Causes of climate change

{{short description|none}} {{about|the physical causes of current climate change|the study of how climate change affects specific extreme events|Extreme event attribution}} {{pp-semi-indef}} {{Use dmy dates|date=December 2019}} [[File:Physical Drivers of climate change.svg|thumb|upright=1.35|right|Brown bars indicate drivers that increase global warming, and blue bars indicate those that decrease global warming. Future global warming potential for long lived drivers like carbon dioxide emissions is not represented.]] The scientific community has been investigating the '''causes of current climate change''' for decades. After thousands of studies, the scientific consensus is that it is "unequivocal that human influence has warmed the atmosphere, ocean and land since pre-industrial times."<ref name="AR6WG1CH3">{{Cite book |last1=Eyring |first1=Veronika |title={{Harvnb|IPCC AR6 WG1|2021}} |last2=Gillett |first2=Nathan P. |last3=Achutarao |first3=Krishna M. |last4=Barimalala |first4=Rondrotiana |last5=Barreiro Parrillo |first5=Marcelo |last6=Bellouin |first6=Nicolas |year=2021 |chapter=Chapter 3: Human influence on the climate system |ref={{harvid|IPCC AR6 WG1 Ch3|2021}} |display-authors=4 |chapter-url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter_03.pdf}}</ref>{{rp|3}} This consensus is supported by around 200 scientific organizations worldwide.<ref name="opr list of scientific organizations">{{citation |date=n.d. |author=OPR |title=Office of Planning and Research (OPR) List of Organizations |url=http://opr.ca.gov/s_listoforganizations.php |publisher=OPR, Office of the Governor, State of California |access-date=30 November 2013 |archive-url=https://web.archive.org/web/20140401120753/http://opr.ca.gov/s_listoforganizations.php |archive-date=1 April 2014 }}. Archived page: The source appears to incorrectly list the Society of Biology (UK) twice.</ref> The scientific principle underlying current climate change is the greenhouse effect, which provides that greenhouse gases pass sunlight that heats the earth, but trap some of the resulting heat that radiates from the planet's surface. Large amounts of greenhouse gases such as carbon dioxide and methane have been released into the atmosphere through burning of fossil fuels since the industrial revolution. Indirect emissions from land use change, emissions of other greenhouse gases such as nitrous oxide, and increased concentrations of water vapor in the atmosphere, also contribute to climate change.<ref name="AR6WG1CH3" /> [[File:Global Temperature And Forces With Fahrenheit.svg|thumb|right|Observed temperature vs the 1850–1900 average used by the IPCC as a pre-industrial baseline.<ref>Sources for data and graphic: * Annual global mean surface temperature data from: {{cite web |title=Global temperature / Get the data / Global mean temperature / NOAAGlobalTemp / Download as CSV |url=https://climate.metoffice.cloud/temperature.html |publisher=Met Office (UK) |archive-url=https://web.archive.org/web/20260118194423/https://climate.metoffice.cloud/temperature.html#datasets |archive-date=18 January 2026 |date=2026 |url-status=live}} * Natural driver graphic is at: {{cite web |title=IPCC Sixth Assessment Report / Working Group 1: The Physical Science Basis / Figures: Summary for Policymakers / Figure SPM.1(b) |url=https://www.ipcc.ch/report/ar6/wg1/figures/summary-for-policymakers/ |publisher=Intergovernmental Panel on Climate Change (IPCC) |date=2021 |archive-url=https://web.archive.org/web/20260113075155/https://www.ipcc.ch/report/ar6/wg1/figures/summary-for-policymakers/ |archive-date=13 January 2026 |url-status=live}} Click on "Datasets". * Natural driver dataset is downloadable by clicking on "gmst_changes_model_and_obs.csv" at: {{cite web |title= Summary for Policymakers of the Working Group I Contribution to the IPCC Sixth Assessment Report - data for Figure SPM.1 (v20221116) |url=https://data.ceda.ac.uk/badc/ar6_wg1/data/spm/spm_01/v20221116/panel_b |publisher=Intergovernmental Panel on Climate Change (IPCC) |date=16 November 2022 |archive-url=https://web.archive.org/web/20240216201927/https://data.ceda.ac.uk/badc/ar6_wg1/data/spm/spm_01/v20221116/panel_b |archive-date=16 February 2024 |url-status=live}}</ref><ref name="ipcc pre industrial baseline">{{harvnb|IPCC AR5 SYR Glossary|2014|page=124}}.</ref> The primary driver for increased global temperatures in the industrial era is human activity, with natural forces adding variability.<ref name="USGCRP Chapter 3 Figure 3-1 panel 2">{{harvnb|USGCRP Chapter 3|2017}} [https://science2017.globalchange.gov/chapter/3#fig-3-1 Figure 3.1 panel 2] {{Webarchive|url=https://web.archive.org/web/20180409042234/https://science2017.globalchange.gov/chapter/3/#fig-3-1 |date=9 April 2018 }}, [https://web.archive.org/web/20171103182210/https://science2017.globalchange.gov/chapter/3#fig-3-3 Figure 3.3 panel 5].</ref>]]

The warming from the greenhouse effect has a logarithmic relationship with the concentration of greenhouse gases. This means that every additional fraction of {{CO2}} and the other greenhouse gases ''in the atmosphere'' has a slightly smaller warming effect than the fractions before it as the ''total'' concentration increases. However, only around half of {{CO2}} emissions continually reside in the atmosphere in the first place, as the other half is quickly absorbed by carbon sinks in the land and oceans.<ref name=":0">Bindoff, N.L., W.W.L. Cheung, J.G. Kairo, J. Arístegui, V.A. Guinder, R. Hallberg, N. Hilmi, N. Jiao, M.S. Karim, L. Levin, S. O'Donoghue, S.R. Purca Cuicapusa, B. Rinkevich, T. Suga, A. Tagliabue, and P. Williamson, 2019: [https://www.ipcc.ch/site/assets/uploads/sites/3/2022/03/07_SROCC_Ch05_FINAL.pdf Chapter 5: Changing Ocean, Marine Ecosystems, and Dependent Communities]. In: [https://www.ipcc.ch/srocc/ 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.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 447–587. <nowiki>https://doi.org/10.1017/9781009157964.007</nowiki>.</ref>{{rp|450}} Further, the warming per unit of greenhouse gases is also affected by feedbacks, such as the changes in water vapor concentrations or Earth's albedo (reflectivity).<ref name="AR6_Glossary">IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf Annex VII: Glossary] [Matthews, J.B.R., V. Möller, R. van Diemen, J.S. Fuglestvedt, V. Masson-Delmotte, C. Méndez, S. Semenov, A. Reisinger (eds.)]. In [https://www.ipcc.ch/report/ar6/wg1/ Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 2215–2256, doi:10.1017/9781009157896.022.</ref>{{rp|2233}}

As the warming from {{CO2}} increases, carbon sinks absorb a smaller fraction of total emissions, while the "fast" climate change feedbacks amplify greenhouse gas warming. Thus, the effects counteract one another, and the warming from each unit of {{CO2}} emitted by humans increases temperature in linear proportion to the total amount of emissions.<ref name="AR6WG1CH5">{{Cite book |last1=Canadell |first1=J. G. |last2=Monteiro |first2=P. M. S. |last3=Costa |first3=M. H. |last4=Cotrim da Cunha |first4=L. |last5=Ishii |first5=M. |last6=Jaccard |first6=S. |last7=Cox |first7=P. M. |last8=Eliseev |first8=A. V. |last9=Henson |first9=S. |last10=Koven |first10=C. |last11=Lohila |first11=A. |last12=Patra |first12=P. K. |last13=Piao |first13=S. |last14=Rogelj |first14=J. |last15=Syampungani |first15=S. |last16=Zaehle |first16=S. |last17=Zickfeld |first17=K. |year=2021 |title={{Harvnb|IPCC AR6 WG1|2021}} |chapter=Global Carbon and Other Biogeochemical Cycles and Feedbacks |ref={{harvid|IPCC AR6 WG1 Ch5|2021}} |chapter-url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter_05.pdf}}</ref>{{rp|746}}{{citation needed|date=January 2025}} Further, some fraction of the greenhouse warming has been "masked" by the human-caused emissions of sulfur dioxide, which forms aerosols that have a cooling effect. However, this masking has been receding in the recent years, due to measures to combat acid rain and air pollution caused by sulfates.<ref name="Quaas2022">{{Cite journal |last1=Quaas |first1=Johannes |last2=Jia |first2=Hailing |last3=Smith |first3=Chris |last4=Albright |first4=Anna Lea |last5=Aas |first5=Wenche |last6=Bellouin |first6=Nicolas |last7=Boucher |first7=Olivier |last8=Doutriaux-Boucher |first8=Marie |last9=Forster |first9=Piers M. |last10=Grosvenor |first10=Daniel |last11=Jenkins |first11=Stuart |last12=Klimont |first12=Zbigniew |last13=Loeb |first13=Norman G. |last14=Ma |first14=Xiaoyan |last15=Naik |first15=Vaishali |last16=Paulot |first16=Fabien |last17=Stier |first17=Philip |last18=Wild |first18=Martin |last19=Myhre |first19=Gunnar |last20=Schulz |first20=Michael |date=21 September 2022 |title=Robust evidence for reversal of the trend in aerosol effective climate forcing |url=https://acp.copernicus.org/articles/22/12221/2022/ |journal=Atmospheric Chemistry and Physics |volume=22 |issue=18 |pages=12221–12239 |language=en |doi=10.5194/acp-22-12221-2022 |s2cid=252446168 |hdl=20.500.11850/572791 |hdl-access=free |doi-access=free |bibcode=2022ACP....2212221Q }}</ref><ref>{{cite journal |last1=Cao |first1=Yang |last2=Zhu |first2=Yannian |last3=Wang |first3=Minghuai |last4=Rosenfeld |first4=Daniel |last5=Liang |first5=Yuan |last6=Liu |first6=Jihu |last7=Liu |first7=Zhoukun |last8=Bai |first8=Heming |date=7 January 2023 | title=Emission Reductions Significantly Reduce the Hemispheric Contrast in Cloud Droplet Number Concentration in Recent Two Decades |journal= Journal of Geophysical Research: Atmospheres| volume=128 |issue=2 |article-number=e2022JD037417 |doi=10.1029/2022JD037417 |doi-access=free |bibcode=2023JGRD..12837417C }}</ref>

== Factors affecting Earth's climate == thumb|A diagram which shows where the extra heat retained on Earth due to the energy imbalance is going.|alt=Infographic A forcing is something that is imposed externally on the climate system. External forcings include natural phenomena such as volcanic eruptions and variations in the sun's output.<ref>Le Treut ''et al.'', [http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch1.html Chapter 1: Historical Overview of Climate Change Science] {{Webarchive|url=https://web.archive.org/web/20111221183427/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch1.html|date=21 December 2011}}, [http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-1-1.html FAQ 1.1, What Factors Determine Earth's Climate?] {{Webarchive|url=https://web.archive.org/web/20110626004451/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-1-1.html|date=26 June 2011}}, in {{Harvnb|IPCC AR4 WG1|2007}}.</ref> Human activities can also impose forcings, for example, through changing the composition of Earth's atmosphere. Radiative forcing is a measure of how various factors alter the energy balance of planet Earth.<ref>Forster ''et al.'', [http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2.html Chapter 2: Changes in Atmospheric Constituents and Radiative Forcing] {{Webarchive|url=https://web.archive.org/web/20111221183528/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2.html|date=21 December 2011}}, [http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-2-1.html FAQ 2.1, How do Human Activities Contribute to Climate Change and How do They Compare with Natural Influences?] {{Webarchive|url=https://web.archive.org/web/20110706022116/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/faq-2-1.html|date=6 July 2011}} in {{Harvnb|IPCC AR4 WG1|2007}}.</ref> A positive radiative forcing will lead towards a warming of the surface and, over time, the climate system. Between the start of the Industrial Revolution in 1750, and the year 2005, the increase in the atmospheric concentration of carbon dioxide (chemical formula: {{CO2}}) led to a positive radiative forcing, averaged over the Earth's surface area, of about 1.66 watts per square metre (abbreviated W m−2).<ref name="ipcc radiative forcing">IPCC, [http://www.ipcc.ch/publications_and_data/ar4/wg1/en/spm.html Summary for Policymakers] {{Webarchive|url=https://web.archive.org/web/20181102182309/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/spm.html|date=2 November 2018}}, [http://www.ipcc.ch/publications_and_data/ar4/wg1/en/spmsspm-human-and.html Human and Natural Drivers of Climate Change] {{Webarchive|url=https://web.archive.org/web/20181102212113/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/spmsspm-human-and.html|date=2 November 2018}}, Figure SPM.2, in {{Harvnb|IPCC AR4 WG1|2007}}.</ref>

Climate feedbacks can either amplify or dampen the response of the climate to a given forcing.<ref name="nrc2008" />{{Rp|7|date=November 2012}} There are many feedback mechanisms in the climate system that can either amplify (a positive feedback) or diminish (a negative feedback) the effects of a change in climate forcing.

The climate system varies in response to changes in external forcings.<ref>{{cite book |last=Committee on the Science of Climate Change, US National Research Council |title=Climate Change Science: An Analysis of Some Key Questions |publisher=National Academies Press |year=2001 |isbn=0-309-07574-2 |location=Washington, D.C., US |page=8 |chapter=2. Natural Climatic Variations |doi=10.17226/10139 |access-date=20 May 2011 |chapter-url=http://www.nap.edu/openbook.php?record_id=10139&page=8 |archive-url=https://web.archive.org/web/20110927120212/http://www.nap.edu/openbook.php?record_id=10139&page=8 |archive-date=27 September 2011 |url-status=live}}</ref> The climate system also has ''internal'' variability both in the presence and absence of external forcings. This internal variability is a result of complex interactions between components within the climate system, such as the coupling between the atmosphere and ocean.<ref>Albritton ''et al.'', [http://www.grida.no/climate/ipcc_tar/wg1/010.htm Technical Summary] {{Webarchive|url=https://web.archive.org/web/20111224074756/http://www.grida.no/climate/ipcc_tar/wg1/010.htm|date=24 December 2011}}, [http://www.grida.no/climate/ipcc_tar/wg1/011.htm#box1 Box 1: What drives changes in climate?] {{Webarchive|url=https://web.archive.org/web/20170119085908/http://www.grida.no/climate/ipcc_tar/wg1/011.htm#box1|date=19 January 2017}}, in {{Harvnb|IPCC TAR WG1|2001}}.</ref> An example of internal variability is the El Niño–Southern Oscillation. <div style="clear:both;" class=></div>

== Human-caused influences == [[File:Greenhouse Effect (2017 NASA data).svg|thumb|Energy flows between space, the atmosphere, and Earth's surface. Rising greenhouse gas levels are contributing to an energy imbalance.]] Factors affecting Earth's climate can be broken down into forcings, feedbacks and internal variations.<ref name="nrc2008">{{cite book |author=US National Research Council |url=http://americasclimatechoices.org/climate_change_2008_final.pdf |title=Understanding and responding to climate change: Highlights of National Academies Reports, 2008 edition |publisher=National Academy of Sciences |year=2008 |location=Washington D.C. |access-date=20 May 2011 |archive-url=https://web.archive.org/web/20111213210836/http://americasclimatechoices.org/climate_change_2008_final.pdf |archive-date=13 December 2011 }}</ref>{{Rp|7|date=November 2012}} Four main lines of evidence support the dominant role of human activities in recent climate change:<ref name="epa endangerment fact sheet">{{cite web |last= |year=2009 |title=EPA's Endangerment Finding Climate Change Facts |url=https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100BVZS.txt |url-status=live |archive-url=https://web.archive.org/web/20171223102430/https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100BVZS.txt |archive-date=23 December 2017 |access-date=22 December 2017 |website=National Service Center for Environmental Publications (NSCEP) |id=Report ID: 430F09086}}</ref> # A physical understanding of the climate system: greenhouse gas concentrations have increased and their warming properties are well-established. # There are historical estimates of past climate changes suggest that the recent changes in global surface temperature are unusual. # Advanced climate models are unable to replicate the observed warming unless human greenhouse gas emissions are included. # Observations of natural forces, such as solar and volcanic activity, show that solar activity cannot explain the observed warming. For example, an increase in solar activity would have warmed the entire atmosphere, yet only the lower atmosphere has warmed.{{sfn|USGCRP|2009|p=20}}

Observations from space show that Earth's energy imbalance—a measure of how much more energy Earth absorbs than it radiates into space—reached values in 2023 that were twice that of the best estimate from the IPCC.<ref name=AGUadvances_20250510>{{cite journal |last1=Mauritsen |first1=Thorsten |last2=Tsushima |first2=Yoko |last3=Meyssignac |first3=Benoit |last4=Loeb |first4=Normal G. |last5=Hakuba |first5=Maria |display-authors=4 |title=Earth's Energy Imbalance More Than Doubled in Recent Decades |journal=AGU Advances |date=10 May 2025 |volume=6 |issue=3 |article-number=e2024AV001636 |doi=10.1029/2024AV001636 |publisher=American Geophysical Union|hdl=21.11116/0000-0011-68B9-8 |hdl-access=free }}</ref>

=== Greenhouse gases === thumb|Warming influence of atmospheric greenhouse gases has nearly doubled since 1979, with carbon dioxide and methane being the dominant drivers.<ref name=NOAA_AGGI_2024>{{cite web |title=The NOAA Annual Greenhouse Gas Index (AGGI) |url=https://gml.noaa.gov/aggi/aggi.html |website=NOAA.gov |publisher=National Oceanic and Atmospheric Administration (NOAA) |archive-url=https://web.archive.org/web/20260116020004/https://gml.noaa.gov/aggi/aggi.html |archive-date=16 January 2026 |date=2026 |url-status=live }}</ref> {{Main|Greenhouse gas|Greenhouse gas emissions|Greenhouse effect}} Greenhouse gases are transparent to sunlight, and thus allow it to pass through the atmosphere to heat the Earth's surface. The Earth radiates it as heat, and greenhouse gases absorb a portion of it. This absorption slows the rate at which heat escapes into space, trapping heat near the Earth's surface and warming it over time.<ref>{{cite web|title=The Causes of Climate Change|author=NASA |url=https://climate.nasa.gov/causes|website=Climate Change: Vital Signs of the Planet|access-date=8 May 2019|archive-url=https://web.archive.org/web/20190508000022/https://climate.nasa.gov/causes/|archive-date=8 May 2019|url-status=live}}</ref> While water vapour and clouds are the biggest contributors to the greenhouse effect, they primarily change as a function of temperature. Therefore, they are considered to be feedbacks that change climate sensitivity. On the other hand, gases such as {{CO2}}, tropospheric ozone,<ref>{{Cite journal |last1=Wang |first1=Bin |last2=Shugart |first2=Herman H |last3=Lerdau |first3=Manuel T |date=2017-08-01 |title=Sensitivity of global greenhouse gas budgets to tropospheric ozone pollution mediated by the biosphere |journal=Environmental Research Letters |volume=12 |issue=8 |page=084001 |doi=10.1088/1748-9326/aa7885 |bibcode=2017ERL....12h4001W |issn=1748-9326 |quote=Ozone acts as a greenhouse gas in the lowest layer of the atmosphere, the troposphere (as opposed to the stratospheric ozone layer)|doi-access=free }}</ref> CFCs and nitrous oxide are added or removed independently from temperature. Hence, they are considered to be external forcings that change global temperatures.<ref>{{Cite journal |last1=Schmidt |first1=Gavin A. |last2=Ruedy |first2=Reto A. |last3=Miller |first3=Ron L. |last4=Lacis |first4=Andy A. |date=2010-10-27 |title=Attribution of the present-day total greenhouse effect |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2010JD014287 |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=115 |issue=D20 |article-number=2010JD014287 |doi=10.1029/2010JD014287 |bibcode=2010JGRD..11520106S |issn=0148-0227|url-access=subscription }}</ref><ref>Walsh, J., D. Wuebbles, K. Hayhoe, J. Kossin, K. Kunkel, G. Stephens, P. Thorne, R. Vose, M. Wehner, J. Willis, D. Anderson, V. Kharin, T. Knutson, F. Landerer, T. Lenton, J. Kennedy, and R. Somerville, 2014: [https://www.researchgate.net/publication/292028114_Appendix_3_Climate_Science_Supplement_Climate_Change_Impacts_in_the_United_States_The_Third_National_Climate_Assessment Appendix 3: Climate Science Supplement. Climate Change Impacts in the United States: The Third National Climate Assessment], J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S. Global Change Research Program, 735-789. doi:10.7930/J0KS6PHH</ref>{{Rp|742|date=November 2012}} [[File:Carbon Dioxide 800kyr.svg|thumb|{{CO2}} concentrations over the last 800,000 years as measured from ice cores<ref>{{Cite journal |last1=Lüthi |first1=Dieter |last2=Le Floch |first2=Martine |last3=Bereiter |first3=Bernhard |last4=Blunier |first4=Thomas |last5=Barnola |first5=Jean-Marc |last6=Siegenthaler |first6=Urs |last7=Raynaud |first7=Dominique |last8=Jouzel |first8=Jean |last9=Fischer |first9=Hubertus |last10=Kawamura |first10=Kenji |last11=Stocker |first11=Thomas F. |date=May 2005 |title=High-resolution carbon dioxide concentration record 650,000–800,000 years before present |journal=Nature |language=en |volume=453 |issue=7193 |pages=379–382 |doi=10.1038/nature06949 |pmid=18480821 |bibcode=2008Natur.453..379L |s2cid=1382081 |issn=0028-0836|doi-access=free }}</ref><ref>{{Cite journal |last1=Fischer |first1=Hubertus |last2=Wahlen |first2=Martin |last3=Smith |first3=Jesse |last4=Mastroianni |first4=Derek |last5=Deck |first5=Bruce |date=12 March 1999 |title=Ice Core Records of Atmospheric CO 2 Around the Last Three Glacial Terminations |url=https://www.science.org/doi/10.1126/science.283.5408.1712 |journal=Science |language=en |volume=283 |issue=5408 |pages=1712–1714 |doi=10.1126/science.283.5408.1712 |pmid=10073931 |bibcode=1999Sci...283.1712F |issn=0036-8075|url-access=subscription }}</ref><ref>{{Cite journal |last1=Indermühle |first1=Andreas |last2=Monnin |first2=Eric |last3=Stauffer |first3=Bernhard |last4=Stocker |first4=Thomas F. |last5=Wahlen |first5=Martin |date=1 March 2000 |title=Atmospheric CO 2 concentration from 60 to 20 kyr BP from the Taylor Dome Ice Core, Antarctica |url=http://doi.wiley.com/10.1029/1999GL010960 |journal=Geophysical Research Letters |language=en |volume=27 |issue=5 |pages=735–738 |doi=10.1029/1999GL010960|bibcode=2000GeoRL..27..735I |s2cid=18942742}}</ref><ref>{{Cite web |last1=Etheridge |first1=D. |last2=Steele |first2=L. |last3=Langenfelds |first3=R. |last4=Francey |first4=R. |last5=Barnola |first5=J.-M. |last6=Morgan |first6=V. |date=1998 |title=Historical CO2 Records from the Law Dome DE08, DE08-2, and DSS Ice Cores |url=https://cdiac.ess-dive.lbl.gov/trends/co2/lawdome.html |access-date=20 November 2022 |website=Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory |agency=U.S. Department of Energy}}</ref> (blue/green) and directly<ref>{{Cite web |last1=Keeling |first1=C. |author-link=Charles David Keeling |last2=Whorf |first2=T. |date=2004 |title=Atmospheric CO2 Records from Sites in the SIO Air Sampling Network |url=https://cdiac.ess-dive.lbl.gov/trends/co2/sio-keel.html |access-date=20 November 2022 |website=Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory |agency=U.S. Department of Energy}}</ref> (black)]] Human activity since the Industrial Revolution (about 1750), mainly extracting and burning fossil fuels (coal, oil, and natural gas), has increased the amount of greenhouse gases in the atmosphere, resulting in a radiative imbalance. Over the past 150 years human activities have released increasing quantities of greenhouse gases into the atmosphere. By 2019, the concentrations of {{CO2}} and methane had increased by about 48% and 160%, respectively, since 1750.<ref>{{Harvnb|WMO|2021|p=8}}.</ref> These {{CO2}} levels are higher than they have been at any time during the last 2 million years. Concentrations of methane are far higher than they were over the last 800,000 years.{{Sfn|IPCC AR6 WG1 Technical Summary|2021|p=TS-35}}

This has led to increases in mean global temperature, or global warming. The likely range of human-induced surface-level air warming by 2010–2019 compared to levels in 1850–1900 is 0.8 °C to 1.3 °C, with a best estimate of 1.07 °C. This is close to the observed overall warming during that time of 0.9 °C to 1.2 °C. Temperature changes during that time were likely only ±0.1 °C due to natural forcings and ±0.2 °C due to variability in the climate.{{r|AR6WG1CH3b |p=3, 443|a=The IPCC in this report uses "likely" to indicate a statement with an assessed probability of 66% to 100%.{{Cite book |ref={{harvid|IPCC AR6 WG1 Summary for Policymakers|2021}} |chapter= Summary for Policymakers |chapter-url= https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM_final.pdf |author=IPCC |author-link=IPCC |year=2021 |title={{Harvnb|IPCC AR6 WG1|2021}} |page= 4 n.4 |isbn= 978-92-9169-158-6}}}}

Global anthropogenic greenhouse gas emissions in 2019 were equivalent to 59 billion tonnes of {{CO2}}. Of these emissions, 75% was {{CO2}}, 18% was methane, 4% was nitrous oxide, and 2% was fluorinated gases.<ref name=":1">IPCC, 2022: [https://www.ipcc.ch/report/ar6/wg3/downloads/report/IPCC_AR6_WGIII_SummaryForPolicymakers.pdf Summary for Policymakers] [P.R. Shukla, J. Skea, A. Reisinger, R. Slade, R. Fradera, M. Pathak, A. Al Khourdajie, M. Belkacemi, R. van Diemen, A. Hasija, G. Lisboa, S. Luz, J. Malley, D. McCollum, S. Some, P. Vyas, (eds.)]. In: [https://www.ipcc.ch/report/ar6/wg3/ Climate Change 2022: Mitigation of Climate Change. Contribution of Working Group III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [P.R. Shukla, J. Skea, R. Slade, A. Al Khourdajie, R. van Diemen, D. McCollum, M. Pathak, S. Some, P. Vyas, R. Fradera, M. Belkacemi, A. Hasija, G. Lisboa, S. Luz, J. Malley, (eds.)]. Cambridge University Press, Cambridge, UK and New York, NY, USA. doi: 10.1017/9781009157926.001.</ref>{{Rp|7|date=November 2012}} {{clear}}

==== Carbon dioxide ==== {{Main|Carbon dioxide in Earth's atmosphere}} [[File:CO2 Emissions by Source.svg|thumb|The Global Carbon Project shows how additions to {{CO2}} have been caused by different sources ramping up one after another.<ref>References for Global Carbon Budget chart updated through 2024: * For ''carbon'' entries: {{cite web |title=Home ›The Data Hub 2025 ›The Latest GCB Data (2025) |url=https://globalcarbonbudget.org/datahub/the-latest-gcb-data-2025/# |publisher=Global Carbon Budget |url-status=live}} Click "Global Carbon Budget v2025" to download Excel xlsx file. Multiply these ''carbon'' entries by 3.664 to arrive at ''carbon dioxide'' figures. Contains land use data only since 1959; see OWID references for complete data: * For ''carbon dioxide'' entries for other industry, flaring, cement, gas, oil, and coal: {{cite web |title=CO₂ emissions by fuel |url=https://ourworldindata.org/emissions-by-fuel |publisher=Our World in Data (OWID) |url-status=live}} Download data from chosen chart, "CO₂ emissions by fuel or industry type, World". * For ''carbon dioxide'' entries for land use: {{cite web |title=Annual CO₂ emissions from land-use change |url=https://ourworldindata.org/grapher/co2-land-use?tab=line&country=~OWID_WRL |publisher=Our World in Data (OWID) |url-status=live}} Select "Line", choose "Download", select "Data", click "Download displayed data". </ref>]] [[File:Mauna Loa CO2 monthly mean concentration.svg|thumb|The Keeling Curve shows the long-term increase of atmospheric carbon dioxide ({{CO2}}) concentrations since 1958.]] {{CO2}} emissions primarily come from burning fossil fuels to provide energy for transport, manufacturing, heating, and electricity.<ref>{{cite web |date=18 September 2020 |last1=Ritchie |first1=Hannah |author1-link=Hannah Ritchie |title=Sector by sector: where do global greenhouse gas emissions come from? |website=Our World in Data |url=https://ourworldindata.org/ghg-emissions-by-sector |access-date=28 October 2020}}</ref> Additional {{CO2}} emissions come from deforestation and industrial processes, which include the {{CO2}} released by the chemical reactions for making cement, steel, aluminum, and fertiliser.<ref>{{harvnb|Olivier|Peters|2019|p=17}}; {{harvnb|Our World in Data, 18 September|2020}}; {{harvnb|EPA|2020|ps=: Greenhouse gas emissions from industry primarily come from burning fossil fuels for energy, as well as greenhouse gas emissions from certain chemical reactions necessary to produce goods from raw materials}}; {{cite web|title=Redox, extraction of iron and transition metals|url=https://www.bbc.co.uk/bitesize/guides/zv7f3k7/revision/2|quote=Hot air (oxygen) reacts with the coke (carbon) to produce carbon dioxide and heat energy to heat up the furnace. Removing impurities: The calcium carbonate in the limestone thermally decomposes to form calcium oxide. calcium carbonate → calcium oxide + carbon dioxide}}; {{harvnb|Kvande|2014|ps=: Carbon dioxide gas is formed at the anode, as the carbon anode is consumed upon reaction of carbon with the oxygen ions from the alumina (Al2O3). Formation of carbon dioxide is unavoidable as long as carbon anodes are used, and it is of great concern because CO2 is a greenhouse gas}}</ref>

{{CO2}} is absorbed and emitted naturally as part of the carbon cycle, through animal and plant respiration, volcanic eruptions, and ocean-atmosphere exchange.<ref name="EPAExplainer">{{cite web |date=28 June 2012 |url=http://www.epa.gov/climatechange/science/causes.html#greenhouseeffect |archive-url=https://web.archive.org/web/20170308003615/https://www.epa.gov/climate-change-science/causes-climate-change |archive-date=8 March 2017 |title=Causes of Climate Change: The Greenhouse Effect causes the atmosphere to retain heat |author=US Environmental Protection Agency (EPA) |publisher=EPA |access-date=1 July 2013}}</ref> Human activities, such as the burning of fossil fuels and changes in land use (see below), release large amounts of carbon to the atmosphere, causing {{CO2}} concentrations in the atmosphere to rise.<ref name="EPAExplainer"/><ref>See also: {{citation |volume=2. Validity of Observed and Measured Data |url=http://www.epa.gov/climatechange/endangerment/comments/volume2.html#1 |title=2.1 Greenhouse Gas Emissions and Concentrations |access-date=1 July 2013 |archive-date=27 August 2016 |archive-url=https://web.archive.org/web/20160827230525/https://www3.epa.gov/climatechange/endangerment/comments/volume2.html#1 }}, in {{harvnb|EPA|2009}}</ref>

The high-accuracy measurements of atmospheric {{CO2}} concentration, initiated by Charles David Keeling in 1958, constitute the master time series documenting the changing composition of the atmosphere.<ref name="le treut 2007 CO2 fingerprint">{{citation |author=Le Treut, H. |chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch1s1-3.html#1-3-1 |chapter=1.3.1 The Human Fingerprint on Greenhouse Gases |title=Historical Overview of Climate Change Science |display-authors=etal |access-date=18 August 2012 |archive-date=29 December 2011 |archive-url=https://web.archive.org/web/20111229060759/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch1s1-3.html#1-3-1 }}, in {{Harvnb|IPCC AR4 WG1|2007}}.</ref> These data, known as the Keeling Curve, have iconic status in climate change science as evidence of the effect of human activities on the chemical composition of the global atmosphere.<ref name="le treut 2007 CO2 fingerprint"/>

Keeling's initial 1958 measurements showed 313 parts per million by volume (ppm). Atmospheric {{CO2}} concentrations, commonly written "ppm", are measured in parts-per-million by volume (ppmv). In May 2019, the concentration of {{CO2}} in the atmosphere reached 415 ppm. The last time when it reached this level was 2.6–5.3 million years ago. Without human intervention, it would be 280 ppm.<ref>{{cite news |last1=Rosane |first1=Olivia |title=CO2 Levels Top 415 PPM for First Time in Human History |url=https://www.ecowatch.com/co2-levels-top-415-ppm-2637007719.html |access-date=14 May 2019 |agency=Ecowatch |date=13 May 2019 |archive-date=14 May 2019 |archive-url=https://web.archive.org/web/20190514143012/https://www.ecowatch.com/co2-levels-top-415-ppm-2637007719.html |url-status=live }}</ref>

In 2022–2024, the concentration of {{CO2}} in the atmosphere increased faster than ever before according to National Oceanic and Atmospheric Administration, as a result of sustained emissions and El Niño conditions.<ref>{{cite web |title=During a year of extremes, carbon dioxide levels surge faster than ever |url=https://www.noaa.gov/news-release/during-year-of-extremes-carbon-dioxide-levels-surge-faster-than-ever |website=Home National Oceanic and Atmospheric Administration |date=6 June 2024 |access-date=2 July 2024}}</ref>

In November, 2025 Global Carbon Budget predicted {{CO2}} emissions from burning coal, oil and gas would be a record 38.1 billion tonnes in 2025, up 1.1 percent from the prior year.<ref>{{Cite press release |date=November 13, 2025 |title=Fossil fuel {{CO2}} emissions hit record high in 2025 |url=https://globalcarbonbudget.org/ |access-date=2025-11-17 |publisher=Global Carbon Budget |language=en}}</ref>

==== Methane and nitrous oxide ==== [[File:The Global Methane Budget 2008–2017.png|thumb|Main sources of global methane emissions (2008–2017) according to the Global Carbon Project<ref name="Saunois_2020">{{cite journal |last1=Saunois |first1=M. |last2=Stavert |first2=A.R. |last3=Poulter |first3=B. |display-authors=etal |date=July 15, 2020 |title=The Global Methane Budget 2000–2017 |url=https://essd.copernicus.org/articles/12/1561/2020/ |journal=Earth System Science Data |language=en |volume=12 |issue=3 |pages=1561–1623 |bibcode=2020ESSD...12.1561S |doi=10.5194/essd-12-1561-2020 |issn=1866-3508 |access-date=28 August 2020 |doi-access=free|hdl=1721.1/124698 |hdl-access=free }}</ref>|right]] Methane emissions come from livestock, manure, rice cultivation, landfills, wastewater, and coal mining, as well as oil and gas extraction.<ref>{{harvnb|EPA|2020}}; {{harvnb|Global Methane Initiative|2020|ps=: Estimated Global Anthropogenic Methane Emissions by Source, 2020: Enteric fermentation (27%), Manure Management (3%), Coal Mining (9%), Municipal Solid Waste (11%), Oil & Gas (24%), Wastewater (7%), Rice Cultivation (7%)}}</ref> Nitrous oxide emissions largely come from the microbial decomposition of fertiliser.<ref>{{harvnb|EPA|2019|ps=: Agricultural activities, such as fertilizer use, are the primary source of N2O emissions}}; {{harvnb|Davidson|2009|ps=: 2.0% of manure nitrogen and 2.5% of fertilizer nitrogen was converted to nitrous oxide between 1860 and 2005; these percentage contributions explain the entire pattern of increasing nitrous oxide concentrations over this period}}</ref>

Methane and to a lesser extent nitrous oxide are also major forcing contributors to the greenhouse effect. The Kyoto Protocol lists these together with hydrofluorocarbon (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6),<ref name="kyoto">{{Cite web |title=The Kyoto Protocol |publisher=UNFCCC |url=http://unfccc.int/resource/docs/convkp/kpeng.html |access-date=9 September 2007 |archive-date=25 August 2009 |archive-url=https://web.archive.org/web/20090825212122/http://unfccc.int/resource/docs/convkp/kpeng.html |url-status=live }}</ref> which are entirely artificial gases, as contributors to radiative forcing. The chart at right attributes anthropogenic greenhouse gas emissions to eight main economic sectors, of which the largest contributors are power stations (many of which burn coal or other fossil fuels), industrial processes, transportation fuels (generally fossil fuels), and agricultural by-products (mainly methane from enteric fermentation and nitrous oxide from fertilizer use).<ref>{{citation |title=7. Projecting the Growth of Greenhouse-Gas Emissions |url=http://www.hm-treasury.gov.uk/d/Chapter_7_Projecting_the_Growth_of_Greenhouse-Gas_Emissions.pdf |pages=171–4 |archive-url=https://web.archive.org/web/20121104032244/http://www.hm-treasury.gov.uk/d/Chapter_7_Projecting_the_Growth_of_Greenhouse-Gas_Emissions.pdf |archive-date=4 November 2012 }}, in [http://webarchive.nationalarchives.gov.uk/20100407172811/http://www.hm-treasury.gov.uk/stern_review_report.htm Stern Review Report on the Economics of Climate Change] (pre-publication edition) (2006)</ref> {{clear}}

=== Aerosols === [[File:Bellouin_2019_aerosol_cloud_interactions.jpg|thumb|Air pollution has substantially increased the presence of aerosols in the atmosphere when compared to the preindustrial background levels. Different types of particles have different effects, but overall, cooling from aerosols formed by sulfur dioxide emissions has the overwhelming impact. However, the complexity of aerosol interactions in atmospheric layers makes the exact strength of cooling very difficult to estimate.<ref name="Bellouin2019">{{Cite journal |last1=Bellouin |first1=N. |last2=Quaas |first2=J. |last3=Gryspeerdt |first3=E. |last4=Kinne |first4=S. |last5=Stier |first5=P. |last6=Watson-Parris |first6=D. |last7=Boucher |first7=O. |last8=Carslaw |first8=K. S. |last9=Christensen |first9=M. |last10=Daniau |first10=A.-L. |last11=Dufresne |first11=J.-L. |last12=Feingold |first12=G. |last13=Fiedler |first13=S. |last14=Forster |first14=P. |last15=Gettelman |first15=A. |last16=Haywood |first16=J. M. |last17=Lohmann |first17=U. |last18=Malavelle |first18=F. |last19=Mauritsen |first19=T. |last20=McCoy |first20= D. T. |last21=Myhre |first21=G. |last22=Mülmenstädt |first22=J. |last23=Neubauer |first23=D. |last24=Possner |first24=A. |last25=Rugenstein |first25=M. |last26=Sato |first26=Y. |last27=Schulz |first27=M. |last28=Schwartz |first28=S. E. |last29=Sourdeval |first29=O. |last30=Storelvmo |first30= T. |last31=Toll |first31=V. |last32=Winker |first32=D. |last33=Stevens |first33=B. |date=1 November 2019 |title=Bounding Global Aerosol Radiative Forcing of Climate Change |journal=Reviews of Geophysics |volume=58 |issue=1 |article-number=e2019RG000660 |doi=10.1029/2019RG000660 |pmid=32734279 |pmc=7384191 }}</ref> ]] Air pollution, in the form of aerosols, affects the climate on a large scale.<ref>{{Cite journal |last=McNeill |first=V. Faye |date=2017 |title=Atmospheric Aerosols: Clouds, Chemistry, and Climate |journal=Annual Review of Chemical and Biomolecular Engineering |language=en |volume=8 |issue=1 |pages=427–444 |doi=10.1146/annurev-chembioeng-060816-101538 |pmid=28415861 |issn=1947-5438|doi-access=free }}</ref><ref>{{Cite journal |last1=Samset |first1=B. H. |last2=Sand |first2=M. |last3=Smith |first3=C. J. |last4=Bauer |first4=S. E. |last5=Forster |first5=P. M. |last6=Fuglestvedt |first6=J. S. |last7=Osprey |first7=S. |last8=Schleussner |first8=C.-F. |date=2018 |title=Climate Impacts From a Removal of Anthropogenic Aerosol Emissions |journal=Geophysical Research Letters |language=en |volume=45 |issue=2 |pages=1020–1029 |doi=10.1002/2017GL076079 |issn=0094-8276 |pmc=7427631 |pmid=32801404|bibcode=2018GeoRL..45.1020S }}</ref> Aerosols scatter and absorb solar radiation. From 1961 to 1990, a gradual reduction in the amount of sunlight reaching the Earth's surface was observed. This phenomenon is popularly known as ''global dimming'',<ref>{{harvnb|IPCC AR5 WG1 Ch2|2013|p=183}}.</ref> and is primarily attributed to sulfate aerosols produced by the combustion of fossil fuels with heavy sulfur concentrations like coal and bunker fuel.<ref name="Quaas2022" /> Smaller contributions come from black carbon, organic carbon from combustion of fossil fuels and biofuels, and from anthropogenic dust.<ref>{{harvnb|He|Wang|Zhou|Wild|2018}}; {{Harvnb|Storelvmo|Phillips|Lohmann|Leirvik|2016}}</ref><ref name="NASA2007">{{cite news |date=15 March 2007 |title=Global 'Sunscreen' Has Likely Thinned, Report NASA Scientists |publisher=NASA |url=http://www.nasa.gov/centers/goddard/news/topstory/2007/aerosol_dimming.html |access-date=13 March 2024 |archive-date=22 December 2018 |archive-url=https://web.archive.org/web/20181222142212/https://www.nasa.gov/centers/goddard/news/topstory/2007/aerosol_dimming.html }}</ref><ref>{{Cite web |date=18 February 2021 |title=Aerosol pollution has caused decades of global dimming |url=https://news.agu.org/press-release/aerosol-pollution-caused-decades-of-global-dimming/ |website=American Geophysical Union |access-date=18 December 2023 |archive-url=https://web.archive.org/web/20230327143716/https://news.agu.org/press-release/aerosol-pollution-caused-decades-of-global-dimming/ |archive-date=27 March 2023 }}</ref><ref>{{Cite journal |title=Double Trouble of Air Pollution by Anthropogenic Dust |year=2022 |doi=10.1021/acs.est.1c04779 |last1=Xia |first1=Wenwen |last2=Wang |first2=Yong |last3=Chen |first3=Siyu |last4=Huang |first4=Jianping |last5=Wang |first5=Bin |last6=Zhang |first6=Guang J. |last7=Zhang |first7=Yue |last8=Liu |first8=Xiaohong |last9=Ma |first9=Jianmin |last10=Gong |first10=Peng |last11=Jiang |first11=Yiquan |last12=Wu |first12=Mingxuan |last13=Xue |first13=Jinkai |last14=Wei |first14=Linyi |last15=Zhang |first15=Tinghan |journal=Environmental Science & Technology |volume=56 |issue=2 |pages=761–769 |pmid=34941248 |bibcode=2022EnST...56..761X |hdl=10138/341962 |s2cid=245445736 |doi-access=free |hdl-access=free }}</ref><ref>{{Cite web |title=Global Dimming Dilemma |date=4 June 2020 |url=https://www.scientistswarning.org/2020/06/04/dimming-dilemma/}}</ref> Globally, aerosols have been declining since 1990 due to pollution controls, meaning that they no longer mask greenhouse gas warming as much.<ref>{{harvnb|Wild|Gilgen|Roesch|Ohmura|2005}}; {{Harvnb|Storelvmo|Phillips|Lohmann|Leirvik|2016}}; {{harvnb|Samset|Sand|Smith|Bauer|2018}}.</ref><ref name="Quaas2022" />

Aerosols also have indirect effects on the Earth's energy budget. Sulfate aerosols act as cloud condensation nuclei and lead to clouds that have more and smaller cloud droplets. These clouds reflect solar radiation more efficiently than clouds with fewer and larger droplets.<ref>{{Cite journal |last=Twomey |first=S. |date=1977 |title=The Influence of Pollution on the Shortwave Albedo of Clouds |journal=Journal of the Atmospheric Sciences |language=en |volume=34 |issue=7 |pages=1149–1152 |doi=10.1175/1520-0469(1977)034<1149:TIOPOT>2.0.CO;2 |bibcode=1977JAtS...34.1149T |issn=0022-4928 |doi-access=free }}{{Dead link|date=March 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> They also reduce the growth of raindrops, which makes clouds more reflective to incoming sunlight.<ref>{{harvnb|Albrecht|1989}}.</ref> Indirect effects of aerosols are the largest uncertainty in radiative forcing.<ref name="NCAR4_ch2">{{cite book |first1=D. W. |last1=Fahey |first2=S. J. |last2=Doherty |first3=K. A. |last3=Hibbard |first4=A. |last4=Romanou |first5=P. C. |last5=Taylor |year=2017 |title=National Climate Assessment |chapter=Chapter 2: Physical Drivers of Climate Change |chapter-url=https://science2017.globalchange.gov/downloads/CSSR_Ch2_Physical_Drivers.pdf |archive-date=11 July 2023 |access-date=13 March 2024 |archive-url=https://archive.today/20230711092029/https://science2017.globalchange.gov/downloads/CSSR_Ch2_Physical_Drivers.pdf }}</ref>

While aerosols typically limit global warming by reflecting sunlight, black carbon in soot that falls on snow or ice can contribute to global warming. Not only does this increase the absorption of sunlight, it also increases melting and sea-level rise.<ref>{{harvnb|Ramanathan|Carmichael|2008}}; {{harvnb|RIVM|2016}}.</ref> Limiting new black carbon deposits in the Arctic could reduce global warming by 0.2 °C by 2050.<ref>{{Cite journal |last1=Sand |first1=M. |last2=Berntsen |first2=T. K. |last3=von Salzen |first3=K. |last4=Flanner |first4=M. G. |last5=Langner |first5=J. |last6=Victor |first6=D. G. |date=2016 |title=Response of Arctic temperature to changes in emissions of short-lived climate forcers |url=https://www.nature.com/articles/nclimate2880 |journal=Nature Climate Change |language=en |volume=6 |issue=3 |pages=286–289 |doi=10.1038/nclimate2880 |bibcode=2016NatCC...6..286S |issn=1758-678X|url-access=subscription }}</ref> {{clear}}

===Land surface changes=== {{Further|Climate change#Land surface changes}} thumb |The rate of global tree cover loss has approximately doubled since 2001, to an annual loss approaching an area the size of Italy.<ref name=WRIforestExtent_thru2025>{{cite web |last1=Weisse |first1=Mikaela |last2=Goldman |first2=Elizabeth |title=Indicators of Forest Extent / Forest Loss / |url=https://gfr.wri.org/forest-extent-indicators/forest-loss |publisher=World Resources Institute (WRI) |archive-url=https://web.archive.org/web/20260430190648/https://gfr.wri.org/forest-extent-indicators/forest-loss |archive-date=30 April 2026 |date=April 2026 |url-status=live}} Chart in section titled "Annual rates of global tree cover loss have risen since 2000".</ref> According to Food and Agriculture Organization, around 30% of Earth's land area is largely unusable for humans (glaciers, deserts, etc.), 26% is forests, 10% is shrubland and 34% is agricultural land.<ref>{{Cite journal |last1=Ritchie |first1=Hannah |last2=Roser |first2=Max |date=2024-02-16 |title=Land Use |url=https://ourworldindata.org/land-use |journal=Our World in Data}}</ref> Deforestation is the main land use change contributor to global warming,<ref>{{harvnb|The Sustainability Consortium, 13 September|2018}}; {{harvnb|UN FAO|2016|p=18}}.</ref> Between 1750 and 2007, about one-third of anthropogenic {{CO2}} emissions were from changes in land use - primarily from the decline in forest area and the growth in agricultural land.<ref>{{citation |author=Solomon, S. |chapter-url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/tssts-2-1-1.html |chapter=TS.2.1.1 Changes in Atmospheric Carbon Dioxide, Methane and Nitrous Oxide |title=Technical Summary |display-authors=etal |access-date=18 August 2012 |archive-date=15 October 2012 |archive-url=https://web.archive.org/web/20121015132903/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/tssts-2-1-1.html }}, in {{Harvnb|IPCC AR4 WG1|2007}}.</ref> primarily deforestation.<ref name="Technical Summary">{{citation |author=Solomon, S. |title=Technical Summary |url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ts.html |display-authors=etal |access-date=25 September 2011 |archive-date=28 November 2018 |archive-url=https://web.archive.org/web/20181128003303/http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ts.html |url-status=live }}, in {{Harvnb|IPCC AR4 WG1|2007}}. {{full citation needed|date=November 2012}}</ref> as the destroyed trees release {{CO2}}, and are not replaced by new trees, removing that carbon sink.<ref name="SRCCL_SPM">{{cite book |title=Special Report on Climate Change and Land |chapter=Summary for Policymakers |chapter-url=https://www.ipcc.ch/site/assets/uploads/sites/4/2019/12/02_Summary-for-Policymakers_SPM.pdf |author=IPCC |author-link=IPCC |year=2019 |pages=3–34}}</ref> Between 2001 and 2018, 27% of deforestation was from permanent clearing to enable agricultural expansion for crops and livestock. Another 24% has been lost to temporary clearing under the shifting cultivation agricultural systems. 26% was due to logging for wood and derived products, and wildfires have accounted for the remaining 23%.<ref>{{Cite journal |last1=Curtis |first1=Philip G. |last2=Slay |first2=Christy M. |last3=Harris |first3=Nancy L. |last4=Tyukavina |first4=Alexandra |last5=Hansen |first5=Matthew C. |date=2018-09-14 |title=Classifying drivers of global forest loss |url=https://www.science.org/doi/10.1126/science.aau3445 |journal=Science |language=en |volume=361 |issue=6407 |pages=1108–1111 |doi=10.1126/science.aau3445 |pmid=30213911 |bibcode=2018Sci...361.1108C |issn=0036-8075|url-access=subscription }}</ref> Some forests have not been fully cleared, but were already degraded by these impacts. Restoring these forests also recovers their potential as a carbon sink.<ref name="Duchelle-2022">{{Cite book |author1=Garrett, L. |author2=Lévite, H. |author3=Besacier, C. |author4=Alekseeva, N. |author5=Duchelle, M. |title=The key role of forest and landscape restoration in climate action |publisher=FAO |year=2022 |isbn=978-92-5-137044-5 |location=Rome|doi=10.4060/cc2510en }}</ref> thumb|upright=1.35|Cumulative land-use change contributions to {{CO2}} emissions, by region.<ref name=":1" />{{Rp|Figure SPM.2b|date=November 2012}} Local vegetation cover impacts how much of the sunlight gets reflected back into space (albedo), and how much heat is lost by evaporation. For instance, the change from a dark forest to grassland makes the surface lighter, causing it to reflect more sunlight. Deforestation can also modify the release of chemical compounds that influence clouds, and by changing wind patterns.<ref name="Seymour 2019">{{harvnb|World Resources Institute, 8 December|2019}}</ref> In tropic and temperate areas the net effect is to produce significant warming, and forest restoration can make local temperatures cooler.<ref name="Duchelle-2022"/> At latitudes closer to the poles, there is a cooling effect as forest is replaced by snow-covered (and more reflective) plains.<ref name="Seymour 2019" /> Globally, these increases in surface albedo have been the dominant direct influence on temperature from land use change. Thus, land use change to date is estimated to have a slight cooling effect.<ref name="IPCC Special Report: Climate change and Land p2-54">{{Harvnb|IPCC SRCCL Ch2|2019|p=172|ps=: "The global biophysical cooling alone has been estimated by a larger range of climate models and is −0.10 ± 0.14 °C; it ranges from −0.57 °C to +0.06°C ... This cooling is essentially dominated by increases in surface albedo: historical land cover changes have generally led to a dominant brightening of land"}}</ref> {{clear}}

====Livestock-associated emissions==== {{See also|Greenhouse gas emissions from agriculture}} thumb|Meat from cattle and sheep have the highest emissions intensity of any agricultural commodity. More than 18% of anthropogenic greenhouse gas emissions are attributed to livestock and livestock-related activities such as deforestation and increasingly fuel-intensive farming practices.<ref name="livestock">{{Cite book |last1=Steinfeld |first1=Henning |url=http://www.virtualcentre.org/en/library/key_pub/longshad/A0701E00.pdf |title=Livestock's Long Shadow |last2=Gerber |first2=Pierre |last3=Wassenaar |first3=Tom |last4=Castel |first4=Vincent |last5=Rosales |first5=Mauricio |last6=de Haan |first6=Cees |publisher=Food and Agricultural Organization of the U.N. |year=2006 |isbn=92-5-105571-8 |url-status=usurped |archive-url=https://web.archive.org/web/20080625012113/http://www.virtualcentre.org/en/library/key_pub/longshad/A0701E00.pdf |archive-date=25 June 2008 }}</ref> Specific attributions to the livestock sector include: * 9% of global anthropogenic carbon dioxide emissions * 35–40% of global anthropogenic methane emissions (chiefly due to enteric fermentation and manure) * 64% of global anthropogenic nitrous oxide emissions, chiefly due to fertilizer use.<ref name="livestock" />

=== Others === Marine plastic pollution reduces the ability of the oceans to absorb CO2 by reducing the photosynthesis of phytoplankton and altering the metabolism in zooplankton. It also creates GHG emissions by creating GHG emitting microbial communities from the decomposition of plastic.<ref>{{cite journal |last1=Nawab |first1=Asim |last2=Tariq Khan |first2=Muhammad |last3=Ihsanullah |first3=I. |last4=Nafees |first4=Mohammad |last5=Mehmood Shah |first5=Aamir |title=From pollution to ocean warming: The climate impacts of marine microplastics |journal=Journal of Hazardous Materials: Plastics |date=23 December 2025 |volume=2 |url=https://www.sciencedirect.com/science/article/pii/S3051060025000320?via%3Dihub#bbib82 |access-date=9 January 2026}}</ref><ref>{{cite web |title=Microplastics Impair Oceans' Carbon Absorption, Worsening Climate Change |url=https://www.azocleantech.com/news.aspx?newsID=36091 |website=AZO Cleantech |access-date=9 January 2026}}</ref> This can even change the oceans from a carbon sink to a carbon source.<ref>{{cite news |last1=Gilliver |first1=Liam |title=How microplastics are chipping away at Earth’s ‘natural shield’ against climate change |url=https://www.euronews.com/green/2026/01/06/how-microplastics-are-chipping-away-at-earths-natural-shield-against-climate-change |access-date=9 January 2026 |agency=Euronews |date=6 January 2026}}</ref> {{clear}}

== Methods for attribution == {{See also|Extreme event attribution}} === "Fingerprint" studies === thumb|Human fingerprints for global warming (summary of observational evidence that human carbon dioxide emissions are causing the climate to warm).<ref>{{Cite web |title=Human Fingerprints |url=https://skepticalscience.com/graphics.php?g=86 |access-date=2024-01-23 |website=Skeptical Science}}</ref> [[File:2017_Global_warming_attribution_-_based_on_NCA4_Fig_3.3.png|thumb|'''Top panel:''' Observed global average temperature change (1870— ).'''Bottom panel:''' Data from the Fourth National Climate Assessment<ref name="4thNCA">{{cite journal |date=2017 |title=Climate Science Special Report: Fourth National Climate Assessment, Volume I - Chapter 3: Detection and Attribution of Climate Change |url=https://science2017.globalchange.gov/chapter/3/ |url-status=live |publisher=U.S. Global Change Research Program (USGCRP) |pages=1–470 |archive-url=https://web.archive.org/web/20190923190450/https://science2017.globalchange.gov/chapter/3/ |archive-date=23 September 2019 |website=science2017.globalchange.gov}} Adapted directly from Fig. 3.3.</ref> is merged for display on the same scale to emphasize relative strengths of forces affecting temperature change. Human-caused forces have increasingly dominated.

]] To determine the human contribution to climate change, unique "fingerprints" for all potential causes are developed and compared with both observed patterns and known internal climate variability.<ref>Knutson, T., 2017: [https://science2017.globalchange.gov/chapter/appendix-c/ Detection and attribution methodologies overview] {{Webarchive|url=https://web.archive.org/web/20240706214341/https://science2017.globalchange.gov/chapter/appendix-c/ |date=6 July 2024 }}. In: ''Climate Science Special Report: Fourth National Climate Assessment, Volume I'' [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, pp. 443-451, doi: 10.7930/J0319T2J</ref><ref>Bindoff, N.L., P.A. Stott, K.M. AchutaRao, M.R. Allen, N. Gillett, D. Gutzler, K. Hansingo, G. Hegerl, Y. Hu, S. Jain, I.I. Mokhov, J. Overland, J. Perlwitz, R. Sebbari and X. Zhang, 2013: [https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapter10_FINAL.pdf Chapter 10: Detection and Attribution of Climate Change: from Global to Regional]. In: [https://www.ipcc.ch/report/ar5/wg1/ Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change] [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.</ref>{{rp|875–876}} For example, solar forcing—whose fingerprint involves warming the entire atmosphere—is ruled out because only the lower atmosphere has warmed.<ref>{{Cite book |url=https://www.globalchange.gov/reports/global-climate-change-impacts-united-states |title=Global climate change impacts in the United States: a state of knowledge report |date=2009 |publisher=Cambridge university press |isbn=978-0-521-14407-0 |location=Cambridge [England] |archive-date=13 December 2012 |access-date=20 March 2024 |archive-url=https://archive.today/20121213094911/http://www.globalchange.gov/publications/reports/scientific-assessments/us-impacts }}</ref>{{rp|20}} Atmospheric aerosols produce a smaller, cooling effect. Other drivers, such as changes in albedo, are less impactful.<ref>IPCC, 2021: [https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_SPM.pdf Summary for Policymakers]. In: [https://www.ipcc.ch/report/ar6/wg1/ Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change] [Masson-Delmotte, V., P. Zhai, A. Pirani, S.L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M.I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J.B.R. Matthews, T.K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, and B. Zhou (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 3−32, doi:10.1017/9781009157896.001.</ref>{{rp|7}}

Fingerprint studies exploit these unique signatures, and allow detailed comparisons of modelled and observed climate change patterns. Scientists rely on such studies to attribute observed changes in climate to a particular cause or set of causes. In the real world, the climate changes that have occurred since the start of the Industrial Revolution are due to a complex mixture of human and natural causes. The importance of each individual influence in this mixture changes over time. Therefore, climate models are used to study how individual factors affect climate. For example, a single factor (like greenhouse gases) or a set of factors can be varied, and the response of the modelled climate system to these individual or combined changes can thus be studied.<ref name=Karlothers2009>{{Harvnb|Karl|others|2009}}, page 19.</ref>

These projections have been confirmed by observations (shown above).<ref name="schneider fingerprint">{{citation |author=Schneider, S. |title=Climate Science |url=http://stephenschneider.stanford.edu/Climate/Climate_Science/Science.html#topofpage |access-date=28 September 2012 |archive-url=https://web.archive.org/web/20130321210328/http://stephenschneider.stanford.edu/Climate/Climate_Science/Science.html#topofpage |archive-date=21 March 2013 |url-status=live |at=[http://stephenschneider.stanford.edu/Climate/Climate_Science/Science.html#Itislikelythathumanactivitieshavecausedadiscernibleimpactonobservedwarmingtrends It is likely that human activities have caused a discernible impact on observed warming trends] |publisher=Stephen H. Schneider, Stanford University}}</ref> For example, when climate model simulations of the last century include all of the major influences on climate, both human-induced and natural, they can reproduce many important features of observed climate change patterns. When human influences are removed from the model experiments, results suggest that the surface of the Earth would actually have cooled slightly over the last 50 years. The clear message from fingerprint studies is that the observed warming over the last half-century cannot be explained by natural factors, and is instead caused primarily by human factors.<ref name=Karlothers2009/>

==== Atmospheric fingerprints ==== Another fingerprint of human effects on climate has been identified by looking at a slice through the layers of the atmosphere, and studying the pattern of temperature changes from the surface up through the stratosphere (see the section on solar activity). The earliest fingerprint work focused on changes in surface and atmospheric temperature. Scientists then applied fingerprint methods to a whole range of climate variables, identifying human-caused climate signals in the heat content of the oceans, the height of the tropopause (the boundary between the troposphere and stratosphere, which has shifted upward by hundreds of feet in recent decades), the geographical patterns of precipitation, drought, surface pressure, and the runoff from major river basins.<ref name=":12">{{Harvnb|Karl|others|2009}}, page 20.</ref>

Studies published after the appearance of the IPCC Fourth Assessment Report in 2007 have also found human fingerprints in the increased levels of atmospheric moisture (both close to the surface and over the full extent of the atmosphere), in the decline of Arctic sea ice extent, and in the patterns of changes in Arctic and Antarctic surface temperatures.<ref name=":12" />

== Ripple effects == ===Carbon sinks === thumb|right|{{CO2}} sources and sinks since 1880. While there is little debate that excess carbon dioxide in the industrial era has mostly come from burning fossil fuels, the future strength of land and ocean carbon sinks is an area of study.<ref>{{cite web |title=CO2 is making Earth greener—for now |date=26 April 2016 |url=https://climate.nasa.gov/news/2436/co2-is-making-earth-greenerfor-now/ |url-status=live |archive-url=https://web.archive.org/web/20200227173022/https://climate.nasa.gov/news/2436/co2-is-making-earth-greenerfor-now/ |archive-date=27 February 2020 |access-date=28 February 2020 |publisher=NASA}}</ref> The Earth's surface absorbs {{CO2}} as part of the carbon cycle. Despite the contribution of deforestation to greenhouse gas emissions, the Earth's land surface, particularly its forests, remain a significant carbon sink for {{CO2}}. Land-surface sink processes, such as carbon fixation in the soil and photosynthesis, remove about 29% of annual global {{CO2}} emissions.<ref>{{Harvnb|IPCC SRCCL Summary for Policymakers|2019|p=10}}</ref> The ocean also serves as a significant carbon sink via a two-step process. First, {{CO2}} dissolves in the surface water. Afterwards, the ocean's overturning circulation distributes it deep into the ocean's interior, where it accumulates over time as part of the carbon cycle. Over the last two decades, the world's oceans have absorbed 20 to 30% of emitted {{CO2}}.<ref name=":0" />{{Rp|450|date=November 2012}} Thus, around half of human-caused {{CO2}} emissions have been absorbed by land plants and by the oceans.<ref>{{harvnb|Climate.gov, 23 June|2022|ps=:"Carbon cycle experts estimate that natural "sinks"—processes that remove carbon from the atmosphere—on land and in the ocean absorbed the equivalent of about half of the carbon dioxide we emitted each year in the 2011–2020 decade."}}</ref>

This fraction of absorbed emissions is not static. If future {{CO2}} emissions decrease, the Earth will be able to absorb up to around 70%. If they increase substantially, it'll still absorb more carbon than now, but the overall fraction will decrease to below 40%.<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=TS-122|loc=Box TS.5, Figure 1}}</ref> This is because climate change increases droughts and heat waves that eventually inhibit plant growth on land, and soils will release more carbon from dead plants when they are warmer.<ref>{{harvnb|Melillo|Frey|DeAngelis|Werner|2017}}: Our first-order estimate of a warming-induced loss of 190 Pg of soil carbon over the 21st century is equivalent to the past two decades of carbon emissions from fossil fuel burning.</ref><ref>{{harvnb|IPCC SRCCL Ch2|2019|pp=133, 144}}.</ref> The rate at which oceans absorb atmospheric carbon will be lowered as they become more acidic and experience changes in thermohaline circulation and phytoplankton distribution.{{sfn|USGCRP Chapter 2|2017|pp=93–95}}<ref name="Liu2022">{{cite journal |last1=Liu |first1=Y. |last2=Moore |first2=J. K. |last3=Primeau |first3=F. |last4=Wang |first4=W. L. |date=22 December 2022 |title=Reduced CO2 uptake and growing nutrient sequestration from slowing overturning circulation |journal=Nature Climate Change |volume=13 |pages=83–90 |doi=10.1038/s41558-022-01555-7 |osti=2242376 |s2cid=255028552 }}</ref><ref name="PearceYale3602023">{{cite web |last=Pearce |first=Fred |date=18 April 2023 |title=New Research Sparks Concerns That Ocean Circulation Will Collapse |url=https://e360.yale.edu/features/climate-change-ocean-circulation-collapse-antarctica |language=en |access-date=3 February 2024 }}</ref>

===Climate change feedbacks === {{Main|Climate change feedback|Climate sensitivity}} [[File:NORTH POLE Ice (19626661335).jpg|thumb|Sea ice reflects 50% to 70% of incoming sunlight, while the ocean, being darker, reflects only 6%. As an area of sea ice melts and exposes more ocean, more heat is absorbed by the ocean, raising temperatures that melt still more ice. This is a positive feedback process.<ref>{{cite web |url=https://nsidc.org/cryosphere/seaice/processes/albedo.html |title=Thermodynamics: Albedo |work=NSIDC |access-date=10 October 2017|archive-url=https://web.archive.org/web/20171011021602/https://nsidc.org/cryosphere/seaice/processes/albedo.html |archive-date=11 October 2017 |url-status=live }}</ref>]]

The response of the climate system to an initial forcing is modified by feedbacks: increased by "self-reinforcing" or "positive" feedbacks and reduced by "balancing" or "negative" feedbacks.<ref>{{cite web |title=The study of Earth as an integrated system |publisher=Earth Science Communications Team at NASA's Jet Propulsion Laboratory / California Institute of Technology |year=2013 |series=Vitals Signs of the Planet |archive-url=https://web.archive.org/web/20190226190002/https://climate.nasa.gov/nasa_science/science/ |archive-date=26 February 2019 |url=https://climate.nasa.gov/nasa_science/science/ |url-status=live}}</ref> The main reinforcing feedbacks are the water-vapour feedback, the ice–albedo feedback, and the net effect of clouds.{{sfn|USGCRP Chapter 2|2017|pp=89–91}}<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=58|ps=: The net effect of changes in clouds in response to global warming is to amplify human-induced warming, that is, the net cloud feedback is positive (high confidence)}}</ref> The primary balancing mechanism is radiative cooling, as Earth's surface gives off more heat to space in response to rising temperature.{{sfn|USGCRP Chapter 2|2017|pp=89–90}} In addition to temperature feedbacks, there are feedbacks in the carbon cycle, such as the fertilizing effect of {{CO2}} on plant growth.<ref>{{harvnb|IPCC AR5 WG1|2013|p=14}}</ref>

Uncertainty over feedbacks, particularly cloud cover,<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|pp=58, 59|ps=: clouds remain the largest contribution to overall uncertainty in climate feedbacks}}</ref> is the major reason why different climate models project different magnitudes of warming for a given amount of emissions.<ref>{{harvnb|Wolff|Shepherd|Shuckburgh|Watson|2015|ps=: "the nature and magnitude of these feedbacks are the principal cause of uncertainty in the response of Earth's climate (over multi-decadal and longer periods) to a particular emissions scenario or greenhouse gas concentration pathway."}}</ref> As air warms, it can hold more moisture. Water vapour, as a potent greenhouse gas, holds heat in the atmosphere.{{sfn|USGCRP Chapter 2|2017|pp=89–91}} If cloud cover increases, more sunlight will be reflected back into space, cooling the planet. If clouds become higher and thinner, they act as an insulator, reflecting heat from below back downwards and warming the planet.<ref>{{Cite journal |last1=Williams |first1=Richard G |last2=Ceppi |first2=Paulo |last3=Katavouta |first3=Anna |date=2020 |title=Controls of the transient climate response to emissions by physical feedbacks, heat uptake and carbon cycling |url=https://iopscience.iop.org/article/10.1088/1748-9326/ab97c9 |journal=Environmental Research Letters |volume=15 |issue=9 |pages=0940c1 |doi=10.1088/1748-9326/ab97c9 |bibcode=2020ERL....15i40c1W |issn=1748-9326|hdl=10044/1/80154 |hdl-access=free }}</ref>

Another major feedback is the reduction of snow cover and sea ice in the Arctic, which reduces the reflectivity of the Earth's surface.<ref>{{harvnb|NASA, 28 May|2013}}.</ref> More of the Sun's energy is now absorbed in these regions, contributing to amplification of Arctic temperature changes.<ref>{{Cite journal |last1=Cohen |first1=Judah |last2=Screen |first2=James A. |last3=Furtado |first3=Jason C. |last4=Barlow |first4=Mathew |last5=Whittleston |first5=David |last6=Coumou |first6=Dim |last7=Francis |first7=Jennifer |last8=Dethloff |first8=Klaus |last9=Entekhabi |first9=Dara |last10=Overland |first10=James |last11=Jones |first11=Justin |date=2014 |title=Recent Arctic amplification and extreme mid-latitude weather |url=https://www.nature.com/articles/ngeo2234 |journal=Nature Geoscience |language=en |volume=7 |issue=9 |pages=627–637 |doi=10.1038/ngeo2234 |bibcode=2014NatGe...7..627C |issn=1752-0894|hdl=10871/20621 |hdl-access=free |url-access=subscription }}</ref> Arctic amplification is also thawing permafrost, which releases methane and {{CO2}} into the atmosphere.<ref name="Turetsky 2019">{{harvnb|Turetsky|Abbott|Jones|Anthony|2019}}</ref> Climate change can also cause methane releases from wetlands, marine systems, and freshwater systems.{{sfn|Dean|Middelburg|Röckmann|Aerts|2018}} Overall, climate feedbacks are expected to become increasingly positive.<ref>{{harvnb|IPCC AR6 WG1 Technical Summary|2021|p=58|ps=: Feedback processes are expected to become more positive overall (more amplifying of global surface temperature changes) on multi-decadal time scales as the spatial pattern of surface warming evolves and global surface temperature increases.}}</ref>

== Natural variability == {{Further|Climate variability and change|Solar activity and climate}} {{See also|History of climate change science#Discredited theories and reconciled apparent discrepancies}} [[File:2017 Global warming attribution - based on NCA4 Fig 3.3 - single-panel version.svg|thumb|right| The Fourth National Climate Assessment ("NCA4", USGCRP, 2017) includes charts illustrating that neither solar nor volcanic activity can explain the observed warming.<ref>{{cite journal |title=Climate Science Special Report: Fourth National Climate Assessment, Volume I - Chapter 3: Detection and Attribution of Climate Change |url=https://science2017.globalchange.gov/chapter/3/ |website=science2017.globalchange.gov |publisher=U.S. Global Change Research Program (USGCRP) |archive-url=https://web.archive.org/web/20190923190450/https://science2017.globalchange.gov/chapter/3/ |archive-date=23 September 2019 |date=2017 |pages=1–470 }} Adapted directly from Fig. 3.3.</ref><ref>{{cite journal |title=Climate Science Special Report / Fourth National Climate Assessment (NCA4), Volume I /Executive Summary / Highlights of the Findings of the U.S. Global Change Research Program Climate Science Special Report |url=https://science2017.globalchange.gov/chapter/executive-summary/ |website=globalchange.gov |publisher=U.S. Global Change Research Program |archive-url=https://web.archive.org/web/20190614150544/https://science2017.globalchange.gov/chapter/executive-summary/ |archive-date=14 June 2019 |date=23 November 2018 |doi=10.7930/J0DJ5CTG |last1=Wuebbles |first1=D.J. |last2=Fahey |first2=D.W. |last3=Hibbard |first3=K.A. |last4=Deangelo |first4=B. |last5=Doherty |first5=S. |last6=Hayhoe |first6=K. |last7=Horton |first7=R. |last8=Kossin |first8=J.P. |last9=Taylor |first9=P.C. |last10=Waple |first10=A.M. |last11=Yohe |first11=C.P. |pages=1–470 |doi-broken-date=20 August 2025 |doi-access=free|url-access=subscription }}</ref>]] Already in 2001, the IPCC Third Assessment Report had found that, "The combined change in radiative forcing of the two major natural factors (solar variation and volcanic aerosols) is estimated to be negative for the past two, and possibly the past four, decades."<ref>IPCC (2001) [https://www.ipcc.ch/site/assets/uploads/2018/07/WG1_TAR_SPM.pdf Summary for Policymakers] - A Report of Working Group I of the Intergovernmental Panel on Climate Change. In: [https://www.ipcc.ch/report/ar3/wg1/ TAR Climate Change 2001: The Scientific Basis]</ref> Solar irradiance has been measured directly by satellites,<ref>{{Harvnb|National Academies|2008|p=6}}</ref> and indirect measurements are available from the early 1600s onwards.<ref name="NCAR4_ch2" /> Yet, since 1880, there has been no upward trend in the amount of the Sun's energy reaching the Earth, in contrast to the warming of the lower atmosphere (the troposphere).<ref>{{cite web|title=Is the Sun causing global warming?|website=Climate Change: Vital Signs of the Planet|date=18 September 2014 |url=https://climate.nasa.gov/faq/14/is-the-sun-causing-global-warming|access-date=10 May 2019|archive-url=https://web.archive.org/web/20190505160051/https://climate.nasa.gov/faq/14/is-the-sun-causing-global-warming/|archive-date=5 May 2019|url-status=live}}</ref> Similarly, volcanic activity has the single largest natural impact (forcing) on temperature, yet it is equivalent to less than 1% of current human-caused CO2 emissions.<ref>{{Cite journal |last1=Fischer |first1=Tobias P. |last2=Aiuppa |first2=Alessandro |date=2020 |title=AGU Centennial Grand Challenge: Volcanoes and Deep Carbon Global CO 2 Emissions From Subaerial Volcanism—Recent Progress and Future Challenges |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GC008690 |journal=Geochemistry, Geophysics, Geosystems |language=en |volume=21 |issue=3 |article-number=e2019GC008690 |doi=10.1029/2019GC008690 |issn=1525-2027|hdl=10447/498846 |hdl-access=free }}</ref> Volcanic activity as a whole has had negligible impacts on global temperature trends since the Industrial Revolution.<ref name="USGCRP Chapter 2 2017 79">{{harvnb|USGCRP Chapter 2|2017|p=79}}</ref>

Between 1750 and 2007, solar radiation may have at most increased by 0.12 W/m2, compared to 1.6 W/m2 for the net anthropogenic forcing.<ref>IPCC, 2007: [https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-spm-1.pdf Summary for Policymakers]. In: [https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-spm-1.pdf Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change] [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.</ref>{{rp|3}} Consequently, the observed rapid rise in global mean temperatures seen after 1985 cannot be ascribed to solar variability."<ref name=":02">{{cite journal |last1=Lockwood |first1=Mike |last2=Lockwood |first2=Claus |year=2007 |title=Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature |url=http://www.pubs.royalsoc.ac.uk/media/proceedings_a/rspa20071880.pdf |journal=Proceedings of the Royal Society A |volume=463 |issue=2086 |pages=2447–2460 |bibcode=2007RSPSA.463.2447L |doi=10.1098/rspa.2007.1880 |s2cid=14580351 |archive-url=https://web.archive.org/web/20070926023811/http://www.pubs.royalsoc.ac.uk/media/proceedings_a/rspa20071880.pdf |archive-date=26 September 2007 |access-date=21 July 2007}}</ref> Further, the upper atmosphere (the stratosphere) would also be warming if the Sun was sending more energy to Earth, but instead, it has been cooling.<ref name="USGCRP-2009">{{Harvnb|USGCRP|2009|p=20}}.</ref> This is consistent with greenhouse gases preventing heat from leaving the Earth's atmosphere.<ref>{{Harvnb|IPCC AR4 WG1 Ch9|2007|pp=702–703}}; {{harvnb|Randel|Shine|Austin|Barnett|2009}}.</ref> Explosive volcanic eruptions can release gases, dust and ash that partially block sunlight and reduce temperatures, or they can send water vapor into the atmosphere, which adds to greenhouse gases and increases temperatures.<ref>{{cite web |url=https://climate.nasa.gov/news/3204/tonga-eruption-blasted-unprecedented-amount-of-water-into-stratosphere/ |title=Tonga eruption blasted unprecedented amount of water into stratosphere |last=Greicius |first=Tony |date=2022-08-02 |website=NASA Global Climate Change |access-date=2024-01-18 |quote=Massive volcanic eruptions like Krakatoa and Mount Pinatubo typically cool Earth's surface by ejecting gases, dust, and ash that reflect sunlight back into space. In contrast, the Tonga volcano didn't inject large amounts of aerosols into the stratosphere, and the huge amounts of water vapor from the eruption may have a small, temporary warming effect, since water vapor traps heat. The effect would dissipate when the extra water vapor cycles out of the stratosphere and would not be enough to noticeably exacerbate climate change effects.}}</ref> Because both water vapor and volcanic material have low persistence in the atmosphere, even the largest eruptions only have an effect for several years.<ref name="USGCRP Chapter 2 2017 79"/>

== See also == {{Portal|Global warming|Energy}} * Climate change adaptation * Climate change denial * Climate change mitigation * Climate resilience

==References== {{reflist}}

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==== IPCC reports ==== {{refbegin}}

=====Fourth Assessment Report=====  * {{cite book |ref={{harvid|IPCC AR4 WG1|2007}} |author=IPCC |author-link=IPCC |year =2007 |title=Climate Change 2007: The Physical Science Basis |series=Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change |display-editors=4 |editor-first1=S. |editor-last1=Solomon |editor-first2=D. |editor-last2=Qin |editor-first3=M. |editor-last3=Manning |editor-first4=Z. |editor-last4=Chen |editor-first5=M. |editor-last5=Marquis |editor-first6=K. B. |editor-last6=Averyt |editor-first7=M. |editor-last7=Tignor |editor-first8=H. L. |editor-last8=Miller |publisher=Cambridge University Press |url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/contents.html |isbn=978-0-521-88009-1 }}

** {{cite book |ref={{harvid|IPCC AR4 WG1 Ch9|2007}} |chapter=Chapter 9: Understanding and Attributing Climate Change |chapter-url=https://archive.ipcc.ch/pdf/assessment-report/ar4/wg1/ar4-wg1-chapter9.pdf |year=2007 |display-authors=4 |first1=G. C. |last1=Hegerl |first2=F. W. |last2=Zwiers |first3=P. |last3=Braconnot |author-link3=Pascale Braconnot |first4=N. P. |last4=Gillett |first5=Y. |last5=Luo |first6=J. A. |last6=Marengo Orsini |first7=N. |last7=Nicholls |first8=J. E. |last8=Penner |first9=P. A. |last9=Stott |title={{Harvnb|IPCC AR4 WG1|2007}} |pages=663–745 }}

=====Fifth Assessment report===== * {{cite book |ref={{harvid|IPCC AR5 WG1|2013}} |author=IPCC |author-link=IPCC |year=2013 |title=Climate Change 2013: The Physical Science Basis |series=Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change |display-editors=4 |editor1-first=T. F. |editor1-last=Stocker |editor2-first=D. |editor2-last=Qin |editor3-first=G.-K. |editor3-last=Plattner |editor4-first=M. |editor4-last=Tignor |editor5-first=S. K. |editor5-last=Allen |editor6-first=J. |editor6-last=Boschung |editor7-first=A. |editor7-last=Nauels |editor8-first=Y. |editor8-last=Xia |editor9-first=V. |editor9-last=Bex |editor10-first=P. M. |editor10-last=Midgley |publisher=Cambridge University Press |place=Cambridge, UK & New York |isbn=978-1-107-05799-9  |url=http://www.climatechange2013.org/images/report/WG1AR5_ALL_FINAL.pdf  }}. [https://www.ipcc.ch/report/ar5/wg1/ AR5 Climate Change 2013: The Physical Science Basis – IPCC] ** {{cite book |ref={{harvid|IPCC AR5 WG1 Ch2|2013}} |chapter=Chapter 2: Observations: Atmosphere and Surface |chapter-url=https://www.ipcc.ch/site/assets/uploads/2017/09/WG1AR5_Chapter02_FINAL.pdf |year=2013 |display-authors=4 |first1=D. L. |last1=Hartmann |first2=A. M. G. |last2=Klein Tank |first3=M. |last3=Rusticucci |first4=L. V. |last4=Alexander |first5=S. |last5=Brönnimann |first6=Y. |last6=Charabi |first7=F. J. |last7=Dentener |first8=E. J. |last8=Dlugokencky |first9=D. R. |last9=Easterling |first10=A. |last10=Kaplan |first11=B. J. |last11=Soden |first12=P. W. |last12=Thorne |first13=M. |last13=Wild |first14=P. M. |last14=Zhai |title={{Harvnb|IPCC AR5 WG1|2013}} |pages=159–254 }} * {{cite book |author=IPCC AR5 SYR |author-link=IPCC |year=2014 |title=Climate Change 2014: Synthesis Report |series=Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change |editor1=The Core Writing Team |editor-first2=R. K. |editor-last2=Pachauri |editor-first3=L. A. |editor-last3=Meyer |publisher=IPCC |place=Geneva, Switzerland |isbn= |url=https://www.ipcc.ch/report/ar5/syr/ }} ** {{cite book |ref={{harvid|IPCC AR5 SYR Glossary|2014}} |chapter=Annex II: Glossary |chapter-url=https://archive.ipcc.ch/pdf/assessment-report/ar5/syr/AR5_SYR_FINAL_Annexes.pdf |year=2014 |author=IPCC |author-link=IPCC |title={{Harvnb|IPCC AR5 SYR|2014}} }}

=====Special Report: Climate change and Land===== * {{cite book |ref={{harvid|IPCC SRCCL|2019}}  |author=IPCC |author-link=IPCC |display-editors=4 |editor-first1=P. R. |editor-last1=Shukla |editor-first2=J. |editor-last2=Skea |editor-first3=E. |editor-last3=Calvo Buendia |editor-first4=V. |editor-last4=Masson-Delmotte |editor-first5=H.-O. |editor-last5=Pörtner |editor-first6=D. |editor-last6=C. Roberts |editor-first7=P. |editor-last7=Zhai |editor-first8=R. |editor-last8=Slade |editor-first9=S. |editor-last9=Connors |editor-first10=R. |editor-last10=van Diemen |editor-first11=M. |editor-last11=Ferrat |editor-first12=E. |editor-last12=Haughey |editor-first13=S. |editor-last13=Luz |editor-first14=S. |editor-last14=Neogi |editor-first15=M. |editor-last15=Pathak |editor-first16=J. |editor-last16=Petzold |editor-first17=J. |editor-last17=Portugal Pereira |editor-first18=P. |editor-last18=Vyas |editor-first19=E. |editor-last19=Huntley |editor-first20=K. |editor-last20=Kissick |editor-first21=M. |editor-last21=Belkacemi |editor-first22=J. |editor-last22=Malley |year=2019 |title=IPCC Special Report on Climate Change, Desertification, Land Degradation, Sustainable Land Management, Food Security, and Greenhouse gas fluxes in Terrestrial Ecosystems |url=https://www.ipcc.ch/site/assets/uploads/2019/11/SRCCL-Full-Report-Compiled-191128.pdf |publisher=In press }}  ** {{cite book |ref={{harvid|IPCC SRCCL Summary for Policymakers|2019}}  |chapter=Summary for Policymakers |chapter-url=https://www.ipcc.ch/site/assets/uploads/sites/4/2019/12/02_Summary-for-Policymakers_SPM.pdf |author=IPCC |author-link=IPCC |year=2019 |title={{Harvnb|IPCC SRCCL|2019}} |pages=3–34 }}  ** {{cite book |ref={{harvid|IPCC SRCCL Ch2|2019}}  |chapter=Chapter 2: Land-Climate Interactions |chapter-url=https://www.ipcc.ch/site/assets/uploads/2019/11/05_Chapter-2.pdf |display-authors=4 |first1=G. |last1=Jia |first2=E. |last2=Shevliakova |first3=P. E. |last3=Artaxo |first4=N. |last4=De Noblet-Ducoudré |first5=R. |last5=Houghton |first6=J. |last6=House |first7=K. |last7=Kitajima |first8=C. |last8=Lennard |first9=A. |last9=Popp |first10=A. |last10=Sirin |first11=R. |last11=Sukumar |first12=L. |last12=Verchot |year=2019 |title={{Harvnb|IPCC SRCCL|2019}} |pages=131–247 }}

=====Sixth Assessment Report===== * {{Cite book |ref= {{harvid|IPCC AR6 WG1|2021}} |author= IPCC |author-link= IPCC |year= 2021 |title= Climate Change 2021: The Physical Science Basis |series= Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |display-editors= 4 |editor1-first=V. |editor1-last=Masson-Delmotte |editor2-first=P. |editor2-last=Zhai |editor3-first=A. |editor3-last=Pirani |editor4-first=S. L. |editor4-last=Connors |editor5-first=C. |editor5-last=Péan |editor6-first=S. |editor6-last=Berger |editor7-first=N. |editor7-last=Caud |editor8-first=Y. |editor8-last=Chen |editor9-first=L. |editor9-last=Goldfarb |editor10-first=M. I. |editor10-last=Gomis |publisher=Cambridge University Press (In Press) |place=Cambridge, United Kingdom and New York, NY, US |isbn= |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf }} ** {{Cite book |ref={{harvid|IPCC AR6 WG1 Technical Summary|2021}} |chapter=Technical Summary |last1=Arias |first1=Paola A. |last2=Bellouin |first2=Nicolas |last3=Coppola |first3=Erika |last4=Jones |first4=Richard G. |last5=Krinner |first5=Gerhard |display-authors=4 |chapter-url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_TS.pdf |year=2021 |title={{Harvnb|IPCC AR6 WG1|2021}} |pages= }}

===Attribution=== *{{Include-USGov | agency=US EPA | source={{citation |year=2009 |title=Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean Air Act. EPA's Response to Public Comments |publisher=US Environmental Protection Agency (EPA) |author=EPA |url=http://www.epa.gov/climatechange/endangerment/#comments |access-date=23 June 2011 |archive-date=14 August 2012 |archive-url=https://web.archive.org/web/20120814230051/http://www.epa.gov/climatechange/endangerment/#comments }}. }}

*{{Include-USGov|agency=US Global Change Research Program (USGCRP)|source={{cite book |ref=CITEREFKarlothers2009 |year=2009 |title=Global Climate Change Impacts in the United States |editor1=Karl, T.R. |editor2=Melillo. J. |editor3=Peterson, T. |editor4=Hassol, S.J. |publisher=Cambridge University Press |isbn=978-0-521-14407-0 |url=https://downloads.globalchange.gov/usimpacts/pdfs/climate-impacts-report.pdf |access-date=23 December 2017 |archive-date=15 November 2019 |archive-url=https://web.archive.org/web/20191115033015/https://downloads.globalchange.gov/usimpacts/pdfs/climate-impacts-report.pdf |url-status=live }}. Public-domain status of this report can be found on p.4 of source}}

==External links== * [https://www.ipcc.ch/ Intergovernmental Panel on Climate Change] * [http://www.metoffice.gov.uk/climate-guide UK Met Office: Climate Guide] * [https://www.noaa.gov/climate NOAA Climate website] – National Oceanic and Atmospheric Administration in the United States

{{DEFAULTSORT:Causes of Climate Change}} Category:Climate change Category:History of climate variability and change Category:Global environmental issues Category:Human impact on the environment Category:Climate change assessment and attribution Category:Environmental impact of the energy industry Category:Climatology