent.

Increases in concentrations of carbon dioxide (top) and methane (bottom) coincided with the start of the Industrial Revolution in about 1750. Measurements from Antarctic ice cores (green lines) combined with direct atmospheric measurements (blue lines) show the increase of both gases over time. (NASA graphs by Robert Simmon, based on data from the NOAA Paleoclimatology and Earth System Research Laboratory. )

The atmosphere today contains more greenhouse gas molecules, so more of the infrared energy emitted by the surface ends up being absorbed by the atmosphere. Since some of the extra energy from a warmer atmosphere radiates back down to the surface, Earth’s surface temperature rises. By increasing the concentration of greenhouse gases, we are making Earth’s atmosphere a more efficient greenhouse.

How is Today’s Warming Different from the Past?

Earth has experienced climate change in the past without help from humanity. We know about past climates because of evidence left in tree rings, layers of ice in glaciers, ocean sediments, coral reefs, and layers of sedimentary rocks. For example, bubbles of air in glacial ice trap tiny samples of Earth’s atmosphere, giving scientists a history of greenhouse gases that stretches back more than 800,000 years. The chemical make-up of the ice provides clues to the average global temperature.

See the Earth Observatory’s series Paleoclimatology for details about how scientists study past climates.

Glacial ice and air bubbles trapped in it (top) preserve an 800,000-year record of temperature & carbon dioxide. Earth has cycled between ice ages (low points, large negative anomalies) and warm interglacials (peaks). (Photograph courtesy National Snow & Ice Data Center. NASA graph by Robert Simmon, based on data from Jouzel et al., 2007. )

Using this ancient evidence, scientists have built a record of Earth’s past climates, or “paleoclimates.” The paleoclimate record combined with global models shows past ice ages as well as periods even warmer than today. But the paleoclimate record also reveals that the current climatic warming is occurring much more rapidly than past warming events.

As the Earth moved out of ice ages over the past million years, the global temperature rose a total of 4 to 7 degrees Celsius over about 5,000 years. In the past century alone, the temperature has climbed 0.7 degrees Celsius, roughly ten times faster than the average rate of ice-age-recovery warming.

Temperature histories from paleoclimate data (green line) compared to the history based on modern instruments (blue line) suggest that global temperature is warmer now than it has been in the past 1,000 years, and possibly longer. (Graph adapted from Mann et al., 2008. )

Models predict that Earth will warm between 2 and 6 degrees Celsius in the next century. When global warming has happened at various times in the past two million years, it has taken the planet about 5,000 years to warm 5 degrees. The predicted rate of warming for the next century is at least 20 times faster. This rate of change is extremely unusual.

Is Current Warming Natural?

In Earth’s history before the Industrial Revolution, Earth’s climate changed due to natural causes not related to human activity. Most often, global climate has changed because of variations in sunlight. Tiny wobbles in Earth’s orbit altered when and where sunlight falls on Earth’s surface. Variations in the Sun itself have alternately increased and decreased the amount of solar energy reaching Earth. Volcanic eruptions have generated particles that reflect sunlight, brightening the planet and cooling the climate. Volcanic activity has also, in the deep past, increased greenhouse gases over millions of years, contributing to episodes of global warming.

A biographical sketch of Milutin Milankovitch describes how changes in Earth’s orbit affects its climate.

These 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. We know this because scientists closely monitor the natural and human activities that influence climate with a fleet of satellites and surface instruments.

Remote meteorological stations (left) and orbiting satellites (right) help scientists monitor the causes and effects of global warming. [Images courtesy NOAA Network for the Detection of Atmospheric Composition Change (left) and Environmental Visualization Laboratory (right).]

NASA satellites record a host of vital signs including atmospheric aerosols (particles from both natural sources and human activities, such as factories, fires, deserts, and erupting volcanoes), atmospheric gases (including greenhouse gases), energy radiated from Earth’s surface and the Sun, ocean surface temperature changes, global sea level, the extent of ice sheets, glaciers and sea ice, plant growth, rainfall, cloud structure, and more.

On the ground, many agencies and nations support networks of weather and climate-monitoring stations that maintain temperature, rainfall, and snow depth records, and buoys that measure surface water and deep ocean temperatures. Taken together, these measurements provide an ever-improving record of both natural events and human activity for the past 150 years.

Scientists integrate these measurements into climate models to recreate temperatures recorded over the past 150 years. Climate model simulations that consider only natural solar variability and volcanic aerosols since 1750—omitting observed increases in greenhouse gases—are able to fit the observations of global temperatures only up until about 1950. After that point, the decadal trend in global surface warming cannot be explained without including the contribution of the greenhouse gases added by humans.

Though people have had the largest impact on our climate since 1950, natural changes to Earth’s climate have also occurred in recent times. For example, two major volcanic eruptions, El Chichon in 1982 and Pinatubo in 1991, pumped sulfur dioxide gas high into the atmosphere. The gas was converted into tiny particles that lingered for more than a year, reflecting sunlight and shading Earth’s surface. Temperatures across the globe dipped for two to three years.

Although Earth’s temperature fluctuates naturally, human influence on climate has eclipsed the magnitude of natural temperature changes over the past 120 years. Natural influences on temperature—El Niño, solar variability, and volcanic aerosols—have varied approximately plus and minus 0.2° C (0.4° F), (averaging to about zero), while human influences have contributed roughly 0.8° C (1° F) of warming since 1889. (Graphs adapted from Lean et al., 2008.)

Although volcanoes are active around the world, and continue to emit carbon dioxide as they did in the past, the amount of carbon dioxide they release is extremely small compared to human emissions. On average, volcanoes emit between 130 and 230 million tonnes of carbon dioxide per year. By burning fossil fuels, people release in excess of 100 times more, about 26 billion tonnes of carbon dioxide, into the atmosphere every year (as of 2005). As a result, human activity overshadows any contribution volcanoes may have made to recent global warming.

Changes in the brightness of the Sun can influence the climate from decade to decade, but an increase in solar output falls short as an explanation for recent warming. NASA satellites have been measuring the Sun’s output since 1978. The total energy the Sun radiates varies over an 11-year cycle. During solar maxima, solar energy is approximately 0.1 percent higher on average than it is during solar minima.

The transparent halo known as the solar corona changes between solar maximum (left) and solar minimum (right). (NASA Extreme Ultraviolet Telescope images from the SOHO Data Archive. )

Each cycle exhibits subtle differences in intensity and duration. As of early 2010, the solar brightness since 2005 has been slightly lower, not higher, than it was during the previous 11-year minimum in solar activity, which occurred in the late 1990s. This implies that the Sun’s impact between 2005 and 2010 might have been to slightly decrease the warming that greenhouse emissions alone would have caused.

Satellite measurements of daily (light line) and monthly average (dark line) total solar irradiance since 1979 have not detected a clear long-term trend. (NASA graph by Robert Simmon, based on data from the ACRIM Science Team. )

Scientists theorize that there may be a multi-decadal trend in solar output, though if one exists, it has not been observed as yet. Even if the Sun were getting brighter, however, the pattern of warming observed on Earth since 1950 does not match the type of warming the Sun alone would cause. When the Sun’s energy is at its peak (solar maxima), temperatures in both the lower atmosphere (troposphere) and the upper atmosphere (stratosphere) become warmer. Instead, observations show the pattern expected from greenhouse gas effects: Earth’s surface and troposphere have warmed, but the stratosphere has cooled.

Satellite measurements show warming in the troposphere (lower atmosphere, green line) but cooling in the stratosphere (upper atmosphere, red line). This vertical pattern is consistent with global warming due to increasing greenhouse gases, but inconsistent with warming from natural causes. (Graph by Robert Simmon, based on data from Remote Sensing Systems, sponsored by the NOAA Climate and Global Change Program.)

The stratosphere gets warmer during solar maxima because the ozone layer absorbs ultraviolet light; more ultraviolet light during solar maxima means warmer temperatures. Ozone depletion explains the biggest part of the cooling of the stratosphere over recent decades, but it can’t account for all of it. Increased concentrations of carbon dioxide in the troposphere and stratosphere together contribute to cooling in the stratosphere.

To further explore the causes and effects of global warming and to predict future warming, scientists build climate models—computer simulations of the climate system. Climate models are designed to simulate the responses and interactions of the oceans and atmosphere, and to account for changes to the land surface, both natural and human-induced. They comply with fundamental laws of physics—conservation of energy, mass, and momentum—and account for dozens of factors that influence Earth’s climate.

Though the models are complicated, rigorous tests with real-world data hone them into powerful tools that allow scientists to explore our understanding of climate in ways not otherwise possible. By experimenting with the models—removing greenhouse gases emitted by the burning of fossil fuels or changing the intensity of the Sun to see how each influences the climate—scientists use the models to better understand Earth’s current climate and to predict future climate.

The models predict that as the world consumes ever more fossil fuel, greenhouse gas concentrations will continue to rise, and Earth’s average surface temperature will rise with them. Based on a range of plausible emission scenarios, average surface temperatures could rise between 2°C and 6°C by the end of the 21st century.

Model simulations by the Intergovernmental Panel on Climate Change estimate that Earth will warm between two and six degrees Celsius over the next century, depending on how fast carbon dioxide emissions grow. Scenarios that assume that people will burn more and more fossil fuel provide the estimates in the top end of the temperature range, while scenarios that assume that greenhouse gas emissions will grow slowly give lower temperature predictions. The orange line provides an estimate of global temperatures if greenhouse gases stayed at year 2000 levels. (©2007 IPCC WG1 AR-4.)

Climate Feedbacks

Greenhouse gases are only part of the story when it comes to global warming. Changes to one part of the climate system can cause additional changes to the way the planet absorbs or reflects energy. These secondary changes are called climate feedbacks, and they could more than double the amount of warming caused by carbon dioxide alone. The primary feedbacks are due to snow and ice, water vapor, clouds, and the carbon cycle.

Snow and ice

Perhaps the most well known feedback comes from melting snow and ice in the Northern Hemisphere. Warming temperatures are already melting a growing percentage of Arctic sea ice, exposing dark ocean water during the perpetual sunlight of summer. Snow cover on land is also dwindling in many areas. In the absence of snow and ice, these areas go from having bright, sunlight-reflecting surfaces that cool the planet to having dark, sunlight-absorbing surfaces that bring more energy into the Earth system and cause more warming.

Canada’s Athabasca Glacier has been shrinking by about 15 meters per year. In the past 125 years, the glacier has lost half its volume and has retreated more than 1.5 kilometers. As glaciers retreat, sea ice disappears, and snow melts earlier in the spring, the Earth absorbs more sunlight than it would if the reflective snow and ice remained. (Photograph ©2005 Hugh Saxby. )

Water Vapor

The largest feedback is water vapor. Water vapor is a strong greenhouse gas. In fact, because of its abundance in the atmosphere, water vapor causes about two-thirds of greenhouse warming, a key factor in keeping temperatures in the habitable range on Earth. But as temperatures warm, more water vapor evaporates from the surface into the atmosphere, where it can cause temperatures to climb further.

The question that scientists ask is, how much water vapor will be in the atmosphere in a warming world? The atmosphere currently has an average equilibrium or balance between water vapor concentration and temperature. As temperatures warm, the atmosphere becomes capable of containing more water vapor, and so water vapor concentrations go up to regain equilibrium. Will that trend hold as temperatures continue to warm?

The amount of water vapor that enters the atmosphere ultimately determines how much additional warming will occur due to the water vapor feedback. The atmosphere responds quickly to the water vapor feedback. So far, most of the atmosphere has maintained a near constant balance between temperature and water vapor concentration as temperatures have gone up in recent decades. If this trend continues, and many models say that it will, water vapor has the capacity to double the warming caused by carbon dioxide alone.

Closely related to the water vapor feedback is the cloud feedback. Clouds cause cooling by reflecting solar energy, but they also cause warming by absorbing infrared energy (like greenhouse gases) from the surface when they are over areas that are warmer than they are. In our current climate, clouds have a cooling effect overall, but that could change in a warmer environment.

Clouds can both cool the planet (by reflecting visible light from the sun) and warm the planet (by absorbing heat radiation emitted by the surface). On balance, clouds slightly cool the Earth. (NASA Astronaut Photograph STS31-E-9552 courtesy Johnson space Center Earth Observations Lab. )

If clouds become brighter, or the geographical extent of bright clouds expands, they will tend to cool Earth’s surface. Clouds can become brighter if more moisture converges in a particular region or if more fine particles (aerosols) enter the air. If fewer bright clouds form, it will contribute to warming from the cloud feedback.

See Ship Tracks South of Alaska to learn how aerosols can make clouds brighter.

Clouds, like greenhouse gases, also absorb and re-emit infrared energy. Low, warm clouds emit more energy than high, cold clouds. However, in many parts of the world, energy emitted by low clouds can be absorbed by the abundant water vapor above them. Further, low clouds often have nearly the same temperatures as the Earth’s surface, and so emit similar amounts of infrared energy. In a world without low clouds, the amount of emitted infrared energy escaping to space would not be too different from a world with low clouds.

Clouds emit thermal infrared (heat) radiation in proportion to their temperature, which is related to altitude. This image shows the Western Hemisphere in the thermal infrared. Warm ocean and land surface areas are white and light gray; cool, low-level clouds are medium gray; and cold, high-altitude clouds are dark gray and black. (NASA image courtesy GOES Project Science. )

High cold clouds, however, form in a part of the atmosphere where energy-absorbing water vapor is scarce. These clouds trap (absorb) energy coming from the lower atmosphere, and emit little energy to space because of their frigid temperatures. In a world with high clouds, a significant amount of energy that would otherwise escape to space is captured in the atmosphere. As a result, global temperatures are higher than in a world without high clouds.

If warmer temperatures result in a greater amount of high clouds, then less infrared energy will be emitted to space. In other words, more high clouds would enhance the greenhouse effect, reducing the Earth’s capability to cool and causing temperatures to warm.

See Clouds and Radiation for a more complete description.

Scientists aren’t entirely sure where and to what degree clouds will end up amplifying or moderating warming, but most climate models predict a slight overall positive feedback or amplification of warming due to a reduction in low cloud cover. A recent observational study found that fewer low, dense clouds formed over a region in the Pacific Ocean when temperatures warmed, suggesting a positive cloud feedback in this region as the models predicted. Such direct observational evidence is limited, however, and clouds remain the biggest source of uncertainty--apart from human choices to control greenhouse gases—in predicting how much the climate will change.

The Carbon Cycle

Increased atmospheric carbon dioxide concentrations and warming temperatures are causing changes in the Earth’s natural carbon cycle that also can feedback on atmospheric carbon dioxide concentration. For now, primarily ocean water, and to some extent ecosystems on land, are taking up about half of our fossil fuel and biomass burning emissions. This behavior slows global warming by decreasing the rate of atmospheric carbon dioxide increase, but that trend may not continue. Warmer ocean waters will hold less dissolved carbon, leaving more in the atmosphere.

About half the carbon dioxide emitted into the air from burning fossil fuels dissolves in the ocean. This map shows the total amount of human-made carbon dioxide in ocean water from the surface to the sea floor. Blue areas have low amounts, while yellow regions are rich in anthropogenic carbon dioxide. High amounts occur where currents carry the carbon-dioxide-rich surface water into the ocean depths. (Map adapted from Sabine et al., 2004.)

See The Ocean’s Carbon Balance on the Earth Observatory.

On land, changes in the carbon cycle are more complicated. Under a warmer climate, soils, especially thawing Arctic tundra, could release trapped carbon dioxide or methane to the atmosphere. Increased fire frequency and insect infestations also release more carbon as trees burn or die and decay.

On the other hand, extra carbon dioxide can stimulate plant growth in some ecosystems, allowing these plants to take additional carbon out of the atmosphere. However, this effect may be reduced when plant growth is limited by water, nitrogen, and temperature. This effect may also diminish as carbon dioxide increases to levels that become saturating for photosynthesis. Because of these complications, it is not clear how much additional carbon dioxide plants can take out of the atmosphere and how long they could continue to do so.

The impact of climate change on the land carbon cycle is extremely complex, but on balance, land carbon sinks will become less efficient as plants reach saturation, where they can no longer take up additional carbon dioxide, and other limitations on growth occur, and as land starts to add more carbon to the atmosphere from warming soil, fires, and insect infestations. This will result in a faster increase in atmospheric carbon dioxide and more rapid global warming. In some climate models, carbon cycle feedbacks from both land and ocean add more than a degree Celsius to global temperatures by 2100.

Emission Scenarios

Scientists predict the range of likely temperature increase by running many possible future scenarios through climate models. Although some of the uncertainty in climate forecasts comes from imperfect knowledge of climate feedbacks, the most significant source of uncertainty in these predictions is that scientists don’t know what choices people will make to control greenhouse gas emissions.

The higher estimates are made on the assumption that the entire world will continue using more and more fossil fuel per capita, a scenario scientists call “business-as-usual.” More modest estimates come from scenarios in which environmentally friendly technologies such as fuel cells, solar panels, and wind energy replace much of today’s fossil fuel combustion.

It takes decades to centuries for Earth to fully react to increases in greenhouse gases. Carbon dioxide, among other greenhouse gases, will remain in the atmosphere long after emissions are reduced, contributing to continuing warming. In addition, as Earth has warmed, much of the excess energy has gone into heating the upper layers of the ocean. Like a hot water bottle on a cold night, the heated ocean will continue warming the lower atmosphere well after greenhouse gases have stopped increasing.

These considerations mean that people won’t immediately see the impact of reduced greenhouse gas emissions. Even if greenhouse gas concentrations stabilized today, the planet would continue to warm by about 0.6°C over the next century because of greenhouses gases already in the atmosphere.

See Earth’s Big Heat Bucket, Correcting Ocean Cooling, and Climate Q&A: If we immediately stopped emitting greenhouse gases, would global warming stop? to learn more about the ocean heat and global warming.

How Will Global Warming Change Earth?

The impact of increased surface temperatures is significant in itself. But global warming will have additional, far-reaching effects on the planet. Warming modifies rainfall patterns, amplifies coastal erosion, lengthens the growing season in some regions, melts ice caps and glaciers, and alters the ranges of some infectious diseases. Some of these changes are already occurring.

Global warming will shift major climate patterns, possibly prolonging and intensifying the current drought in the U.S. Southwest. The white ring of bleached rock on the once-red cliffs that hold Lake Powell indicate the drop in water level over the past decade—the result of repeated winters with low snowfall. (Photograph ©2006 Tigresblanco. )

Changing Weather

For most places, global warming will result in more frequent hot days and fewer cool days, with the greatest warming occurring over land. Longer, more intense heat waves will become more common. Storms, floods, and droughts will generally be more severe as precipitation patterns change. Hurricanes may increase in intensity due to warmer ocean surface temperatures.

Apart from driving temperatures up, global warming is likely to cause bigger, more destructive storms, leading to an overall increase in precipitation. With some exceptions, the tropics will likely receive less rain (orange) as the planet warms, while the polar regions will receive more precipitation (green). White areas indicate that fewer than two-thirds of the climate models agreed on how precipitation will change. Stippled areas reveal where more than 90 percent of the models agreed. (©2007 IPCC WG1 AR-4.)

It is impossible to pin any single unusual weather event on global warming, but emerging evidence suggests that global warming is already influencing the weather. Heat waves, droughts, and intense rain events have increased in frequency during the last 50 years, and human-induced global warming more likely than not contributed to the trend.

Rising Sea Levels

The weather isn’t the only thing global warming will impact: rising sea levels will erode coasts and cause more frequent coastal flooding. Some island nations will disappear. The problem is serious because up to 10 percent of the world’s population lives in vulnerable areas less than 10 meters (about 30 feet) above sea level.

Between 1870 and 2000, the sea level increased by 1.7 millimeters per year on average, for a total sea level rise of 221 millimeters (0.7 feet or 8.7 inches). And the rate of sea level rise is accelerating. Since 1993, NASA satellites have shown that sea levels are rising more quickly, about 3 millimeters per year, for a total sea level rise of 48 millimeters (0.16 feet or 1.89 inches) between 1993 and 2009.

Sea levels crept up about 20 centimeters (7.9 inches) during the twentieth century. Sea levels are predicted to go up between 18 and 59 cm (7.1 and 23 inches) over the next century, though the increase could be greater if ice sheets in Greenland and Antarctica melt more quickly than predicted. Higher sea levels will erode coastlines and cause more frequent flooding. (Graph ©2007 Robert Rohde. )

The Intergovernmental Panel on Climate Change (IPCC) estimates that sea levels will rise between 0.18 and 0.59 meters (0.59 to 1.9 feet) by 2099 as warming sea water expands, and mountain and polar glaciers melt. These sea level change predictions may be underestimates, however, because they do not account for any increases in the rate at which the world’s major ice sheets are melting. As temperatures rise, ice will melt more quickly. Satellite measurements reveal that the Greenland and West Antarctic ice sheets are shedding about 125 billion tons of ice per year—enough to raise sea levels by 0.35 millimeters (0.01 inches) per year. If the melting accelerates, the increase in sea level could be significantly higher.

Impacting Ecosystems

More importantly, perhaps, global warming is already putting pressure on ecosystems, the plants and animals that co-exist in a particular climate zone, both on land and in the ocean. Warmer temperatures have already shifted the growing season in many parts of the globe. The growing season in parts of the Northern Hemisphere became two weeks longer in the second half of the 20th century. Spring is coming earlier in both hemispheres.

This change in the growing season affects the broader ecosystem. Migrating animals have to start seeking food sources earlier. The shift in seasons may already be causing the lifecycles of pollinators, like bees, to be out of synch with flowering plants and trees. This mismatch can limit the ability of both pollinators and plants to survive and reproduce, which would reduce food availability throughout the food chain.

See Buzzing About Climate Change to read more about how the lifecycle of bees is synched with flowering plants.

Warmer temperatures also extend the growing season. This means that plants need more water to keep growing throughout the season or they will dry out, increasing the risk of failed crops and wildfires. Once the growing season ends, shorter, milder winters fail to kill dormant insects, increasing the risk of large, damaging infestations in subsequent seasons.

In some ecosystems, maximum daily temperatures might climb beyond the tolerance of indigenous plant or animal. To survive the extreme temperatures, both marine and land-based plants and animals have started to migrate towards the poles. Those species, and in some cases, entire ecosystems, that cannot quickly migrate or adapt, face extinction. The IPCC estimates that 20-30 percent of plant and animal species will be at risk of extinction if temperatures climb more than 1.5° to 2.5°C.

Impacting People

The changes to weather and ecosystems will also affect people more directly. Hardest hit will be those living in low-lying coastal areas, and residents of poorer countries who do not have the resources to adapt to changes in temperature extremes and water resources. As tropical temperature zones expand, the reach of some infectious diseases, such as malaria, will change. More intense rains and hurricanes and rising sea levels will lead to more severe flooding and potential loss of property and life.

One inevitable consequence of global warming is sea-level rise. In the face of higher sea levels and more intense storms, coastal communities face greater risk of rapid beach erosion from destructive storms like the intense nor’easter of April 2007 that caused this damage. (Photograph ©2007 metimbers2000. )

Hotter summers and more frequent fires will lead to more cases of heat stroke and deaths, and to higher levels of near-surface ozone and smoke, which would cause more ‘code red’ air quality days. Intense droughts can lead to an increase in malnutrition. On a longer time scale, fresh water will become scarcer, especially during the summer, as mountain glaciers disappear, particularly in Asia and parts of North America.

On the flip side, there could be “winners” in a few places. For example, as long as the rise in global average temperature stays below 3 degrees Celsius, some models predict that global food production could increase because of the longer growing season at mid- to high-latitudes, provided adequate water resources are available. The same small change in temperature, however, would reduce food production at lower latitudes, where many countries already face food shortages. On balance, most research suggests that the negative impacts of a changing climate far outweigh the positive impacts. Current civilization—agriculture and population distribution—has developed based on the current climate. The more the climate changes, and the more rapidly it changes, the greater the cost of adaptation.

Ultimately, global warming will impact life on Earth in many ways, but the extent of the change is largely up to us. Scientists have shown that human emissions of greenhouse gases are pushing global temperatures up, and many aspects of climate are responding to the warming in the way that scientists predicted they would. This offers hope. Since people are causing global warming, people can mitigate global warming, if they act in time. Greenhouse gases are long-lived, so the planet will continue to warm and changes will continue to happen far into the future, but the degree to which global warming changes life on Earth depends on our decisions now.

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Climate Science

The science is clear: climate change is happening. We are the cause. We need to act now.

Scientists have studied global warming for more than 100 years. Thousands of experts have tested hypotheses, gathered evidence, constructed models, debated results, and reviewed one another’s work. Thousands of papers are written every year, produced from nearly every leading university and research institution on Earth—from Harvard to NASA and the US Department of Defense.

The consensus couldn’t be clearer. Climate change is happening. It’s caused primarily by the burning of oil, gas, and coal. If we do nothing, the world will become significantly less habitable.

We’ve lost precious time, but if we act now—decisively and dramatically—we still have a chance at avoiding climate change’s most catastrophic impacts.

Global Warming FAQ

When released into the atmosphere, certain gases act like a blanket, preventing heat from escaping. One of the most important heat-trapping gases is carbon dioxide (CO 2 ), which is released when we burn fossil fuels like oil, coal, and gas.

The world currently emits a huge amount of carbon dioxide into the atmosphere every day. Carbon dioxide can trap heat for decades: roughly 20 percent will linger in the atmosphere for around 800 years. Methane, another gas, traps heat in the atmosphere for nearly a dozen years at a more powerful level, before transforming into carbon dioxide to trap heat for decades or even centuries.

The cumulative effect is to raise the planet’s temperature. Heat from the sun that would otherwise escape remains on Earth, warming the oceans, land, and air.

As temperatures increase, the planet changes. The seas rise. Droughts and wildfires grow worse. Extreme weather becomes more common. Eventually, entire regions become uninhabitable.

The more carbon dioxide we produce, the worse these and other impacts become—and the more difficult it is to change direction.

The evidence

Ten Signs of Global Warming

Scientists have taken detailed measurements of carbon dioxide (CO2) levels since the late 1950s. They’ve also gathered in-depth records of past CO2 levels from sources like ice core studies.

The results? Carbon dioxide levels are higher today than any point in at least 800,000 years. The cars we drive, the fuel we burn for electricity and warmth, the food we eat or waste, and the forests we clear are the cause.

Temperature trends from around the world reinforce these findings. Every one of the past 40 years has been warmer than the 20th century average. The 12 warmest years on record have all occurred since 1998. The five warmest were 2014 to 2018. We’ve already warmed the planet by 1 degree C (1.7ºF).

Climate models successfully forecast these temperature increases, as well as other impacts like sea level rise and ocean acidification. The models now suggest that we need immediate, dramatic reductions in our CO2 to avoid catastrophic impacts—and that time is running out.

Science Hub for Climate Litigation

The impacts.

The Science Connecting Extreme Weather to Climate Change

The consequences of climate change are already here. In the United States, chronic flooding threatens coastal communities from Texas to Maine. Mega-storms like Harvey, Maria, and Katrina are increasingly commonplace. Wildfires, heat waves, droughts, and inland flooding continue breaking records.

Without immediate emissions reductions, these impacts will worsen. Globally, food and water shortages could displace hundreds of millions of people, increasing conflict and war. Entire regions of the world may become uninhabitable. Much of what we take for granted today—from productive agricultural land and reliable growing seasons, to coastlines and coral reefs—will change dramatically. Much will be lost.

The world’s leading voice on climate science, the International Panel on Climate Change (IPCC), explains that the worst impacts of climate change could be avoided if we successfully limit global warming to under 1.5ºC to 2ºC.

Doing so will not be easy. Under current emission levels, we’ll likely exceed 3ºC this century. For a fighting chance at 1.5ºC, we need to reach “net zero” global emissions by 2050.

“Net zero” means that all the sources of heat-trapping emissions (such as burning fossil fuels) must come in balance with all the processes that remove heat-trapping gases from the atmosphere (such as the growth of forests). Achieving net zero emissions will require massive changes in the energy, transportation, and food sectors, as well as afforestation and new “negative emissions” technologies (such as direct air capture machines that pull CO2 out of the air).

Fortunately, we have clean energy and clean vehicle technologies today. We have scientific consensus. We know what needs doing. We only need to act.

The UCS Position on a Fossil Fuel Phaseout

Related resources.

The Science and Climate Litigation Webinar Series

Understanding Future Groundwater Sustainability Scenarios

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Drivers of Domestic Wells Vulnerability During Droughts in California's Central Valley

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For scientists at SERC, global warming is more than an idea. It is a reality they have seen and felt. The decade from 2001 to 2010 was the warmest decade on record, and while not all places are feeling the heat equally, on average the temperature of the Earth is climbing.

Around the globe, SERC scientists have watched plants and animals move to new territory as regions grow warmer. Closer to home, they have seen evidence of global warming on SERC’s Maryland campus. Since 1987, the growing season at SERC has become a week longer, enabling the trees to grow larger and faster .

The science is simple: Carbon dioxide and other greenhouse gases trap energy from the sun. As greenhouse gases in the atmosphere continue to spike, more heat energy from the sun remains trapped in the lower atmosphere, where it warms the planet below. Since the Industrial Revolution, the global average temperature has risen by almost 1° Celsius . If nothing changes, by 2100 that figure is likely to pass 2° Celsius, enough to melt ice sheets, drown island communities and strain the water supply of billions of people.

SERC researchers investigate how environments are reacting to global warming now, and how they may respond in the future. For decades, they have tracked the swelling of trees in SERC forests and the northward migration of Florida’s tropical mangroves, no longer held back by winter cold snaps. They have uncovered the possibility of dead zones expanding as oceans warm. They’ve also set up warming experiments to examine how various plants and microbes will behave in a future, warmer climate. Explore the projects below to learn more about their work.

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Nutrient over-enrichment increases the productivity of scrub mangroves, but also decreases their resistance and resilience to hurricane damage.

Nutrient Enrichment Intensifies Hurricane Impact on Mangroves

Warming and elevated CO 2 experiment in the Global Change Research Wetland. Heat lamps warm the plants from above, while cables heat the soil.

Salt Marsh Accretion Response to Temperature eXperiment (SMARTX)

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• Published: 22 May 2023

Quantifying the human cost of global warming

• Timothy M. Lenton   ORCID: orcid.org/0000-0002-6725-7498 1   na1 ,
• Chi Xu   ORCID: orcid.org/0000-0002-1841-9032 2   na1 ,
• Jesse F. Abrams   ORCID: orcid.org/0000-0003-0411-8519 1 ,
• Ashish Ghadiali 1 ,
• Sina Loriani   ORCID: orcid.org/0000-0001-6660-960X 3 ,
• Boris Sakschewski   ORCID: orcid.org/0000-0002-7230-9723 3 ,
• Caroline Zimm   ORCID: orcid.org/0000-0001-5603-1015 4 ,
• Kristie L. Ebi   ORCID: orcid.org/0000-0003-4746-8236 5 ,
• Robert R. Dunn   ORCID: orcid.org/0000-0002-6030-4837 6 ,
• Jens-Christian Svenning   ORCID: orcid.org/0000-0002-3415-0862 7 &
• Marten Scheffer   ORCID: orcid.org/0000-0002-2100-0312 8  

Nature Sustainability volume  6 ,  pages 1237–1247 ( 2023 ) Cite this article

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The costs of climate change are often estimated in monetary terms, but this raises ethical issues. Here we express them in terms of numbers of people left outside the ‘human climate niche’—defined as the historically highly conserved distribution of relative human population density with respect to mean annual temperature. We show that climate change has already put ~9% of people (>600 million) outside this niche. By end-of-century (2080–2100), current policies leading to around 2.7 °C global warming could leave one-third (22–39%) of people outside the niche. Reducing global warming from 2.7 to 1.5 °C results in a ~5-fold decrease in the population exposed to unprecedented heat (mean annual temperature ≥29 °C). The lifetime emissions of ~3.5 global average citizens today (or ~1.2 average US citizens) expose one future person to unprecedented heat by end-of-century. That person comes from a place where emissions today are around half of the global average. These results highlight the need for more decisive policy action to limit the human costs and inequities of climate change.

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The burden of heat-related mortality attributable to recent human-induced climate change

Future heat adaptation and exposure among urban populations and why a prospering economy alone won’t save us

Despite increased pledges and targets to tackle climate change, current policies still leave the world on course for around 2.7 °C end-of-century global warming 1 , 2 , 3 , 4 , 5 above pre-industrial levels—far from the ambitious aim of the Paris Agreement to limit global warming to 1.5 °C. Even fully implementing all 2030 nationally determined contributions, long-term pledges and net zero targets, nearly 2 °C global warming is expected later this century 1 , 2 , 5 . Calls for climate justice highlight the vital need to address the social injustices driven by climate change 6 . But what is the human cost of climate change and who bears it? Existing estimates tend to be expressed in monetary terms 7 , tend to recognize impacts on the rich more than those on the poor (because the rich have more money to lose) and tend to value those living now over those living in the future (because future damages are subject to economic discounting). From an equity standpoint, this is unethical 8 —when life or health are at stake, all people should be considered equal, whether rich or poor, alive or yet to be born.

A growing body of work considers how climate variability and climate change affect morbidity 9 or mortality 10 , 11 , 12 , 13 . Here, we take a complementary, ecological approach, considering exposure to less favourable climate conditions, defined as deviations of human population density with respect to climate from the historically highly conserved distribution—the ‘human climate niche’ 14 . The climate niche of species integrates multiple causal factors including combined 15 effects of physiology 16 and ecology 17 . Humans have adapted physiologically and culturally to a wide range of local climates, but despite this our niche 14 shows a primary peak of population density at a mean annual temperature (MAT) of ~13 °C and a secondary peak at ~27 °C (associated with monsoon climates principally in South Asia). The density of domesticated crops and livestock follow similar distributions 14 , as does gross domestic product, which shares the same independently identified 14 , 18 primary temperature peak (~13 °C). Mortality also increases at both high and low temperatures 10 , 11 , 12 , consistent with the existence of a niche.

Here, we reassess the human climate niche, review its mechanistic basis, link it to temperature extremes, and calculate exposure outside the niche up to present and into the future under different demographic scenarios and levels of global warming. Exposure outside the niche could result in increased morbidity, mortality, adaptation in place or displacement (migration elsewhere). High temperatures have been linked to increased mortality 12 , 13 , decreased labour productivity 19 , decreased cognitive performance 20 , impaired learning 21 , adverse pregnancy outcomes 22 , decreased crop yield potential 9 , increased conflict 23 , 24 , 25 , hate speech 26 , migration 27 and infectious disease spread 9 , 28 , 29 . Climate-related sources of harm not captured by the niche include sea-level rise 30 , 31 .

Reassessing the niche

First, we re-examined how relative population density varies with MAT. Our previous work 14 considered the 2015 population distribution under the 1960–1990 mean climate as a baseline (Extended Data Fig. 1 ). Here, we use the 1980 population distribution (total 4.4 billion) under the 1960–1990 mean climate (Fig. 1a ; ‘1980’) as the reference state. This is a more internally consistent approach, particularly as recent population growth biases towards hotter places. Applying a double-Gaussian fitting, the primary temperature peak is now larger and at a slightly lower temperature (~12 °C), in better agreement with reconstructions from 300, 500 and 6,000 years bp (Extended Data Fig. 1 ). The 1960–1990 interval was globally ~0.3 °C warmer than the 1850–1900 ‘pre-industrial’ level, but closer to mean Holocene temperatures that supported civilizations as we know them (because 1850–1900 was at the end of the Little Ice Age). The smoothed double-Gaussian function fit (Fig. 1a ; ‘1980 fitted’) is referred to from hereon as the ‘temperature niche’. An updated ‘temperature–precipitation niche’ (additionally considering mean annual precipitation; MAP) was also calculated and considered in sensitivity analyses. It shows a marked drop in population density 14 , 32 below 1,000 mm yr −1 MAP. The temperature niche captures a key part of this effect because its minimum at 19–24 °C is associated with dry subtropical climates (Extended Data Fig. 2 ). However, the temperature niche overestimates population density at very low MAP (notably in temperate deserts) and at high MAP (Supplementary Fig. 1 ). Hence, projections with the temperature niche are more conservative than those with the temperature–precipitation niche. By either definition, the niche is largely that of people dependent on farming. The niche of hunter-gatherers is probably broader 33 , 34 , 35 , 36 , as it is not constrained by the niches of domesticated species. This hypothesis is supported by the broader distribution of population density with respect to temperature reconstructed 14 from the ArchaeoGLOBE dataset for 6,000 years bp (when a smaller fraction of total population depended on farming; Extended Data Fig. 1b ).

a , Observed changes from the reference distribution for 1980 population (4.4 billion) under 1960–1990 climate (0.3 °C global warming), to the 2010 population (6.9 billion) under 2000–2020 climate (1.0 °C global warming), together with smooth fitted functions (‘1980 fitted’ is defined as the temperature niche). b , Observed and projected future changes in population density with respect to MAT following SSP2-4.5 leading to ~2.7 °C global warming and peak population 9.5 billion (see Extended Data Table 1 for global warming and population levels at each time). c , Projected population density with respect to MAT for a future world of 9.5 billion people under different levels of global warming (1.5, 1.8, 2.1, 2.4, 2.7 and 3.6 °C), contrasted with the reference distribution (0.3 °C, 1980 population). Data are presented as mean values with the shaded regions corresponding to 5th–95th percentiles.

Mechanisms behind the niche

The human climate niche is shaped by direct effects of climate on us and indirect effects on the species and resources that sustain or afflict us. Direct climate effects include health impacts and changes in behaviour. Human perceptions of thermal comfort evolved 37 to keep us near optimal conditions of 22–26 °C, with well-being declining 38 above 28 °C. Behavioural changes include altering clothing, changing environment (including to indoor environments) and altering work patterns 39 . These can buffer individual exposure to temperature extremes but still affect collective well-being via effects on work. Sometimes uncomfortable conditions are unavoidable. High temperatures can decrease labour productivity 19 , cognitive performance 20 and learning 21 , produce adverse pregnancy outcomes 22 , and increase mortality 10 , 11 , 12 . Exposure to temperatures >40 °C can be lethal 40 , and lethal temperature decreases as humidity increases 12 , 40 . At wet-bulb temperature (WBT) >28 °C, the effectiveness of sweating in cooling the body decreases, and WBT ~35 °C can be fatal 41 , 42 especially for more vulnerable individuals 43 (as the body can no longer cool itself). High temperatures can also trigger conflict 23 , 24 , 25 or migration 27 to lower temperature locations.

Indirect effects of climate occur where climate influences the distribution and abundance of species or resources that sustain or afflict humans. Warmer, wetter conditions tend to favour vectors of human disease 9 , 28 , 29 , 44 . The majority of the world’s population remains directly dependent on access to freshwater and lives within 3 km of a surface freshwater body 14 , 32 , 45 . Around 2 billion people depend on subsistence agriculture and thus the climate niche(s) of their crops. A further 120 million pastoralists depend on their domesticated animals, which as mammals have similar physiological limits to humans 40 , 46 . Despite a globalized food market, most countries pursue food security through localized production. This couples the rest of us to the climate niches of the crops and livestock we consume, which are similar to the niche of humans 14 . High temperatures decrease crop yield potential 9 and warming is spreading key crop pests and pathogens 47 , 48 . Major rainfed crops (maize, rice, wheat) are already migrating 49 , somewhat mitigated by increases in irrigation 49 . This and the historical constancy of the niche (Extended Data Fig. 1a ) suggest technological advancement has limited potential to expand the human climate niche in future.

Calculating exposure

For projections, we assume the temperature niche remains unaltered, and provide three calculations of exposure outside of it: (1) exposure to unprecedented heat; (2) total exposure due to temperature change only; or (3) total exposure due to temperature and demographic change (see Methods). (1) The simplest approach 14 just considers ‘hot exposure’—that is, how many people fall outside the hot edge of the temperature niche. This is calculated 14 for a given climate and population distribution as the percentage of population exposed to MAT ≥29 °C, given that only 0.3% of the 1980 population (12 million) experienced such conditions in the 1960–1990 climate. (2) Total exposure due to temperature change alone 14 considers all areas where temperature increases to a value supporting lower relative population density according to the temperature niche. To calculate this 14 (Extended Data Fig. 3 ), we apply the niche to create a spatial ‘ideal distribution’ of relative population density under a changed climate that maintains the historical distribution with respect to temperature. This is contrasted with the spatial ‘reference distribution’ of population density with respect to the 1960–1990 climate. The difference between the two distributions integrated across space gives the percentage of population exposed outside the niche due to climate only. (3) Demographic change can also expose an increased density of population to a less favourable climate. To provide an upper estimate of population exposure (in %) due to both temperature and demographic change (Extended Data Fig. 3 ), we integrate the difference between the projected spatial ‘assumed distribution’ of population density with respect to temperature and the ‘ideal distribution’.

Linking average temperature to other thermal metrics

MAT has the advantage of data availability for characterizing and projecting the human climate niche—it can be easily derived from observational data, reanalysis or climate model output. However, other metrics with less available data have been proposed to better capture thermal tolerance of humans, including mean maximum temperature 46 (MMT) and WBT 40 . Reassuringly, we find that MAT is very highly correlated with both annual MMT and mean annual WBT (Supplementary Fig. 2 ). Given the importance of extremes, we also considered how the number of days with maximum temperature >40 °C or with WBT >28 °C varies with MAT (Extended Data Fig. 4 ). Potentially lethal 40 exposure to maximum temperature >40 °C starts to increase markedly above MAT ~27 °C, reaching an average of over 75 days a year at MAT ~29 °C (half the longest time experienced in the present world), and almost all locations with MAT ≥29 °C experience a substantial number of days with maximum temperature >40 °C (Extended Data Fig. 4a ). Physiologically challenging exposure to WBT >28 °C starts to increase at MAT >22 °C and exceeds an average of 10 days per year at MAT ≥29 °C (Extended Data Fig. 4b ). Together these results show that MAT provides a good proxy for characterizing thermal tolerance, with MAT ≥29 °C providing a reasonable measure of unprecedented heat exposure, although it does not capture all exposure to temperature extremes.

Changes up to present

We find that noticeable changes in the distribution of population density with respect to temperature have occurred due to temperature and demographic changes from 1980 to 2010 (Fig. 1a ). Considering the 2010 population distribution (total 6.9 billion) under the observed 2000–2020 climate, global warming of 1.0 °C (0.7 °C above 1960–1990) has shifted the primary peak of population density to a slightly higher temperature (~13 °C) compared with 1980, and the bias of population growth towards hot places has the increased population density at the secondary (~27 °C) peak. Greater observed global warming in the cooler higher northern latitudes than the tropics is visible in the changes to the distribution (Fig. 1a ). Hot exposure (MAT ≥29 °C) tripled in percentage terms to 0.9 ± 0.4% (mean ± s.d.; 62 ± 26 million people), 9 ± 1% of the global population have been exposed outside the niche due to temperature change alone and 10 ± 1% from temperature plus demographic change (Fig. 2 ). Thus, global warming of 0.7 °C since 1960–1990 has put 624 ± 70 million people in less favourable temperature conditions, with demographic change adding another 77 million.

a – f , Fraction of population (%; a – c ) and absolute population (billion people; d – f ) exposed to unprecedented temperatures (MAT ≥29 °C; a , d ), left outside the niche due to temperature change only ( b , e ,) and left outside the niche due to temperature change and demographic change ( c , f ) for different SSPs. Calculations are based on MAT averaged over the 20-year intervals and population density distribution at the centre year of the corresponding intervals. Data are presented as mean values with the shaded regions corresponding to the 5th–95th percentiles.

Future exposure

To estimate future exposure, we use an ensemble of eight climate model outputs (Supplementary Table 1 ) and corresponding population projections from four Shared Socioeconomic Pathways 50 (SSPs; Extended Data Table 1 )—scenarios of socioeconomic global changes and associated greenhouse gas emissions up to 2100. The ‘middle of the road’ (SSP2-4.5) pathway provides a useful reference scenario because it produces end-of-century (2081–2100) average global warming of 2.7 (range 2.1–3.5) °C corresponding to the 2.7 (2.0–3.6) °C expected under current policies 1 , and it captures population growth towards a peak of ~9.5 billion in 2070 (then declining to ~9.0 billion in 2100). Global warming and population growth combine to shift relative population density to higher temperature (Fig. 1b ). Hot exposure (Fig. 2a,d ) becomes significant by 2030 at 4 ± 2% or 0.3 ± 0.1 billion as global warming reaches 1.5 °C, and it increases near linearly to 23 ± 9% or 2.1 ± 0.8 billion in 2090 under 2.7 °C global warming. The number of people left outside the niche due to temperature change alone (Fig. 2b,e ) reaches 14 ± 3% or 1.2 ± 0.2 billion by 2030, more than doubling to 29 ± 5% or 2.7 ± 0.5 billion in 2090. The number of people left outside the niche from temperature plus demographic change (Fig. 2c,f ) reaches 25 ± 2% or 2.0 ± 0.2 billion by 2030, and 40 ± 4% or 3.7 ± 0.4 billion by 2090.

Variation across the SSPs

The other three SSPs produce a wide range of global warming (2081–2100) from ~1.8 (1.3–2.4) °C to ~4.4 (3.3–5.7) °C and span a wide range of human development trajectories, from population peaking at ~8.5 billion then declining to ~6.9 billion in 2100 to ongoing growth to ~12.6 billion in 2100 (Extended Data Table 1 ). Both global warming and demographic change alter the distribution of relative population density with respect to temperature (Extended Data Fig. 5 ). By 2090, hot exposure reaches 8–40% or 0.6–4.7 billion across scenarios (Fig. 2a,d ). The number of people left outside the niche due to temperature change only reaches 18–47% or 1.3–4.7 billion (Fig. 2b,e ). Adding in demographic change increases this to 29–53% or 2.2–6.5 billion (Fig. 2c,f ). Estimates of exposure outside the combined temperature–precipitation niche are roughly 20% greater than for the temperature niche alone (Extended Data Fig. 6 ). The ‘fossil-fuelled development’ (SSP5-8.5) pathway exposes the greatest proportion of the population to unprecedented heat or being pushed out of the niche due to climate change alone, but the ‘regional rivalry’ (SSP3-7.0) pathway exposes the greatest proportion of the population due to climate and demographic change combined, and the greatest absolute numbers across all three measures of exposure (Fig. 2 and Extended Data Fig. 6 ).

Controlling for demography

Larger global populations following the SSPs place a greater proportion of people in hotter places, tending to leave more outside the niche (irrespective of global warming). To isolate the effects of climate policy and associated climate change on exposure, we fix the population and its distribution, exploring three different options: (1) 6.9 billion (as in 2010); (2) 9.5 billion (as in SSP2 in 2070); and (3) 11.1 billion (as in SSP3 in 2070). Having controlled for demography, global warming shifts the whole distribution of population density to higher temperatures (Fig. 1c and Extended Data Fig. 7 ). This results in linear relationships (Fig. 3 ) between global warming and the percentage of the population exposed to unprecedented heat or left outside the niche from temperature change only, or temperature change plus demographic change. Hot exposure (Fig. 3a ) starts to become significant above the present level of ~1.2 °C global warming and increases steeply at 11.9 % °C −1 (6.9 billion) to 17.5 % °C −1 (11.1 billion). Exposure due to temperature change alone increases 11.8 % °C −1 above the baseline defined at 0.3 °C global warming (1960–1990; Fig. 3b ). Factoring in demography, for a greater fixed population, the percent exposed is always greater, but the dependence on climate weakens somewhat towards 9.1 % °C −1 (for 11.1 billion). The relationships between global warming and exposure are all steeper for the temperature–precipitation niche (Extended Data Fig. 8a ). The mean temperature experienced by an average person increases with global warming in a manner invariant to demography at +1.5 °C °C −1 (Extended Data Fig. 8b ), consistent with observations and models that the land warms ~1.5 times faster than the global average 51 .

a , Population (%) exposed to unprecedented heat (MAT ≥29 °C) for the different population distributions: 6.9 billion (blue; n  = 65, coefficient = 11.9 % °C −1 , r 2  = 0.83); 9.5 billion (green; n  = 65, coefficient = 13.8 % °C −1 , r 2  = 0.83); and 11.1 billion (red; n  = 65, coefficient = 17.5 % °C −1 , r 2  = 0.83). b , Population (%) exposed outside the temperature niche due to temperature change only (purple; n  = 65, coefficient = 11.8 % °C −1 , forcing intercept at 1960–1990 global warming of 0.3 °C), and due to the combined effects of temperature change and demographic change, for different fixed population distributions: 6.9 billion in 2010 (blue; n  = 65, coefficient = 11.0 % °C −1 , r 2  = 0.83); 9.5 billion following SSP2 in 2070 (green; n  = 65, coefficient = 9.5 % °C −1 , r 2  = 0.84); and 11.1 billion following SSP3 in 2070 (red; n  = 65, coefficient = 9.1 % °C −1 , r 2  = 0.84). The shaded regions correspond to 95% two-sided confidence intervals of the estimated regression coefficients.

Worst-case scenarios

We now focus on a future world of 9.5 billion. When assessing risk it is important to consider worst-case scenarios 52 . If the transient climate response to cumulative emissions is high, current policies could, in the worst case, lead to ~3.6 °C end-of-century global warming 1 (as projected under SSP3-7.0; Extended Data Table 1 ). This results in 34 ± 10% (3.3 ± 0.9 billion) hot exposed, 39 ± 7% (3.7 ± 0.7 billion) left outside the niche from temperature change only and 48 ± 7% (4.5 ± 0.6 billion) when including demographic change (Fig. 3 ). There also remains the possibility that climate policies are not enacted, and the world reverts to fossil-fuelled development (SSP5-8.5), leading to ~4.4 °C end-of-century global warming. This gives 45 ± 7% (4.2 ± 0.7 billion) hot exposed, 47 ± 8% (4.5 ± 0.7 billion) left outside the niche from temperature change only and 55 ± 7% (5.3 ± 0.6 billion) when including demographic change (Fig. 3 ).

Gains from strengthening climate policy

Having controlled for demography, strengthening climate policy reduces exposure (Figs. 1c and 3 ), including to unprecedented heat (Fig. 4 ), through reducing geographical movement of the temperature and temperature–precipitation niches (Extended Data Fig. 9 ). Following Climate Action Tracker’s November 2021 projections 1 , different levels of policy ambition result in ~0.3 °C changes in end-of-century global warming as follows: current policies lead to ~2.7 (2.0–3.6) °C; meeting current 2030 nationally determined contributions (without long-term pledges) leads to ~2.4 (1.9–3.0) °C; additional full implementation of submitted and binding long-term targets leads to ~2.1 (1.7–2.6) °C; and fully implementing all announced targets leads to ~1.8 (1.5–2.4) °C. Overall, going from ~2.7 °C global warming under current policies to meeting the Paris Agreement 1.5 °C target reduces hot exposure from 22 to 5% (2.1 to 0.4 billion; Fig. 3a ). It reduces population left outside the niche due to temperature change only from 29 to 14% (2.8 to 1.3 billion) and it reduces population left outside the niche by temperature plus demographic changes from 39 to 28% (3.7 to 2.7 billion; Fig. 3b ). Thus, each 0.3 °C decline in end-of-century warming reduces hot exposure by 4.3% or 410 million people, it reduces population left outside the niche due to temperature change only by 3.7% or 350 million people, and population left outside the niche due to temperature and demographic changes by 2.8% or 270 million people.

a , b , Regions exposed to unprecedented heat (MAT ≥29 °C) overlaid on population density (number in a ~100 km 2 grid cell) for a world of 9.5 billion (SSP2, 2070) under 2.7 °C global warming ( a ) and 1.5 °C global warming ( b ).

Country-level exposure

We focus on hot exposure as the simplest and most conservative metric. The population exposed to unprecedented heat (MAT ≥29 °C) worldwide declines ~5-fold if global warming is reduced from ~2.7 °C under current policies to meeting the 1.5 °C target (Fig. 5a and Supplementary Data ). Assuming a future world of 9.5 billion, India has the greatest population exposed under 2.7 °C global warming, >600 million, but this reduces >6-fold to ~90 million at 1.5 °C global warming. Nigeria has the second largest population exposed, >300 million under 2.7 °C global warming, but this reduces >7-fold to <40 million at 1.5 °C global warming. For third-ranked Indonesia, hot exposure reduces >20-fold, from ~100 million under 2.7 °C global warming to <5 million at 1.5 °C global warming. For fourth- and fifth-ranked Philippines and Pakistan with >80 million exposed under 2.7 °C global warming, there are even larger proportional reductions at 1.5 °C global warming. Sahelian–Saharan countries including Sudan (sixth ranked) and Niger (seventh) have a ~2-fold reduction in exposure, because they still have a large fraction of land area hot exposed at 1.5 °C global warming (Fig. 5b ). The fraction of land area exposed approaches 100% for several countries under 2.7 °C global warming (Fig. 5b ). Brazil has the greatest absolute land area exposed under 2.7 °C global warming, despite almost no area being exposed at 1.5 °C, and Australia and India also experience massive increases in absolute area exposed (Fig. 4 ). (If the future population reaches 11.1 billion, the ranking of countries by population exposed remains similar, although the numbers exposed increase.) Those most exposed under 2.7 °C global warming come from nations that today are above the median poverty rate and below the median per capita emissions (Fig. 6 ).

a , Population exposed for the top 50 countries ranked under 2.7 °C global warming (dark blue) with exposure at 1.5 °C global warming overlaid (pale blue). Note the break in the x axis for the top two countries. b , Fraction of land area exposed for the top 50 countries (again ranked under 2.7 °C global warming with results for 1.5 °C global warming overlaid). The inset in a summarizes the total global exposure of countries, population and land area at the two levels of global warming, with results for all countries provided in Supplementary Data . UAE, United Arab Emirates; Neth. Antilles, Netherlands Antilles; Brit. Indian Ocean Terr., British Indian Ocean Territory.

Solid lines show the median (50% quantile) and dashed lines show the 25% and 75% quantiles for emissions and heat exposure. Points are coloured by quartile of the poverty rate distribution, where poverty rate is defined as the percentage of national population below the US$1.90 poverty line. The density plots at the bottom show the distribution of emissions per capita for each poverty rate quartile.

Relating present emissions to future exposure

Above the present level of 1.2 °C global warming, the increase in hot exposure of 13.8% °C −1 for a future world of ~9.5 billion people (cap.; Fig. 3a ), corresponds to 1.31 × 10 9 cap. °C −1 . The established relationship 53 of cumulative emissions (EgC) to transient global warming is ~1.65 (1.0–2.3) °C EgC −1 . Therefore one person will be exposed to unprecedented heat (MAT ≥29 °C) for every ~460 (330–760) tC emitted. Present (2018 data) global mean per capita CO 2 -equivalent (C eq ) emissions 54 (production-based) are 1.8 tC eq cap. −1 yr −1 . Thus, during their lifetimes (72.6 years) ~3.5 global average citizens today (less than the average household of 4.9 people) emit enough carbon to expose one future person to unprecedented heat. Citizens in richer countries generally have higher emissions 54 , for example, the European Union (2.4 tC eq cap. −1 yr −1 ), the USA (5.3 tC eq cap. −1 yr −1 ) and Qatar (18 tC eq cap. −1 yr −1 ; Fig. 6 ), and consumption-based emissions are even higher. Thus, ~2.7 average European Union citizens or ~1.2 average US citizens emit enough carbon in their lifetimes to expose one future person to unprecedented heat, and the average citizen of Qatar emits enough carbon in their lifetime to expose ~2.8 future people to unprecedented heat. Those future people tend to be in nations that today have per capita emissions around the 25% quantile (Fig. 6 ), including the two countries with the greatest population exposed: India (0.73 tC eq cap. −1 yr −1 ) and Nigeria (0.55 tC eq cap. −1 yr −1 ). We estimate that the average future person exposed to unprecedented heat comes from a place where today per capita emissions are approximately half (56%) of the global average (or 52% in a world of 11.1 billion people).

Our estimate that global warming since 1960–1990 has put more than 600 million people outside the temperature niche is consistent with attributable impacts of climate change affecting 85% of the world’s population 55 . Above the present level of ~1.2 °C global warming, exposure to unprecedented average temperatures (MAT ≥29 °C) is predicted to increase markedly (Fig. 3a ), increasing exposure to temperature extremes (Extended Data Fig. 4 ). This is consistent with extreme humid heat having more than doubled in frequency 42 since 1979, associated with labour loss of 148 million full-time equivalent jobs 19 , with exposure in urban areas increasing for 23% of the world’s population 56 from 1983 to 2016 (due also to growing urban heat islands) and the total urban population exposed tripling 56 (due also to demographic change). Both India and Nigeria already show ‘hotspots’ of increased exposure to extreme heat due predominantly to warming 56 , consistent with our prediction that they are at greatest future risk (Fig. 5 ). These and other emerging economies (for example, Indonesia, Pakistan, Thailand) dominate the total population exposed to unprecedented heat in a 2.7 °C warmer world (Fig. 5 ). Their climate policy commitments also play a significant role in determining end-of-century global warming 5 .

The huge numbers of humans exposed outside the climate niche in our future projections warrant critical evaluation. Combined effects of temperature and demographic change are upper estimates. This is because at any given time the method limits absolute population density of the (currently secondary) higher-temperature peak based on absolute population density of the (currently primary) lower-temperature peak. Yet absolute population density is allowed to vary (everywhere) over time. (This is not an issue for the temperature change only or hot exposure estimates.) Nevertheless, a bias of population growth to hot places clearly increases the proportion (as well as the absolute number) of people exposed to harm from high temperatures 57 . Colder places are projected to become more habitable (Extended Data Fig. 9 ) but are not where population growth is concentrated. Nor do we consider exposure to other sources of climate harm there (or elsewhere), including sea-level rise 30 , 31 , increasing climate extremes 58 and permafrost thaw 59 .

Overall, our results illustrate the huge potential human cost and the great inequity of climate change, informing discussions of loss and damage 60 , 61 . The worst-case scenarios of ~3.6 °C or even ~4.4 °C global warming could put half of the world population outside the historical climate niche, posing an existential risk. The ~2.7 °C global warming expected under current policies puts around a third of the world population outside the niche. It exposes almost the entire area of some countries (for example, Burkina Faso, Mali) to unprecedented heat, including some Small Island Developing States (for example, Aruba, Netherlands Antilles; Fig. 5b )—a group with members already facing an existential risk from sea-level rise. The gains from fully implementing all announced policy targets and limiting global warming to ~1.8 °C are considerable, but would still leave nearly 10% of people exposed to unprecedented heat. Meeting the goal of the Paris Agreement to limit global warming to 1.5 °C halves exposure outside the temperature niche relative to current policies and limits those exposed to unprecedented heat to 5% of people. This still leaves several least-developed countries (for example, Sudan, Niger, Burkina Faso, Mali) with large populations exposed (Fig. 5a ), adding adaptation challenges to an existing climate investment trap 62 . Nevertheless, our results show the huge potential for more decisive climate policy to limit the human costs and inequities of climate change.

Reassessing the climate niche

We plot the running mean of population density against MAT, with a step of 1 °C and a bin size of 2 °C, and then apply double-Gaussian fitting to the resulting curve 14 . Our previous work 14 assessed the human temperature niche by quantifying the 2015 population distribution in relation to the 1960–1990 MAT (Extended Data Fig. 1 ; ‘old reference’). Here, we re-assessed the temperature niche, changing the data to the 1980 population distribution (total 4.4 billion) under the 1960–1990 MAT, for greater internal consistency (Fig. 1a and Extended Data Fig. 1 ; ‘1980’). This is important because there has been significant population growth between 1980 and 2015 with a distinct bias to hotter places. The 1980 population distribution data were obtained from the History Database of the Global Environment (HYDE) 3.2 database 63 . The ensemble mean 1960–1990 climate and associated uncertainty (5th/95th percentiles) were calculated from three sources: (1) WorldClim v.1.4 data 64 ; (2) Climate Research Unit Time Series (CRU TS) v.4.05 monthly data 65 , 66 ; and (3) National Aeronautics and Space Administration Global Land Data Assimilation System (NASA GLDAS-2.1) 3-hourly data 67 . The revised temperature niche was compared with existing results for different historical intervals and datasets from ref. 14 (Extended Data Fig. 1 ). A revised temperature–precipitation niche was also calculated from both MAT and MAP, following the methods in ref. 14 , but using the 1980 population distribution with the 1960–1990 mean climate.

Projecting the niche

Hot exposure is calculated (as previously 14 ) for a given climate and population distribution as the percentage of people exposed to MAT ≥29 °C, from a direct spatial comparison of MAT and population distributions (without any smoothing). The MAT ≥29 °C threshold was chosen as only 0.3% of the 1980 population (12 million) experienced such conditions in the 1960–1990 climate. To separate the effects of climate and demographic changes on geographic displacement of the temperature niche (or the temperature–precipitation niche), we consider the following (Extended Data Fig. 3 ): (1) the geographic distribution of the reference niche (‘reference distribution’); (2) projecting the reference niche function to the geographic distribution of present/future climate (‘ideal distribution’); and (3) the geographically projected ‘assumed distribution’ of present/future population with respect to present/future climate conditions. Here, (2) minus (1) gives the effect of climate change only (as previously 14 ), and (3) minus (2) gives the combined effect of climate and demographic change.

We assessed the relationships between MAT and other thermal metrics proposed to better capture thermal tolerance of humans, focusing on the recent interval 2000–2020. The correlations between MAT and annual MMT or mean annual WBT were assessed using linear regression with the ordinary least square method. MMT was calculated from the fifth generation European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) daily data at ~10 km spatial resolution and CRU TS v.4.06 monthly data at 0.5° spatial resolution. Mean annual WBT was calculated from ERA5 using the ‘one-third rule’ approximation based on a weighted average of dry-bulb and dewpoint temperatures 68 (this is reasonable for the annual average but overestimates daily maximum WBT). We used bias-corrected WBT 69 calculated from temperature and relative humidity data following the method of ref. 70 for six Coupled Model Intercomparison Project Phase 6 (CMIP6) models (limited to CNRM-CM6-1, CNRM-ESM2-1, CanESM5, GFDL-ESM4, MIROC-ES2L and MRI-ESM2-0 due to data availability) to derive daily maximum WBT and mean annual WBT. A model ensemble was created by resampling all model outputs to the coarsest model spatial resolution (2.8°; that of CanESM5 and GFDL-ESM4) using a bilinear interpolation method—each pixel in the resampled raster is the result of a weighted average of the nearest pixels in the original raster (this avoids biassing the ensemble towards higher resolution models). To assess the relationships between MAT and heat extremes, we considered the number of days with maximum temperature >40 °C or with WBT >28 °C. We used the ERA5 hourly data to calculate by grid point the average number of days in a year (between 2000 and 2020) with maximum dry-bulb temperature >40 °C. We used the CMIP6 model ensemble daily maximum WBT to calculate by grid point the average number of days per year (between 2000 and 2020) with maximum WBT >28 °C. Running means were calculated with a bin width of 2 °C, a step of 0.5 °C and a minimum bin size of 20 data points.

To calculate changes up to (near) present, we construct an ensemble mean 2000–2020 climate and associated uncertainty (5th/95th percentiles) from five sources: (1) CRU TS v.4.05 monthly data 65 , 66 ; (2) NASA GLDAS-2.1 3-hourly data 67 ; (3) ECMWF ERA5-Land monthly averaged climate reanalysis data 71 ; (4) NASA Famine Early Warning Systems Network Land Data Assimilation System (FLDAS) monthly data 72 , 73 ; and (5) the United States National Centers for Environmental Prediction Climate Forecast System Version 2 (NCEP CFSv2) 6-hourly data 74 . Each climate dataset is aggregated to calculate MAT and precipitation. The 2000–2020 climate represents 1.0 °C global warming relative to the pre-industrial level. The 2010 population distribution data was obtained from the HYDE 3.2 database 63 . We followed the methods described above to calculate exposure.

Future projections

We used projected climate and population distribution under four different SSPs, which combine different demographic 75 and emissions projections under consistent storylines: SSP1-2.6 (sustainability), SSP2-4.5 (middle of the road), SSP3-7.0 (regional rivalry) and SSP5-8.5 (fossil-fuelled development). We focused on 20-year mean climate states for 2020–2040, 2040–2060, 2060–2080 and 2080–2100, and the projected population distribution data of 2030, 2050, 2070 and 2090, to represent average demographic conditions of corresponding time periods (Extended Data Table 1 ). We obtained downscaled CMIP6 climate data available from WorldClim v.2.0 at 0.0833° (~10 km) resolution, which restricts us to up to eight CMIP6 models: BCC-CSM2-MR, CNRM-CM6-1, CNRM-ESM2-1, CanESM5, GFDL-ESM4, IPSL-CM6A-LR, MIROC-ES2L and MRI-ESM2-0 (Supplementary Table 1 ). We obtained SSP population projection data at 1 km resolution from the spatial population scenarios dataset 76 , 77 . The SSP population projections were derived at national level using methods of multi-dimensional mathematical demography 75 . Alternative assumptions on future fertility, mortality, migration and educational transitions align to the SSP storylines on future development 78 (and exclude climate-induced migration). Spatially explicit data in line with those country-level projections were derived at 1/8° resolution using a parameterized gravity-based downscaling model 76 , and further downscaled to 1 km resolution 77 . We aggregated this population data to a consistent resolution of 0.0833° (~10 km) to match the climate data and our previous analyses. We combine results across climate models to create a multi-model ensemble mean, and a 5–95% confidence interval, recognizing that the number of models available varies somewhat between SSPs and time-slices (Supplementary Table 1 ). To this end, we apply the MAT data of each climate model to plot population density against MAT and then combine the resulting curves to calculate the mean, and 5th and 95th percentiles.

To control for demography and thus isolate the effects of climate policy and associated climate change on exposure, we consider three different fixed populations and their spatial distributions: (1) 6.9 billion as in 2010; (2) 9.5 billion following SSP2 in 2070 75 , 76 , 77 ; and (3) 11.1 billion following SSP3 in 2070 75 , 76 , 77 . These are combined with the observed (2000–2020) 1.0 °C global warming and with different future levels of global warming (1.5, 1.8, 2.0, 2.1, 2.4, 2.7, 3.6 and 4.4 °C) corresponding to different 20-year climate averages from different SSPs (Figs. 1c and 3 , and Extended Data Fig. 7 ). Global warming of 1.5 °C and 2.0 °C are considered because of their relevance to the Paris Agreement. Values of 1.8, 2.1, 2.4 and 2.7 °C are chosen as best estimates of end-of-century global warming corresponding to different policy assumptions, taken from the Climate Action Tracker 1 , which uses an ensemble of runs of the MAGICC6 model that, in turn, emulates different general circulation models from CMIP6. Global warming values of 3.6 and 4.4 °C are chosen as worst-case scenarios that also enable examining the shape of relationships between global warming and population exposure. Twenty-year SSP intervals corresponding to these different levels of global warming are chosen based on mean global warming levels from the CMIP6 model ensemble given in Table SPM.1 of the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change 79 (IPCC). We try to match to warming in 2081–2100, but where earlier time intervals must be used this should have little effect on the results because the spatial pattern of temperature change is highly conserved on the century timescale. The different combinations are: 1.5 °C = SSP1-2.6 in 2021–2040; 1.8 °C = SSP1-2.6 in 2081–2100; 2.0 °C = SSP2-4.5 in 2041–2060; 2.1 °C = SSP3-7.0 in 2041–2060; 2.4 °C = SSP5-8.5 in 2041–2060; 2.7 °C = SSP2-4.5 in 2081–2100; 3.6 °C = SSP3-7.0 in 2081–2100; and 4.4 °C = SSP5-8.5 in 2081–2100. For the same time interval and SSP, different CMIP6 models can give different levels of global warming due to differing climate sensitivity. This is apparent in the spread of population exposure results for individual models (open circles in Fig. 3 ; Extended Data Fig. 8 ). However, we checked that global warming in the multi-model ensemble mean of the CMIP6 models we consider (Supplementary Table 1 ) matches that of the larger CMIP6 ensemble (Table SPM.1 of IPCC AR6).

Country-level estimates

Results for hot exposure for 2.7 °C and 1.5 °C global warming and populations of 9.5 or 11.1 billion were aggregated from the 0.0833° (~10 km) scale of the population and climate data to country scale. This summed the population in all grid cells within a country boundary where MAT ≥29 °C, using geographic information system data for country boundaries from the World Borders Dataset. For the grid cells that are intersected by a country boundary, they were associated with a country if over half the grid cell area fell within the country territory. Results for all countries are given in Supplementary Data .

Emissions and poverty rate of those exposed

Using the country-level breakdown of exposure to unprecedented heat in a 2.7 °C warmer world with 9.5 billion people (Fig. 5a and Supplementary Data ), we calculated a weighted average for number of people exposed multiplied by percentage of global average emissions per capita today. This uses production-based, country-level C eq greenhouse gas emissions from the emissions database for global atmospheric research 54 , for which 2018 is the latest year. The calculation was also done for country-level exposure in a 2.7 °C warmer world of 11.1 billion. Consumption-based emissions (accounting for trade) tend to be lower than production-based emissions in poorer countries and higher in richer countries. This would increase the inequity already apparent in the results. We also examined poverty rate defined as the percentage of population per country below the US$1.90 poverty line, using the interpolated data for 2019 from the World Bank’s Poverty and Inequality Platform 80 . The resulting distribution is heavily skewed with 25% quantile = 0.26%, 50% quantile = 1.79% and 75% quantile = 20%.

Reporting summary

Further information on research design is available in the Nature Portfolio Reporting Summary linked to this article.

Data availability

The historical and current population distribution data are available from the HYDE 3.2 database at https://landuse.sites.uu.nl/datasets/ . The WorldClim v.1.4 data are available at https://doi.org/10.5061/dryad.fj6q573q7 . The CRU TS v.4.05 and v.4.06 monthly data are available at https://crudata.uea.ac.uk/cru/data/hrg/ . The NASA GLDAS-2.1 3-hourly data are available at https://developers.google.com/earth-engine/datasets/catalog/NASA_GLDAS_V021_NOAH_G025_T3H . The ECMWF ERA5 daily data are available at https://developers.google.com/earth-engine/datasets/catalog/ECMWF_ERA5_DAILY . The bias-corrected WBT data are available at https://cds.climate.copernicus.eu/cdsapp#!/dataset/sis-extreme-indices-cmip6 . The ECMWF ERA5-Land monthly data are available at https://developers.google.com/earth-engine/datasets/catalog/ECMWF_ERA5_LAND_MONTHLY . The NASA FLDAS monthly data are available at https://developers.google.com/earth-engine/datasets/catalog/NASA_FLDAS_NOAH01_C_GL_M_V001 . The NCEP CFSv2 6-hourly data are available at https://developers.google.com/earth-engine/datasets/catalog/NOAA_CFSV2_FOR6H . The downscaled CMIP6 climate data are available from WorldClim v.2.0 at https://worldclim.org . The SSP population projection data are available at https://www.cgd.ucar.edu/iam/modeling/spatial-population-scenarios.html . The geographic information system data for country boundaries from the World Borders Dataset are available at https://thematicmapping.org/downloads/world_borders.php . The poverty data for 2019 from the World Bank’s Poverty and Inequality Platform are available at https://pip.worldbank.org/home . All data generated during this study are available from https://doi.org/10.6084/m9.figshare.22650361.v1 .

Code availability

Code used for the analysis is available from https://doi.org/10.6084/m9.figshare.22650760.v1 .

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Acknowledgements

We thank all the data providers. T.M.L., J.F.A. and A.G. are supported by the Open Society Foundations (OR2021-82956). T.M.L. is supported by a Turing Fellowship. C.X. is supported by the National Key R&D Program of China (2022YFF1301000), the National Natural Science Foundation of China (32061143014) and the Fundamental Research Funds for the Central Universities (9610065). J.-C.S. is supported by VILLUM Investigator project ‘Biodiversity Dynamics in a Changing World’ funded by VILLUM FONDEN (grant 16549). M.S. is supported by an ERC Advanced Grant and a Spinoza award. This work is part of the Earth Commission, which is hosted by Future Earth and is the science component of the Global Commons Alliance. The Global Commons Alliance is a sponsored project of Rockefeller Philanthropy Advisors, with support from Oak Foundation, MAVA, Porticus, Gordon and Betty Moore Foundation, Herlin Foundation and the Global Environment Facility.

Author information

These authors contributed equally: Timothy M. Lenton, Chi Xu.

Authors and Affiliations

Global Systems Institute, University of Exeter, Exeter, UK

Timothy M. Lenton, Jesse F. Abrams & Ashish Ghadiali

School of Life Sciences, Nanjing University, Nanjing, China

Potsdam Institute for Climate Impact Research, Potsdam, Germany

Sina Loriani & Boris Sakschewski

International Institute for Applied Systems Analysis, Laxenburg, Austria

Caroline Zimm

Center for Health and the Global Environment, University of Washington, Seattle, WA, USA

Kristie L. Ebi

Department of Applied Ecology, North Carolina State University, Raleigh, NC, USA

Robert R. Dunn

Center for Biodiversity Dynamics in a Changing World (BIOCHANGE) and Section for Ecoinformatics and Biodiversity, Department of Biology, Aarhus University, Aarhus, Denmark

• Jens-Christian Svenning

Wageningen University, Wageningen, The Netherlands

Marten Scheffer

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Contributions

T.M.L., C.X. and M.S. designed the study. C.X. performed the climate niche analyses with input from T.M.L. T.M.L. and J.F.A. related present emissions to future exposure. C.X., J.F.A. and S.L. produced the figures with input from T.M.L., B.S. and C.Z. T.M.L. wrote the paper with input from C.X., J.F.A., A.G., S.L., B.S., C.Z., K.L.E., R.R.D., J.-C.S. and M.S.

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Correspondence to Timothy M. Lenton or Chi Xu .

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Nature Sustainability thanks Enrique Martínez-Meyer and the other, anonymous, reviewers for their contribution to the peer review of this work.

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Extended data

Extended data fig. 1 relative human population density with respect to mean annual temperature (mat)..

Reconstructions from ref. 14 . for a . 300 BP, 500 BP (population data from HYDE database), and b . 6000 BP with population data from ArchaeoGlobe (AG) or HYDE, compared to the 1960-1990 climate (~0.3 °C above pre-industrial) with 2015 population distribution (‘Old reference’, from ref. 14 ) or 1980 population distribution (‘1980’, used here; as in Fig. 1a ), and the smooth fitted functions for the temperature niche used previously 14 (‘Old fitted’) and here (‘1980 fitted’; as in Fig. 1a ) for future projections. Data presented as mean values with the shaded regions corresponding to 5-95 th percentiles. Truncation of the historical reconstructions at higher temperatures is due to excluding bins of data with too few points in them to avoid outlier effects (see ref. 14 ).

Extended Data Fig. 2 Association of the temperature niche minimum with drier climates.

a . The temperature niche has relatively low population density between 19 °C and 24 °C (blue vertical band). Data for 1980 presented as mean values with the shaded regions corresponding to 5-95 th percentiles. b . Frequency distribution of mean annual precipitation (MAP) in the 19-24 °C MAT regions. c . Map of mean annual precipitation with the 19-24 °C MAT regions overlaid (cross hatching) showing they include large areas of deserts.

Extended Data Fig. 3 Workflow for quantifying displacement of the human climate niche due to climate change only or climate and demographic change.

Workflow shown for the temperature niche (but the same approach is used for the temperature-precipitation niche).

Extended Data Fig. 4 Relationships between mean annual temperature (MAT) and accumulated intolerable heat extremes (for 2000-2020).

a . Number of days with maximum temperature above 40 °C calculated using ERA5 data (10 km spatial resolution, n = 2287025). b . Number of days with maximum wet bulb temperature (WBT) above 28 °C calculated using bias corrected data from an ensemble of six CMIP6 models (2.8° spatial resolution, n = 49152). Red curves represent running means (with a bin width of 2 °C and step of 0.5 °C); black vertical lines mark 29 °C MAT. See Methods for further details of models and calculations.

Extended Data Fig. 5 Observed and projected future changes in human population density with respect to Mean Annual Temperature (MAT), following different Shared Socio-economic Pathways (SSPs).

a . SSP1-2.6 leading to ~1.8 °C global warming with a peak of 8.5 billion people. b . SSP3-7.0 scenario leading to ~3.6 °C global warming and 12.1 billion people. c . SSP5-8.5 scenario leading to ~4.4 °C global warming and a peak of 8.6 billion people. (The SSP2-4.5 scenario is shown in Fig. 1b .) For each SSP and 20-year averaged climate interval, global warming and corresponding population levels (for the central year) are summarized in Extended Data Table 1 . Data presented as mean values with the shaded regions corresponding to 5-95 th percentiles.

Extended Data Fig. 6 Population exposed outside of the temperature-precipitation niche, following different Shared Socio-economic Pathways (SSPs).

a, b . Fraction of population (%) left outside of the niche due to: a . climate change only. b . climate and demographic change. c, d . Absolute number left outside of the niche due to: c . climate change only. d . climate and demographic change. Calculations based on mean annual temperature (MAT) and precipitation (MAP) averaged over the 20-year intervals and population density distribution at the centre year of the corresponding intervals. Data presented as mean values with the shaded regions corresponding to 5-95 th percentiles. (Note that the population exposed to unprecedented hot MAT ≥ 29 °C is unaltered by considering precipitation changes).

Extended Data Fig. 7 Changes in human population density with respect to Mean Annual Temperature (MAT) for different fixed population distributions and levels of global warming.

The population distributions are: a . 6.9 billion in 2010, b . 11.1 billion under SSP3 in 2070 (9.5 billion under SSP2 in 2070 is shown in Fig. 1c ). See Methods for the combinations of SSP and 20-year time interval representing different global warming levels. Data presented as mean values with the shaded regions corresponding to 5-95 th percentiles.

Extended Data Fig. 8 Relationships between global warming and temperature-precipitation niche displacement and between global warming and average temperature experienced.

a . Near linear relationship between global warming and temperature-precipitation niche displacement (%) due to temperature and precipitation change only (‘Climate’) and due to climate plus demographic change (‘Combined’). Linear regression results: Climate ( n  = 65, coefficient=14.2 % °C -1 ; forcing intercept at 1960-1990 global warming of 0.3 °C); Combined 6.9 billion ( n  = 65, coefficient=12.0 % °C -1 , r 2  = 0.84); Combined 9.5 billion ( n  = 65, coefficient=10.9 % °C -1 , r 2  = 0.84); Combined 11.1 billion ( n  = 65, coefficient=10.5 % °C -1 , r 2  = 0.84). b . Mean annual temperature felt by an average person for different levels of global warming for fixed population distributions. Linear regression results: 6.9 billion ( n  = 65, coefficient=1.53 °C °C -1 , r 2  = 0.83); 9.5 billion ( n  = 65, coefficient=1.50 °C °C -1 , r 2  = 0.84); 11.1 billion ( n  = 65, coefficient=1.50 °C °C -1 , r 2  = 0.84). The shaded regions correspond to 95% two-sided confidence intervals of the estimated regression coefficients.

Extended Data Fig. 9 Displacement of the temperature and temperature-precipitation niches under different levels of global warming.

a, b . 2.7 °C global warming due to current policies, c, d . 1.5 °C global warming meeting the Paris Agreement. Red indicates a decrease in suitability, green an increase. Note that the less extensive changes in the temperature-precipitation niche are because it already constrains population density more in the driest and wettest regions.

Supplementary information

Supplementary information.

Supplementary Figs. 1 and 2 and Table 1.

Reporting Summary

Supplementary data 1.

Country-level results for population, land area and land fraction exposed to MAT >29 °C.

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Lenton, T.M., Xu, C., Abrams, J.F. et al. Quantifying the human cost of global warming. Nat Sustain 6 , 1237–1247 (2023). https://doi.org/10.1038/s41893-023-01132-6

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The scientific method and climate change: How scientists know

By Holly Shaftel, NASA's Jet Propulsion Laboratory

The scientific method is the gold standard for exploring our natural world. You might have learned about it in grade school, but here’s a quick reminder: It’s the process that scientists use to understand everything from animal behavior to the forces that shape our planet—including climate change.

“The way science works is that I go out and study something, and maybe I collect data or write equations, or I run a big computer program,” said Josh Willis, principal investigator of NASA’s Oceans Melting Greenland (OMG) mission and oceanographer at NASA’s Jet Propulsion Laboratory. “And I use it to learn something about how the world works.”

Using the scientific method, scientists have shown that humans are extremely likely the dominant cause of today’s climate change. The story goes back to the late 1800s, but in 1958, for example, Charles Keeling of the Mauna Loa Observatory in Waimea, Hawaii, started taking meticulous measurements of carbon dioxide (CO 2 ) in the atmosphere, showing the first significant evidence of rapidly rising CO 2 levels and producing the Keeling Curve climate scientists know today.

“The way science works is that I go out and study something, and maybe I collect data or write equations, or I run a big computer program, and I use it to learn something about how the world works.”- Josh Willis, NASA oceanographer and Oceans Melting Greenland principal investigator

Since then, thousands of peer-reviewed scientific papers have come to the same conclusion about climate change, telling us that human activities emit greenhouse gases into the atmosphere, raising Earth’s average temperature and bringing a range of consequences to our ecosystems.

“The weight of all of this information taken together points to the single consistent fact that humans and our activity are warming the planet,” Willis said.

The scientific method’s steps

The exact steps of the scientific method can vary by discipline, but since we have only one Earth (and no “test” Earth), climate scientists follow a few general guidelines to better understand carbon dioxide levels, sea level rise, global temperature and more.

• Form a hypothesis (a statement that an experiment can test)
• Make observations (conduct experiments and gather data)
• Analyze and interpret the data
• Draw conclusions
• Publish results that can be validated with further experiments (rinse and repeat)

As you can see, the scientific method is iterative (repetitive), meaning that climate scientists are constantly making new discoveries about the world based on the building blocks of scientific knowledge.

“The weight of all of this information taken together points to the single consistent fact that humans and our activity are warming the planet." - Josh Willis, NASA oceanographer and Oceans Melting Greenland principal investigator

The scientific method at work.

How does the scientific method work in the real world of climate science? Let’s take NASA’s Oceans Melting Greenland (OMG) campaign, a multi-year survey of Greenland’s ice melt that’s paving the way for improved sea level rise estimates, as an example.

• Form a hypothesis OMG hypothesizes that the oceans are playing a major role in Greenland ice loss.
• Make observations Over a five-year period, OMG will survey Greenland by air and ship to collect ocean temperature and salinity (saltiness) data and take ice thinning measurements to help climate scientists better understand how the ice and warming ocean interact with each other. OMG will also collect data on the sea floor’s shape and depth, which determines how much warm water can reach any given glacier.
• Analyze and interpret data As the OMG crew and scientists collect data around 27,000 miles (over 43,000 kilometers) of Greenland coastline over that five-year period, each year scientists will analyze the data to see how much the oceans warmed or cooled and how the ice changed in response.
• Draw conclusions In one OMG study , scientists discovered that many Greenland glaciers extend deeper (some around 1,000 feet, or about 300 meters) beneath the ocean’s surface than once thought, making them quite vulnerable to the warming ocean. They also discovered that Greenland’s west coast is generally more vulnerable than its east coast.
• Publish results Scientists like Willis write up the results, send in the paper for peer review (a process in which other experts in the field anonymously critique the submission), and then those peers determine whether the information is correct and valuable enough to be published in an academic journal, such as Nature or Earth and Planetary Science Letters . Then it becomes another contribution to the well-substantiated body of climate change knowledge, which evolves and grows stronger as scientists gather and confirm more evidence. Other scientists can take that information further by conducting their own studies to better understand sea level rise.

All in all, the scientific method is “a way of going from observations to answers,” NASA terrestrial ecosystem scientist Erika Podest, based at JPL, said. It adds clarity to our way of thinking and shows that scientific knowledge is always evolving.

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• In Response to Climate Change, Citizens in Advanced Economies Are Willing To Alter How They Live and Work

Many doubt success of international efforts to reduce global warming

Table of contents.

• Acknowledgments
• Methodology

This analysis focuses on attitudes toward global climate change around the world. For this report, we conducted nationally representative Pew Research Center surveys of 16,254 adults from March 12 to May 26, 2021, in 16 advanced economies. All surveys were conducted over the phone with adults in Canada, Belgium, France, Germany, Greece, Italy, the Netherlands, Spain, Sweden, the UK, Australia, Japan, New Zealand, Singapore, South Korea and Taiwan.

In the United States, we surveyed 2,596 U.S. adults from Feb. 1 to 7, 2021. Everyone who took part in the U.S. survey is a member of the Center’s American Trends Panel (ATP), an online survey panel that is recruited through national, random sampling of residential addresses. This way nearly all adults have a chance of selection. The survey is weighted to be representative of the U.S. adult population by gender, race, ethnicity, partisan affiliation, education and other categories.

This study was conducted in countries where nationally representative telephone surveys are feasible. Due to the coronavirus outbreak, face-to-face interviewing is not currently possible in many parts of the world.

Here are the questions used for the report, along with responses. See our methodology database for more information about the survey methods outside the U.S. For respondents in the U.S., read more about the ATP’s methodology .

A new Pew Research Center survey in 17 advanced economies spanning North America, Europe and the Asia-Pacific region finds widespread concern about the personal impact of global climate change. Most citizens say they are willing to change how they live and work at least some to combat the effects of global warming, but whether their efforts will make an impact is unclear.

Citizens offer mixed reviews of how their societies have responded to climate change, and many question the efficacy of international efforts to stave off a global environmental crisis.

Conducted this past spring, before the summer season ushered in new wildfires , droughts , floods and stronger-than-usual storms , the study reveals a growing sense of personal threat from climate change among many of the publics polled. In Germany, for instance, the share that is “very concerned” about the personal ramifications of global warming has increased 19 percentage points since 2015 (from 18% to 37%).

In the study, only Japan (-8 points) saw a significant decline in the share of citizens deeply concerned about climate change. In the United States, views did not change significantly since 2015.

Young adults, who have been at the forefront of some of the most prominent climate change protests in recent years, are more concerned than their older counterparts about the personal impact of a warming planet in many publics surveyed. The widest age gap is found in Sweden, where 65% of 18- to 29-year-olds are at least somewhat concerned about the personal impacts of climate change in their lifetime, compared with just 25% of those 65 and older. Sizable age differences are also found in New Zealand, Australia, the U.S., France and Canada.

Public concern about climate change appears alongside a willingness to reduce its effects by taking personal steps. Majorities in each of the advanced economies surveyed say they are willing to make at least some changes in how they live and work to address the threat posed by global warming. And across all 17 publics polled, a median of 34% are willing to consider “a lot of changes” to daily life as a response to climate change.

Generally, those on the left of the political spectrum are more open than those on the right to taking personal steps to help reduce the effects of climate change. This is particularly true in the U.S., where citizens who identify with the ideological left are more than twice as willing as those on the ideological right (94% vs. 45%) to modify how they live and work for this reason. Other countries where those on the left and right are divided over whether to alter their lives and work in response to global warming include Canada, the Netherlands, Australia and Germany.

Beyond individual actions, the study reveals mixed views on the broader, collective response to climate change. In 12 of the 17 publics polled, half or more think their own society has done a good job dealing with global climate change. But only in Singapore (32%), Sweden (14%), Germany (14%), New Zealand (14%) and the United Kingdom (13%) do more than one-in-ten describe such efforts as “very good.” Meanwhile, fewer than half in Japan (49%), Italy (48%), the U.S. (47%), South Korea (46%) and Taiwan (45%) give their society’s climate response favorable marks.

Abroad, the U.S. response to climate change is generally seen as wanting. Among the 16 other advanced economies surveyed, only Singaporeans are slightly positive in their assessment of American efforts (53% say the U.S. is doing a “good job” of addressing climate change). Elsewhere judgments are harsher, with six-in-ten or more across Australia, New Zealand and many of the European publics polled saying the U.S. is doing a “bad job” of dealing with global warming. However, China fares substantially worse in terms of international public opinion: A median of 78% across 17 publics describe China’s handling of climate change as “bad,” including 45% who describe the Chinese response as “very bad.” That compares with a cumulative median of 61% who judge the American response as “bad.”

At the cross-national level, the European Union’s response to climate change is viewed favorably by majorities in each of the advanced economies surveyed, except Germany where opinion is split (49% good job; 47% bad job). However, there is still room for improvement, as only a median of 7% across the publics polled describe the EU’s efforts as “very good.” The United Nations’ actions to address global warming are also generally seen in a favorable light: A median of 56% say the multilateral organization is doing a good job. But again, the reviews are tempered, with just 5% describing the UN’s response to climate change as “very good.”

Publics in the advanced economies surveyed are divided as to whether actions by the international community can successfully reduce the effects of global warming. Overall, a median of 52% lack confidence that a multilateral response will succeed, compared with 46% who remain optimistic that nations can respond to the impact of climate change by working together. Skepticism of multilateral efforts is most pronounced in France (65%), Sweden (61%) and Belgium (60%), while optimism is most robust in South Korea (68%) and Singapore (66%).

These are among the findings of a new Pew Research Center survey, conducted from Feb. 1 to May 26, 2021, among 18,850 adults in 17 advanced economies.

People concerned climate change will harm them during their lifetimes

Many people across 17 advanced economies are concerned that global climate change will harm them personally at some point in their lifetime. A median of 72% express at least some concern that they will be personally harmed by climate change in their lifetimes, compared with medians of 19% and 11% who say they are not too or not at all concerned, respectively. The share who say they are very concerned climate change will harm them personally ranges from 15% in Sweden to 57% in Greece.

Roughly two-thirds of Canadians and six-in-ten Americans are worried climate change will harm them in their lifetimes. Only 12% of Canadians and 17% of Americans are not at all concerned about the personal impact of global climate change.

Publics in Europe express various degrees of concern for potential harm caused by climate change. Three-quarters or more of those in Greece, Spain, Italy, France and Germany say they are concerned that climate change will harm them at some point during their lives. Only in Sweden does less than a majority of adults express concern about climate change harming them. Indeed, 56% of Swedes are not concerned about personal harm related to climate change.

In general, Asia-Pacific publics express more worry about climate change causing them personal harm than not. The shares who express concern range from 64% in Australia to 88% in South Korea. About one-third or more in South Korea, Singapore and Australia say they are very concerned climate change will harm them personally.

The share who are very concerned climate change will harm them personally at some point during their lives has increased significantly since 2015 in nearly every country where trend data is available. In Germany, for example, the share who say they are very concerned has increased 19 percentage points over the past six years. Double-digit changes are also present in the UK (+18 points), Australia (+16), South Korea (+13) and Spain (+10). The only public where concern for the harm from climate change has decreased significantly since 2015 is Japan (-8 points).

While many worry climate change will harm them personally in the future, there is widespread sentiment that climate change is already affecting the world around them. In Pew Research Center surveys conducted in 2019 and 2020, a median of 70% across 20 publics surveyed said climate change is affecting where they live a great deal or some amount. And majorities in most countries included as part of a 26-nation survey in 2018 thought global climate change was a major threat to their own country (the same was true across all 14 countries surveyed in 2020 ).

Those who place themselves on the left of the ideological spectrum are more likely than those who place themselves on the right to be concerned global climate change will harm them personally during their lifetime. This pattern is present across all 14 nations where ideology is measured. In 10 of these 14, though, majorities across the ideological left, center and right are concerned climate change will harm them personally.

The difference is starkest in the U.S.: Liberals are 59 percentage points more likely than conservatives to express concern for this possibility (87% vs. 28%, respectively). However, large ideological differences are also present in Australia (with liberals 41 points more likely to say this), the Netherlands (+35), Canada (+30), Sweden (+30) and New Zealand (+23).

Women are more concerned than men that climate change will harm them personally in many of the publics polled. In Germany, women are 13 points more likely than men to be concerned that climate change will cause them harm (82% vs 69%, respectively). Double-digit differences are also present across several publics, including the U.S., Sweden, the UK, South Korea, Singapore, Taiwan, Australia and the Netherlands.

When this question was first asked in 2015 , women were also more likely to express concern than their male counterparts that climate change will harm them in the U.S., Germany, Canada, Japan, Spain and Australia.

Young people have been at the forefront of past protests seeking government action on climate change. In eight places surveyed, young adults ages 18 to 29 are more likely than those 65 and older to be concerned climate change will harm them during their lifetime. The difference is greatest in Sweden, home of youth climate activist Greta Thunberg . Young Swedes are 40 points more likely than their older counterparts to say they are concerned about harm from climate change. Large age gaps are also present in New Zealand (with younger adults 31 points more likely to say this), Australia (+30) and Singapore (+20). And young Americans, French, Canadians and Brits are also more likely to say that climate change will personally harm them in their lifetimes.

While large majorities across every age group in Greece and South Korea are concerned climate change will harm them personally, those ages 65 and older are more likely to hold this sentiment than those younger than 30.

Many across the world willing to change how they live and work to reduce effects of climate change

Many across the publics surveyed say they are willing to make at least some changes to the way they live and work to reduce the effects of climate change. A median of 80% across 17 publics say they would make at least some changes to their lives to reduce the effects of climate change, compared with a median of 19% who say they would make a few changes or no changes at all. The share willing to make a lot of changes ranges from 8% in Japan to 62% in Greece.

In North America, about three-quarters or more of both Canadians and Americans say they are willing to make changes to reduce the effects of climate change.

Large majorities across each of the European publics surveyed say they are willing to change personal behavior to address climate change, but the share who say they are willing to make a lot of changes varies considerably. About half or more in Greece, Italy and Spain say they would make a lot of changes, while fewer than a third in Belgium, Germany and the Netherlands say the same.

Majorities in each of the Asia-Pacific publics polled say they would make some or a lot of changes to how they live and work to combat the effects of climate change, including more than three-quarters in South Korea, Singapore, Australia and New Zealand. But in Japan, fully 44% say they are willing to make few or no changes to how they live and work to address climate change, the largest share of any public surveyed.

In eight countries surveyed, those ages 18 to 29 are more likely than those 65 and older to say they are willing to make at least some changes to how they live and work to help reduce the effects of climate change. In France, for example, about nine-in-ten of those younger than 30 are willing to make changes in response to climate change, compared with 62% of those 65 and older.

Ideologically, those on the left are more likely than those on the right to express willingness to change their behavior to help reduce the effects of global climate change. The ideological divide is widest in the U.S., where 94% of liberals say they are willing to make at least some changes to how they live and work to help reduce the effects of climate change, compared with 45% of conservatives. Large ideological differences are also present between those on the left and the right in Canada (a difference of 26 percentage points), the Netherlands (25 points), Australia (23 points) and Germany (22 points).

In most publics, those with more education are more likely than those with less education to say they are willing to adjust their lifestyles in response to the impact of climate change. 1 In Belgium, for example, those with a postsecondary degree or higher are 14 points more likely than those with a secondary education or below to say they are willing to make changes to the way they live. Double-digit differences are also present between those with more education and less education in France, Germany, New Zealand, the Netherlands and Australia.

And in most places surveyed, those with a higher-than-median income are more likely than those with a lower income to express willingness to make at least some changes to reduce the effects of climate change. For example, in Belgium, about three-quarters (76%) of those with a higher income say they would make changes to their lives, compared with 66% of those with a lower income.

Many are generally positive about how their society is handling climate change

Respondents give mostly positive responses when asked to reflect on how their own society is handling climate change. Around half or more in most places say they their society is doing at least a somewhat good job, with a median of 56% saying this across the 17 advanced economies.

Roughly two-thirds (64%) of Canadians say their country is doing a good job, while nearly half of Americans say the same.

In most of the European publics surveyed, majorities believe their nation’s climate change response is at least somewhat good. Those in Sweden and the UK are especially optimistic, with around seven-in-ten saying their society is doing a good job dealing with climate change. In Europe, Italians are the most critical of their country’s performance: 20% say their society is doing a very bad job, the largest share among all publics surveyed.

Around eight-in-ten in Singapore and New Zealand say their publics are doing a good job – the highest levels among all societies surveyed. This includes around a third (32%) in Singapore who say they are doing a very good job. Adults in the other Asia-Pacific publics surveyed are more circumspect; about half or fewer say their society is doing a good job.

Political ideology plays a role in how people evaluate their own public’s handling of climate change. For adults in 10 countries, those on the right tend to rate their country’s performance with regard to climate change more positively. The difference is most stark in Australia: 69% of those on the right say Australia is handling climate change well, compared with just 19% of those on the left – a 50-point difference. A striking difference also appears in the U.S., where conservatives are 41 points more likely than liberals to say the U.S. is doing a good job dealing with climate change.

Evaluations are also tied to how people view governing parties. In 10 of 17 publics surveyed, people who see the governing party positively are more likely than those with a negative view of the party to think climate change is being handled well. The opposite is true in the U.S., where only 33% of Democrats and Democratic-leaning independents say the U.S. is handling climate change well, compared with 61% of those who do not support the Democratic Party.

Mixed views on whether action by the international community can reduce the effects of climate change

Only a median of 46% across the publics polled are confident that actions taken by the international community will significantly reduce the effects of climate change. A median of 52% are not confident these actions will reduce the effects of climate change.

Canadians are generally divided on whether international climate action can reduce the impact of climate change. And 54% of Americans are not confident in the international community’s response to the climate crisis.

In Europe, majorities in Germany and the Netherlands express confidence that international climate action can significantly address climate change. However, majorities in France, Sweden, Belgium and Italy are not confident in climate actions taken by the international community.

South Koreans and Singaporeans say they are confident in international climate action, but elsewhere in the Asia-Pacific region, public opinion is either divided or leans toward pessimism about international efforts.

Opinion of international organizations, like the United Nations, is linked to confidence that actions taken by the international community will significantly reduce the effects of global climate change. Those with a favorable view of the UN are more confident that actions taken by the international community will significantly reduce the effects of climate change than those with an unfavorable view of the UN. This difference is largest in the U.S., where 61% with a favorable view of the UN say international action will reduce the effects of climate change, compared with just 22% of those with an unfavorable view of the organization. Double-digit differences are present in every public polled.

Similarly, in every EU member state included in the survey, those with favorable views of the bloc are more likely to have confidence in international efforts to combat climate change than those with unfavorable views.

Little consensus on whether international climate action will harm or benefit domestic economies

Relatively few in the advanced economies surveyed think actions taken by the international community to address climate change, such as the Paris climate agreement, will mostly benefit or harm their own economy. A median of 31% across 17 publics say these actions will be good for their economy, while a median of 24% believe such actions will mostly harm their economy. A median of 39% say actions like the Paris climate agreement will have no economic impact.

In Sweden, about half (51%) feel international climate actions will mostly benefit their economy. On the other hand, only 18% in France say their public will benefit economically from international climate agreements.

In no public do more than a third say international action on climate change will harm their economy. But in the U.S., which pulled out of the Paris climate agreement under former President Donald Trump and has just recently rejoined the accord under President Joe Biden, a third say international climate agreements will harm the economy. (For more on how international publics view Biden’s international policy actions, see “ America’s Image Abroad Rebounds With Transition From Trump to Biden .”)

The more widespread sentiment among those surveyed is that climate actions will have no impact on domestic economies. In eight publics, four-in-ten or more hold this opinion, including half in France. And in two places – Japan and Taiwan – one-in-five or more offer no opinion.

Those on the left of the ideological spectrum are more likely than those on the right to say international action to address climate change – such as the Paris Agreement – will mostly benefit their economies. U.S. respondents are particularly divided by ideology. Roughly half (53%) of liberals feel international actions related to climate change will benefit the U.S. economy, compared with just 12% of conservatives. The next largest difference is in Canada, where those on the left are 24 percentage points more likely than those on the right to think this type of international action will benefit their economy.

Those on the right in many publics are, in turn, more likely than those on the left to think international actions such as the Paris Agreement will mostly harm their economies. Here again, ideological divisions in the U.S. are much larger than those in other publics: 65% of conservatives say international climate change actions will harm the American economy, compared with 12% of liberals who say the same.

In several advanced economies, those who say their current economic situation is good are more likely to say that actions taken by the international community to address climate change will mostly benefit their economies than those who say the economic situation is bad. In Sweden, for example, a majority (55%) of those who say the current economic situation is good also believe international action like the Paris Agreement will benefit the Swedish economy, compared with 31% who are more negative about the state of the economy.

Evaluating the climate change response from the EU, UN, U.S. and China

In addition to reflecting on their own public, respondents were asked to evaluate how four international organizations or countries are handling global climate change. Of the entities asked about, the European Union receives the best ratings, with a median of 63% across the 17 publics surveyed saying the EU is doing a good job handling climate change. A median of 56% say the same for the United Nations. Far fewer believe the U.S. or China – the two leading nations in carbon dioxide emissions – are doing a good job.

EU handling of climate change receives high marks in and outside of Europe

Majorities in all but two of the publics surveyed think the EU is doing a good job addressing climate change. However, this positivity is tempered, with most respondents saying the EU’s effort is somewhat good, but few saying it is very good.

Praise for the bloc’s response to climate change is common among the European countries surveyed. In Spain and Greece, around seven-in-ten say the EU is doing at least a somewhat good job, and about six-in-ten or more in the UK, Italy, Sweden and France agree. The Dutch and Germans have more mixed feelings about how the EU is responding to climate change. Notably, only about one-in-ten say the EU is doing a very bad job handling climate change in every European country surveyed but Sweden, where only 5% say so.

Seven-in-ten Canadians believe the EU is doing a good job dealing with climate change, and 62% in the U.S. express the same view.

The Asia-Pacific publics surveyed report similarly positive attitudes on the EU’s climate plans. Around seven-in-ten Australians and Singaporeans consider the EU’s response to climate change at least somewhat good. About six-in-ten or more in New Zealand, South Korea, Japan and Taiwan echo this sentiment.

Climate change actions by UN seen positively among most surveyed

Majorities in most publics also consider the UN response to climate change to be good. A median of 49% across all publics surveyed say that the UN’s actions are somewhat good, and a median of 5% say the actions are very good.

Canadians evaluate the UN’s performance on climate more positively than Americans do. In Canada, roughly six-in-ten say the multilateral organization is doing at least a somewhat good job handling climate change. About half of those in the U.S. agree with that evaluation, with 43% of Americans saying the UN is doing a bad job of dealing with climate change.

In Europe, majorities in Spain, Sweden, the UK, Greece and Italy approve of how the UN is dealing with climate change. Fewer than half of adults in the Netherlands, France and Belgium agree with this evaluation, and only about a third in Germany say the same.

Singaporeans stand out as the greatest share of adults among those surveyed who see the UN’s handling of climate change as good. This includes 14% who say the UN response is very good, which is at least double the share in all other societies surveyed. Majorities in Australia and New Zealand similarly say that the UN is doing a good job.

Many critical of U.S. approach to climate change

In most publics surveyed, adults who say the U.S. is doing a good job of handling climate change are in the minority. A median of 33% say the U.S. is doing a somewhat good job, and a median of just 3% believe the U.S. is doing a very good job.

About half of Americans say their own country is doing a good job in dealing with global climate change, but six-in-ten Canadians say their southern neighbor is doing a bad job.

Across Europe, most think the U.S. is doing a bad job of addressing climate change, including 75% of Germans and Swedes. And at least a quarter in all European nations surveyed except the UK and Greece say the U.S. is doing a very bad job.

Singaporeans offer the U.S. approach to climate change the most praise in the Asia-Pacific region and across all publics surveyed; around half say they see the U.S. strategy positively. New Zealanders are the most critical in the Asia-Pacific region: Only about a quarter say the U.S. is doing at least a somewhat good job.

Political ideology is linked to evaluations of the U.S. climate strategy. In 12 countries, those on the right of the political spectrum are significantly more likely than those on the left to say the U.S. is doing a good job dealing with global climate change. The difference is greatest in Australia, Canada and Italy.

Few give China positive marks for handling of climate change

The publics surveyed are unenthusiastic about how China is dealing with climate change. A median of 18% across the publics say China is doing a good job, compared with a median of 78% who say the opposite. Notably, a median of 45% say that China is doing a very bad job handling climate change.

Just 18% of Americans and Canadians believe China is doing a good job handling climate change.

Similarly, few in Europe think China is dealing effectively with climate change. In fact, more than four-in-ten in nearly all European countries polled say China is doing a very bad job with regards to climate change. Criticism is less common in Greece, where a third give China positive marks for its climate change action.

Adults in the Asia-Pacific region also generally give China poor ratings for dealing with climate change. South Koreans are exceptionally critical; about two-thirds say China is doing a very bad job, the highest share in all publics surveyed. About four-in-ten or more in New Zealand, Japan and Australia concur. Singaporeans stand out, as half say China is doing a good job, nearly 20 percentage points higher than the next highest public.

In nine countries surveyed, those with less education are more positive toward China’s response to climate change than those with more education. Likewise, those with lower incomes are more inclined to provide positive evaluations of China’s climate change response. Those with less education or lower incomes are also less likely to provide a response in several publics.

CORRECTION (Oct. 13, 2021): In the chart “Publics are divided over the economic impact of international actions to address global climate change,” the “Don’t Know” column has been edited to reflect updated percentages to correct for a data tabulation error. These changes did not affect the report’s substantive findings.

• For the purpose of comparing educational groups across publics, education levels are standardized based on the UN’s International Standard Classification of Education (ISCED). The “less education” category is secondary education or below and the “more education” category is postsecondary or above in Australia, Belgium, Canada, Denmark, France, Germany, Italy, Japan, Netherlands, New Zealand, Singapore, South Korea, Spain, Sweden, Taiwan, UK and U.S. ↩

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Birds shifting more in time than space as they adjust to global warming

climate change, nature & conservation

As North America heats up due to climate change, animals are responding in three primary ways: moving north, heading to higher elevations and making phenological changes — adjusting annual cycles such as when they breed.

A new UCLA study analyzed 27 years of data across 311 land-based species to examine how North American birds have responded simultaneously using all three methods.

Most previous studies have only looked at individual types of responses to climate change. By examining all three primary responses side by side, researchers were able to get a more expansive and accurate picture of how birds — from finches to falcons — are adjusting for climate change.

In general, birds are moving in the same direction: away from the heat. They’re moving north in latitude, up in elevation and starting their breeding seasons sooner, before it gets too hot.

But they’re not adapting far or fast enough to keep pace with climate change. Adjustments made by birds in the study, which was published in Nature Ecology and Evolution, only accounted for one-third of what would be needed to stay on track with the rate of warming.

Most of the changes they did make were phenological, the researchers found. “Of the temperature tracking we’ve observed in birds, 64% is due to phenology tracking alone,” said Monte Neate-Clegg, UCLA ecologist and lead author of the study.

 On average, birds are advancing their breeding dates by an average of 0.08 day, he said, which may simply represent the easiest, most efficient method. To make up for a change of one degree Celsius, they start breeding a day sooner, instead of moving 1,000 kilometers to the north or rising a few hundred meters in elevation — and finding suitable new habitat there.

“This is a response we’ve hypothesized before, particularly for birds from California,” said Morgan Tingley, a UCLA professor of ecology and evolutionary biology and senior author of the study. “But now, for the first time, we can see how animals are using multiple ways simultaneously to adapt to climate change, and shifting the timing of key life events may just be one of the first and easiest options.”

This principle is represented in the study, which found that birds, on average, are moving just a small amount spatially: 1.1 kilometers per year northward and 1.2 meters per year upward.

These averages include a large amount of variation. Species such as the lesser goldfinch are rapidly moving north and breeding earlier while others, like the black phoebe, are counterintuitively shifting south and downward, likely due to urbanization, precipitation changes and habitat availability. Thus, some are tracking temperature changes completely, others partially, and some are even moving in the opposite direction than would be expected.

Understanding how birds adapt is crucial for conservation efforts. The fact that they’re changing the timing of their breeding season suggests that strategies should focus not solely on habitat protection but also consider the timing of ecological events and how individual species are changing.

“In order to best target our conservation efforts, we need to know how species are and are not adapting to ongoing climate change,” Tingley said. “While shifting the timing of nesting may help birds in the short term, if they do not move in the long term, greater conservation efforts are likely to be necessary.”

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