Editing Causes of climate change (section)

=== Greenhouse gases ===
[[File:1979- Radiative forcing - climate change - global warming - EPA NOAA.svg|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_2023>{{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/20241005195609/https://gml.noaa.gov/aggi/aggi.html |archive-date=5 October 2024 |date=2024 |url-status=live }}</ref>]]
{{Main|Greenhouse gas|Greenhouse gas emissions|Greenhouse effect}}
[[Greenhouse gas]]es are transparent to [[sunlight]], and thus allow it to pass through the atmosphere to heat the Earth's surface. The Earth [[Radiative cooling|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 [[feedback]]s 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 |url=https://iopscience.iop.org/article/10.1088/1748-9326/aa7885 |journal=Environmental Research Letters |volume=12 |issue=8 |pages=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> [[Chlorofluorocarbon|CFCs]] and [[nitrous oxide]] are added or removed independently from temperature. Hence, they are considered to be [[Radiative forcing|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 |doi=10.1029/2010JD014287 |bibcode=2010JGRD..11520106S |issn=0148-0227}}</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 (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 (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}}</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]], [[Petroleum|oil]], and [[natural gas]]), has increased the amount of greenhouse gases in the atmosphere, resulting in a [[radiative forcing|radiative imbalance]]. Over the past 150 years human activities have released increasing quantities of greenhouse gases into the [[Earth's atmosphere|atmosphere]]. By 2019, the [[Carbon dioxide in Earth's atmosphere|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. [[Atmospheric methane|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&nbsp;°C to 1.3&nbsp;°C, with a best estimate of 1.07&nbsp;°C. This is close to the observed overall warming during that time of 0.9&nbsp;°C to 1.2&nbsp;°C. Temperature changes during that time were likely only ±0.1&nbsp;°C due to natural forcings and ±0.2&nbsp;°C due to variability in the climate.{{r|AR6WG1CH3b <!--NOTE:This should be the same source defined in the next reference as "AR6WG1CH3" but for some reason, without the "b" appended here, the combination of citation templates acts as though that reference name is being defined twice, rather than defined in the next paragraph and simply invoked here.  I can't figure out how to fix it to get the correct citation information to display.  User:W.stanovsky 9/26/22-->|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 [[Global warming potential|equivalent to]] 59&nbsp;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}} 
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==== Carbon dioxide ====
{{Main|Carbon dioxide in Earth's atmosphere}}
[[File:CO2 Emissions by Source Since 1880.svg|thumb|The [[Global Carbon Project]] shows how additions to {{CO2}} since 1880 have been caused by different sources ramping up one after another.]]
[[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#Energy sources|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 climate change|deforestation]] and [[Industrial processes#Chemical processes by main basic material|industrial processes]], which include the {{CO2}} released by the chemical reactions for [[Cement#Chemistry|making cement]], [[Blast furnace#Process engineering and chemistry|steel]], [[Hall–Héroult process|aluminum]], and [[haber process|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 (Al<sub>2</sub>O<sub>3</sub>). Formation of carbon dioxide is unavoidable as long as carbon anodes are used, and it is of great concern because CO<sub>2</sub> is a greenhouse gas}}</ref>

{{CO2}} is absorbed and emitted naturally as part of the [[carbon cycle]], through animal and plant [[respiratory system|respiration]], [[Volcano|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 |url-status=dead |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 |url-status=live }}, 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 of Earth|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 |url-status=dead}}, 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 ([[Parts-per notation#Mass fraction vs. mole fraction vs. volume fraction|ppm]]). Atmospheric {{CO2}} concentrations, commonly written "ppm", are measured in parts-per-million by volume ([[Parts-per notation#Mass fraction vs. mole fraction vs. volume fraction|ppmv]]). In May 2019, the concentration of {{CO2}} in the atmosphere reached 415&nbsp;ppm. The last time when it reached this level was 2.6–5.3&nbsp;million years ago. Without human intervention, it would be 280&nbsp;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–Southern Oscillation|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 |access-date=2 July 2024}}</ref>
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==== 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 [[enteric fermentation|come from livestock]], manure, [[Environmental impact of rice cultivation|rice cultivation]], landfills, wastewater, and [[coal seam gas|coal mining]], as well as [[fugitive gas emissions|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|Rice Cultivation]] (7%)}}</ref> Nitrous oxide emissions largely come from the microbial decomposition of [[fertilizer|fertiliser]].<ref>{{harvnb|EPA|2019|ps=: Agricultural activities, such as fertilizer use, are the primary source of N<sub>2</sub>O 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), [[Fluorocarbon|perfluorocarbons]] (PFCs), and [[sulfur hexafluoride]] (SF<sub>6</sub>),<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 [[Air pollution|emissions]] to eight main economic sectors, of which the largest contributors are [[power station]]s (many of which burn coal or other [[fossil fuel]]s), industrial processes, transportation [[fuel]]s (generally [[fossil fuel]]s), 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 |url-status=dead |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 |df=dmy-all}}, 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>
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