Atmospheric methane#Removal processes

{{anchor|Methane in Earth.27s atmosphere}}

{{anchor|Methane as a greenhouse gas}}

File:1979- Radiative forcing - climate change - global warming - EPA NOAA.svg) of long-lived greenhouse gases has nearly doubled in 40 years, with carbon dioxide and methane being the dominant drivers of global warming.{{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 }}]]

File:Physical Drivers of climate change.svg (warming influence) of different contributors to climate change through 2019, as reported in the Sixth IPCC assessment report.]] Methane (CH₄) in the Earth's atmosphere is a powerful greenhouse gas with a global warming potential (GWP) 84 times greater than CO₂ over a 20-year time frame.{{cite web |last1=Stocker |display-authors=etal |title=Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change |url=https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_all_final.pdf |website=ipcc.ch |publisher=Cambridge University Press |access-date=19 October 2021}}{{Cite book |title=Climate change 2013 : the physical science basis : Working Group I contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change |editor-last=Stocker |editor-first=Thomas |isbn=978-1-10741-532-4 |location=New York|url={{google books |plainurl=y |id=o4gaBQAAQBAJ}} |oclc=881236891 |page=166}} Methane is not as persistent as CO₂, and tails off to about 28 times greater than CO₂ over a 100-year time frame.

Radiative or climate forcing is the scientific concept used to measure the human impact on the environment in watts per square meter (W/m²).{{cite web |url=http://climate.envsci.rutgers.edu/climdyn2013/IPCC/IPCC_WGI12-RadiativeForcing.pdf |url-access= |title=Climate Change 2013: The Physical Science Basis – Working Group 1 contribution to the IPCC Fifth Assessment Report: Radiative Forcing in the AR5 |last=Drew |first=Shindell |author-link= |year=2013 |department=Department of Environmental Sciences, School of Environmental and Biological Sciences |website=envsci.rutgers.edu |series= |publisher=Rutgers University |agency=Fifth Assessment Report (AR5) |access-date=15 September 2016 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304083735/http://climate.envsci.rutgers.edu/climdyn2013/IPCC/IPCC_WGI12-RadiativeForcing.pdf |url-status=live }} It refers to the "difference between solar irradiance absorbed by the Earth and energy radiated back to space"{{cite web|url=https://earthobservatory.nasa.gov/Features/EnergyBalance/page7.php|title=Climate and Earth's Energy Budget: Feature Articles|first=Lindsey|last=Rebecca|date=14 January 2009|website=earthobservatory.nasa.gov|access-date=3 April 2018|archive-date=10 April 2020|archive-url=https://web.archive.org/web/20200410141354/https://earthobservatory.nasa.gov/features/EnergyBalance/page7.php|url-status=live}} The direct radiative greenhouse gas forcing effect of methane was estimated to be an increase of 0.5 W/m² relative to the year 1750 (estimate in 2007).{{cite web |title=Climate Change Synthesis Report 2007 |url=https://www.ipcc.ch/site/assets/uploads/2018/02/ar4_syr_full_report.pdf |series=IPCC AR4 |publisher=United Nations Environment Programme |pages=}}{{rp|38 (Figure 2.3)}}

In their 2021 "Global Methane Assessment" report, the UNEP and CCAC said that their "understanding of methane's effect on radiative forcing" improved with research by teams led by M. Etminan in 2016, and William Collins in 2018.{{Cite journal| doi = 10.1088/1748-9326/aab89c| issn = 1748-9326| volume = 13| issue = 5| last1 = Collins| first1 = William J.| last2 = Webber| first2 = Christopher P.| last3 = Cox| first3 = Peter M.| last4 = Huntingford| first4 = Chris| last5 = Lowe| first5 = Jason| last6 = Sitch| first6 = Stephen| last7 = Chadburn| first7 = Sarah E.| last8 = Comyn-Platt| first8 = Edward| last9 = Harper| first9 = Anna B.| last10 = Hayman| first10 = Garry| last11 = Powell| first11 = Tom| title = Increased importance of methane reduction for a 1.5 degree target| journal = Environmental Research Letters| access-date = March 19, 2023 | date = April 20, 2018 | page = 054003| bibcode = 2018ERL....13e4003C| s2cid = 53683162| url = https://iopscience.iop.org/article/10.1088/1748-9326/aab89c/pdf| hdl = 10871/34408| hdl-access = free}} This resulted in an "upward revision" since the 2014 IPCC Fifth Assessment Report (AR5). The "improved understanding" says that prior estimates of the "overall societal impact of methane emissions" were likely underestimated.{{cite report |url=https://www.unep.org/resources/report/global-methane-assessment-benefits-and-costs-mitigating-methane-emissions |title=Global Methane Assessment: Benefits and Costs of Mitigating Methane Emissions |date=May 6, 2021 |pages=173 |isbn=978-92-807-3854-4 |editor-last=Shindell |editor-first=Drew |work=United Nations Environment Programme}}{{rp|18}}

Etminan et al. published their new calculations for methane's radiative forcing (RF) in a 2016 Geophysical Research Letters journal article which incorporated the shortwave bands of CH₄ in measuring forcing, not used in previous, simpler IPCC methods. Their new RF calculations which significantly revised those cited in earlier, successive IPCC reports for well mixed greenhouse gases (WMGHG) forcings by including the shortwave forcing component due to CH₄, resulted in estimates that were approximately 20–25% higher.{{Cite journal |last1=Etminan|first1=M.|last2=Myhre|first2=G.|last3=Highwood|first3=E. J.|last4=Shine|first4=K. P. |date=December 27, 2016 |title=Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing |journal=Geophysical Research Letters |language=en |volume=43 |issue=24 |pages=12,614–12,623 |doi=10.1002/2016gl071930|issn=0094-8276|bibcode=2016GeoRL..4312614E |doi-access=free}} Collins et al. said that CH₄ mitigation that reduces atmospheric methane by the end of the century, could "make a substantial difference to the feasibility of achieving the Paris climate targets", and would provide us with more "allowable carbon emissions to 2100".

In addition to the direct heating effect and the normal feedbacks, the methane breaks down to carbon dioxide and water. This water is often above the tropopause, where little water usually reaches. Ramanathan (1998){{cite web |url=https://ramanathan.ucsd.edu/wp-content/uploads/sites/460/2017/10/pr78.pdf |title=Ramanathan |work=Trace-Gas Greenhouse Effect and Global Warming: Underlying Principles and Outstanding Issues |publisher=Ambio-Royal Swedish Academy of sciences}} notes that both water and ice clouds, when formed at cold lower stratospheric temperatures, are extremely efficient in enhancing the atmospheric greenhouse effect. He also notes that there is a distinct possibility that large increases in methane in future may lead to a surface warming that increases nonlinearly with the methane concentration.

Mitigation efforts to reduce short-lived climate pollutants like methane and black carbon would help combat "near-term climate change" and would support Sustainable Development Goals.{{Cite web |title=Primer on Short-Lived Climate Pollutants |url=https://www.ccacoalition.org/en/resources/primer-short-lived-climate-pollutants |access-date=March 19, 2023 |work=Climate & Clean Air Coalition}}

image:The Global Methane Budget 2008–2017.png{{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 }}|right]]

{{Carbon cycle|Methane}}

Any process that results in the production of methane and its release into the atmosphere can be considered a "source". The known sources of methane are predominantly located near the Earth's surface. Two main processes that are responsible for methane production include microorganisms anaerobically converting organic compounds into methane (methanogenesis), which are widespread in aquatic ecosystems, and ruminant animals.

Methane is also released in the Arctic for example from thawing permafrost.

{{excerpt|Methane emissions|paragraphs=1-3|file=no}}

Methane was typically measured using gas chromatography. Gas chromatography is a type of chromatography used for separating or analyzing chemical compounds. It is less expensive in general, compared to more advanced methods, but it is more time and labor-intensive.{{citation needed|date=March 2022}}

Spectroscopic methods were the preferred method for atmospheric gas measurements due to its sensitivity and precision. Also, spectroscopic methods are the only way of remotely sensing the atmospheric gases. Infrared spectroscopy covers a large spectrum of techniques, one of which detects gases based on absorption spectroscopy. There are various methods for spectroscopic methods, including Differential optical absorption spectroscopy, Laser-induced fluorescence, and Fourier Transform Infrared.{{citation needed|date=March 2022}}

{{Cite journal |last1=Nakaema |first1=Walter M. |last2=Hao |first2=Zuo-Qiang |last3=Rohwetter |first3=Philipp |last4=Wöste |first4=Ludger |last5=Stelmaszczyk |first5=Kamil |date=2011-01-27 |title=PCF-Based Cavity Enhanced Spectroscopic Sensors for Simultaneous Multicomponent Trace Gas Analysis |journal=Sensors |language=en |volume=11 |issue=2 |pages=1620–1640 |bibcode=2011Senso..11.1620N |doi=10.3390/s110201620 |issn=1424-8220 |pmc=3274003 |pmid=22319372 |doi-access=free}}

In 2011, cavity ring-down spectroscopy was the most widely used IR absorption technique of detecting methane. It is a form of laser absorption spectroscopy which determines the mole fraction to the order of parts per trillion.

{{See also|Methane emissions#Global methane emissions monitoring}}

image:Mlo ch4 ts obs 03437.png CH₄ has been measured directly in the environment since the 1970s.{{Cite journal |last1=Fox-Kemper |first1=B. |last2=Hewitt |first2=H.T. |author2-link=Helene Hewitt |last3=Xiao |first3=C. |last4=Aðalgeirsdóttir |first4=G. |last5=Drijfhout |first5=S.S. |last6=Edwards |first6=T.L. |last7=Golledge |first7=N.R. |last8=Hemer |first8=M. |last9=Kopp |first9=R.E. |last10=Krinner |first10=G. |last11=Mix |first11=A. |date=2021 |editor-last=Masson-Delmotte |editor-first=V. |editor2-last=Zhai |editor2-first=P. |editor3-last=Pirani |editor3-first=A. |editor4-last=Connors |editor4-first=S.L. |editor5-last=Péan |editor5-first=C. |editor6-last=Berger |editor6-first=S. |editor7-last=Caud |editor7-first=N. |editor8-last=Chen |editor8-first=Y. |editor9-last=Goldfarb |editor9-first=L. |title=Chapter 5: Global Carbon and other Biogeochemical Cycles and Feedbacks |url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf |journal=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |publisher=Cambridge University Press, Cambridge, UK and New York, NY, USA |doi=10.1017/9781009157896.011 |archive-url=https://web.archive.org/web/20230120161826/https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-5/ |archive-date=January 20, 2023}}{{cite report |work=United Nations Environment Programme and Climate and Clean Air Coalition |date=2022 |title=Global Methane Assessment |location=Nairobi |access-date=March 15, 2023 |url=https://wedocs.unep.org/bitstream/handle/20.500.11822/41108/methane_2030_SPM.pdf |pages=12}} The Earth's atmospheric methane concentration has increased 160% since preindustrial levels in the mid-18th century.

Long term atmospheric measurements of methane by NOAA show that the build up of methane nearly tripled since pre-industrial times since 1750.{{cite web |title=Ch.2 Changes in Atmospheric Constituents and in Radiative Forcing |url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-3-2.html |access-date=2017-01-20 |work=Climate Change 2007 IPCC Fourth Assessment Report |publisher=IPPC}} In 1991 and 1998 there was a sudden growth rate of methane representing a doubling of growth rates in previous years. The June 15, 1991 eruption of Mount Pinatubo, measuring VEI-6{{emdash}}was the second-largest terrestrial eruption of the 20th century.{{cite web |url=http://www.noaanews.noaa.gov/stories2006/s2709.htm |title=Scientists pinpoint cause of slowing methane emissions |publisher=National Oceanic & Atmospheric Administration news Online |date=2006-09-28 |access-date=2007-05-23 |archive-url=https://web.archive.org/web/20070526034332/http://www.noaanews.noaa.gov/stories2006/s2709.htm |archive-date=May 26, 2007 |url-status=live}} In 2007 it was reported that unprecedented warm temperatures in 1998{{emdash}}the warmest year since surface records were recorded{{emdash}}could have induced elevated methane emissions, along with an increase in wetland and rice field emissions and the amount of biomass burning.{{cite web |author=Denman, K.L. |title=7. Couplings Between Changes in the Climate System and Biogeochemistry. |work=IPCC AR4 WG1 2007 |url=http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch7.html |access-date=2011-11-04 |display-authors=etal}}

Data from 2007 suggested methane concentrations were beginning to rise again.{{cite web |url=http://www.esrl.noaa.gov/news/2008/aggi.html |title=Annual Greenhouse Gas Index (AGGI) Indicates Sharp Rise in Carbon Dioxide and Methane in 2007 |publisher=National Oceanic & Atmospheric Administration – Earth System Research Laboratory |date=2008-04-23 |access-date=2008-06-16}} This was confirmed in 2010 when a study showed methane levels were on the rise for the 3 years 2007 to 2009. After a decade of near-zero growth in methane levels, "globally averaged atmospheric methane increased by [approximately] 7 nmol/mol per year during 2007 and 2008. During the first half of 2009, globally averaged atmospheric CH₄ was [approximately] 7 nmol/mol greater than it was in 2008, suggesting that the increase will continue in 2009."{{Cite news |url=https://www.telegraph.co.uk/earth/environment/climatechange/7289698/Climate-change-could-be-accelerated-by-methane-time-bomb.html |archive-url=https://web.archive.org/web/20100225114049/http://www.telegraph.co.uk/earth/environment/climatechange/7289698/Climate-change-could-be-accelerated-by-methane-time-bomb.html |url-status=dead |archive-date=February 25, 2010 |title=Climate change could be accelerated by 'methane time bomb' |newspaper=The Telegraph |author=Heidi Blake |date=February 22, 2010}} From 2015 to 2019 sharp rises in levels of atmospheric methane have been recorded.{{Cite news|url=https://www.theguardian.com/environment/2019/feb/17/methane-levels-sharp-rise-threaten-paris-climate-agreement|title=Sharp rise in methane levels threatens world climate targets|last=McKie|first=Robin|date=2019-02-17|work=The Observer|access-date=2019-07-14|language=en-GB|issn=0029-7712}}

In 2010, methane levels in the Arctic were measured at 1850 nmol/mol which is over twice as high as at any time in the last 400,000 years.{{citation needed|date=September 2023}} According to the IPCC AR5, since 2011 concentrations continued to increase. After 2014, the increase accelerated and by 2017, it reached 1,850 (parts per billion) ppb.{{Cite journal |last1=Nisbet |first1=E. G. |last2=Manning |first2=M. R. |last3=Dlugokencky |first3=E. J. |last4=Fisher |first4=R. E. |last5=Lowry |first5=D. |last6=Michel |first6=S. E. |last7=Myhre |first7=C. Lund |last8=Platt |first8=S. M. |last9=Allen |first9=G. |last10=Bousquet |first10=P. |last11=Brownlow |first11=R. |last12=Cain |first12=M. |last13=France |first13=J. L. |last14=Hermansen |first14=O. |last15=Hossaini |first15=R. |date=2019 |title=Very Strong Atmospheric Methane Growth in the 4 Years 2014–2017: Implications for the Paris Agreement |journal=Global Biogeochemical Cycles |volume=33 |issue=3 |pages=318–342 |bibcode=2019GBioC..33..318N |doi=10.1029/2018GB006009 |issn=1944-9224 |s2cid=133716021 |doi-access=free |last16=Jones |first16=A. E. |last17=Levin |first17=I. |last18=Manning |first18=A. C. |last19=Myhre |first19=G. |last20=Pyle |first20=J. A. |last21=Vaughn |first21=B. H. |last22=Warwick |first22=N. J. |last23=White |first23=J. W. C.}} The annual average for methane (CH₄) was 1866 ppb in 2019 and scientists reported with "very high confidence" that concentrations of CH₄ were higher than at any time in at least 800,000 years. The largest annual increase occurred in 2021 with current concentrations reaching a record 260% of pre-industrial{{emdash}}with the overwhelming percentage caused by human activity.

In 2013, IPCC scientists said with "very high confidence", that concentrations of atmospheric methane CH₄ "exceeded the pre-industrial levels by about 150% which represented "levels unprecedented in at least the last 800,000 years."{{cite report |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 |url=https://www.ipcc.ch/site/assets/uploads/2018/03/WG1AR5_SummaryVolume_FINAL.pdf}} The globally averaged concentration of methane in Earth's atmosphere increased by about 150% from 722 ± 25 ppb in 1750 to 1803.1 ± 0.6 ppb in 2011.{{cite web |last=Stocker |title=Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change |url=https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_all_final.pdf |page=182}} As of 2016, methane contributed radiative forcing of 0.62 ± 14% Wm⁻², or about 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases. The atmospheric methane concentration has continued to increase since 2011 to an average global concentration of 1911.8 ± 0.6 ppb as of 2022.{{Cite web|url=https://gml.noaa.gov/webdata/ccgg/trends/ch4/ch4_annmean_gl.txt|title=Globally averaged marine surface annual mean data|work=ESRL Global Monitoring Division – Global Greenhouse Gas Reference Network|last=Laboratory|first=US Department of Commerce, NOAA, Earth System Research|language=EN-US|date=2023-07-05|access-date=2023-07-06}} The May 2021 peak was 1891.6 ppb, while the April 2022 peak was 1909.4 ppb, a 0.9% increase.{{Cite web|url=https://gml.noaa.gov/webdata/ccgg/trends/ch4/ch4_mm_gl.txt|title=Globally averaged marine surface monthly mean data|work=ESRL Global Monitoring Division – Global Greenhouse Gas Reference Network|last=Laboratory|first=US Department of Commerce, NOAA, Earth System Research|language=EN-US|date=2023-07-05|access-date=2023-07-06}}Image:Ch4 gr gl.png The Global Carbon Project consortium produces the Global Methane Budget. Working with over fifty international research institutions and 100 stations globally, it updates the methane budget every few years.{{Cite journal| doi = 10.5194/essd-14-4811-2022| issn = 1866-3516| volume = 14| issue = 11| pages = 4811–4900| last1 = Friedlingstein| first1 = Pierre| last2 = O'Sullivan| first2 = Michael| last3 = Jones| first3 = Matthew W.| last4 = Andrew| first4 = Robbie M.| last5 = Gregor| first5 = Luke| last6 = Hauck| title = Global Carbon Budget 2022| journal = Earth System Science Data| access-date = 2023-03-15| date = 2022-11-11| bibcode = 2022ESSD...14.4811F| url = https://essd.copernicus.org/articles/14/4811/2022/| hdl = 20.500.11850/594889| hdl-access = free| doi-access = free}}

In 2013, the balance between sources and sinks of methane was not yet fully understood. Scientists were unable to explain why the atmospheric concentration of methane had temporarily ceased to increase.

The focus on the role of methane in anthropogenic climate change has become more relevant since the mid-2010s.{{cite magazine |title=The growing role of methane in anthropogenic climate change |last1=Saunois |first1=M |first2=B. |last2=Jackson |first3=P. |last3=Bousquet |first4=B. |last4=Poulter |first5=J G |last5=Canadell |date=2016 |magazine=Environmental Research Letters |volume=11 |number=120207 |page=120207 |doi=10.1088/1748-9326/11/12/120207}}

The amount of methane in the atmosphere is the result of a balance between the production of methane on the Earth's surface{{emdash}}its source{{emdash}}and the destruction or removal of methane, mainly in the atmosphere{{emdash}}its sink{{emdash}} in an atmospheric chemical process.{{cite web |url=http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16827 |title=GMAO Chemical Forecasts and GEOS–CHEM NRT Simulations for ICARTT (top) and Randy Kawa, NASA GSFC Atmospheric Chemistry and Dynamics Branch (lower)|archive-url=https://web.archive.org/web/20050313053747/http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16827 |archive-date=March 13, 2005 }}

Another major natural sink is through oxidation by methanotrophic or methane-consuming bacteria in Earth's soils.

image:AtmosphericMethane.png These 2005 NASA computer model simulations{{emdash}}calculated based on data available at that time{{emdash}}illustrate how methane is destroyed as it rises.

As air rises in the tropics, methane is carried upwards through the troposphere{{emdash}}the lowest portion of Earth's atmosphere which is {{convert|4|mi|km}} to {{convert|12|mi|km}} from the Earth's surface, into the lower stratosphere{{emdash}}the ozone layer{{emdash}}and then the upper portion of the stratosphere.

This atmospheric chemical process is the most effective methane sink, as it removes 90% of atmospheric methane.{{cite journal |display-authors=1 |first1=Stefanie |last1=Kirschke |first2=Philippe |last2=Bousquet |first3=Philippe |last3=Ciais |first4=Marielle |last4=Saunois |first5=Josep G. |last5=Canadell |first6=Edward J. |last6=Dlugokencky |first7=Peter |last7=Bergamaschi |first8=Daniel |last8=Bergmann |first9=Donald R. |last9=Blake |first10=Lori |last10=Bruhwiler |first11=Philip |last11=Cameron-Smith |first12=Simona |last12=Castaldi |first13=Frédéric |last13=Chevallier |first14=Liang |last14=Feng |first15=Annemarie |last15=Fraser |first16=Martin |last16=Heimann |first17=Elke L. |last17=Hodson |first18=Sander |last18=Houweling |first19=Béatrice |last19=Josse |title=Three decades of global methane sources and sinks |journal=Nature Geoscience |volume=6 |issue=10 |pages=813–823 |date=September 22, 2013 |doi=10.1038/ngeo1955 |bibcode=2013NatGe...6..813K |s2cid=18349059 |url=https://zenodo.org/record/3425876}} This global destruction of atmospheric methane mainly occurs in the troposphere.

Methane molecules react with hydroxyl radicals (OH){{emdash}}the "major chemical scavenger in the troposphere" that "controls the atmospheric lifetime of most gases in the troposphere".{{cite book |editor-last1=Holland |editor-first1=H.D. |editor-last2=Turekian |editor-first2=K.K. |title=Treatise on geochemistry |date= |publisher=Elsevier Science |location=Oxford |isbn= |edition=2 |volume=5 |first=S. |last=Levine |chapter=Chemistry of the Hydroxyl Radical (OH) in the Troposphere}} Through this CH₄ oxidation process, atmospheric methane is destroyed and water vapor and carbon dioxide are produced.

While this decreases the concentration of methane in the atmosphere, it is unclear if this leads to a net positive increase in radiative forcing because both water vapor and carbon dioxide are more powerful GHGs factors in terms of affecting the warming of Earth.

This additional water vapor in the stratosphere caused by CH₄ oxidation, adds approximately 15% to methane's radiative forcing effect.{{cite journal |last1=Myhre |first1=Gunnar |display-authors=etal |date=January 9, 2007 |title=Radiative forcing due to stratospheric water vapour from CH4 oxidation |journal= Geophysical Research Letters |volume=34 |issue=1 |doi=10.1029/2006GL027472|bibcode=2007GeoRL..34.1807M|s2cid=59133913 |doi-access=}}{{cite journal |last1=Noël|first1=Stefan| last2=Weigel|first2=Katja|display-authors=etal| date=2017|title=Water Vapour and Methane Coupling in the Stratosphere observed with SCIAMACHY Solar Occultation Measurements |url=https://acp.copernicus.org/preprints/acp-2017-893/acp-2017-893.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://acp.copernicus.org/preprints/acp-2017-893/acp-2017-893.pdf |archive-date=2022-10-09 |url-status=live|journal=Atmospheric Chemistry and Physics|volume= |issue=18 |pages=4463–4476 |doi=10.5194/acp-18-4463-2018 |access-date=22 August 2021 |doi-access=free }}

By the 1980s, the global warming problem had been transformed by the inclusion of methane and other non-CO₂ trace-gases{{emdash}}CFCs, N₂O, and O₃{{emdash}} on global warming, instead of focusing primarily on carbon dioxide.{{Cite journal| issn = 0044-7447| volume = 27| issue = 3| pages = 187–197| last = Ramanathan| first = V.| title = Trace-Gas Greenhouse Effect and Global Warming: Underlying Principles and Outstanding Issues Volvo Environmental Prize Lecture-1997| journal = Ambio| access-date = March 23, 2023 | date = 1998| url = https://www.jstor.org/stable/4314715| jstor = 4314715}}{{cite web |url=http://www.ipcc.ch/publications_and_data/ar4/syr/en/figure-2-4.html |title=Ramanathan |work=Trace-Gas Greenhouse Effect and Global Warming: Underlying Principles and Outstanding Issues |publisher=Ambio-Royal Swedish Academy of Sciences}} Both water and ice clouds, when formed at cold lower stratospheric temperatures, have a significant impact by increasing the atmospheric greenhouse effect. Large increases in future methane could lead to a surface warming that increases nonlinearly with the methane concentration.

Methane also affects the degradation of the ozone layer{{emdash}}the lowest layer of the stratosphere from about {{convert|15|to|35|km|sp=us|0}} above Earth, just above the troposphere.{{cite web|url=http://www.ozonelayer.noaa.gov/science/basics.htm|title=Ozone Basics|website=NOAA|date=2008-03-20|access-date=2007-01-29|archive-url=https://web.archive.org/web/20171121051325/http://www.ozonelayer.noaa.gov/science/basics.htm|archive-date=2017-11-21|url-status=dead}} NASA researchers in 2001, had said that this process was enhanced by global warming, because warmer air holds more water vapor than colder air, so the amount of water vapor in the atmosphere increases as it is warmed by the greenhouse effect. Their climate models based on data available at that time, had indicated that carbon dioxide and methane enhanced the transport of water into the stratosphere.{{cite web |url=http://www.giss.nasa.gov/research/news/20010417/ |title=Wetter Upper Atmosphere May Delay Global Ozone Recovery |year=2001 |publisher=NASA |first=Drew |last=Shindell}}

Atmospheric methane could last about 120 years in the stratosphere until it is eventually destroyed through the hydroxyl radicals oxidation process.{{cite journal |title=Long-term changes of methane and hydrogen in the stratosphere in the period 1978–2003 and their impact on the abundance of stratospheric water vapor |last1=Rohs |first1=S. |last2=Schiller |first2=C. |last3=Riese |first3=M. |last4=Engel |first4=A. |last5=Schmidt |first5=U. |last6=Wetter |first6=T. |last7=Levin |first7=I. |last8=Nakazawa |first8=T. |journal=Journal of Geophysical Research: Atmospheres |volume=111 |issue=D14 |pages=D14315 |id=D14315 |date=July 2006 |doi=10.1029/2005JD006877 |bibcode=2006JGRD..11114315R |url=http://juser.fz-juelich.de/record/50145/files/2005JD006877.pdf|doi-access=free }}

File:Arora 2018 methane lifetime.png

There are different ways to quantify the period of time that methane impacts the atmosphere. The average time that a physical methane molecule is in the atmosphere is estimated to be around 9.6 years.{{cite web |date=April 2010 |title=Methane and Nitrous Oxide Emissions From Natural Sources |url=http://www.epa.gov/methane/pdfs/Methane-and-Nitrous-Oxide-Emissions-From-Natural-Sources.pdf |url-status=dead |archive-url=https://web.archive.org/web/20121202145721/http://www.epa.gov/methane/pdfs/Methane-and-Nitrous-Oxide-Emissions-From-Natural-Sources.pdf |archive-date=2012-12-02 |access-date=2017-01-20 |publisher=USA Environmental Protection Agency Office of Atmospheric Programs}}{{cite journal |title=Future methane, hydroxyl, and their uncertainties: key climate and emission parameters for future predictions |last1=Holmes |first1=C. D. |last2=Prather |first2=M. J. |last3=Søvde |first3=O. A. |last4=Myhre |first4=G. |journal=Atmospheric Chemistry and Physics |volume=13 |issue=1 |pages=285–302 |date=January 2013 |doi=10.5194/acp-13-285-2013 |bibcode=2013ACP....13..285H |display-authors=1 |url=https://escholarship.org/content/qt5rc7k3s3/qt5rc7k3s3.pdf?t=n4jknv|doi-access=free }} See Table 2.{{Cite journal |last1=Arora |first1=Vivek K. |last2=Melton |first2=Joe R. |last3=Plummer |first3=David |date=1 August 2018 |title=An assessment of natural methane fluxes simulated by the CLASS-CTEM model |journal=Biogeosciences |volume=15 |issue=15 |pages=4683–4709 |doi=10.5194/bg-15-4683-2018 |doi-access=free |bibcode=2018BGeo...15.4683A }} However, the average time that the atmosphere will be affected by the emission of that molecule before reaching equilibrium – known as its 'perturbation lifetime' – is approximately twelve years.{{Cite news|url=https://www.theguardian.com/environment/2012/jan/16/greenhouse-gases-remain-air|title=How long do greenhouse gases stay in the air?|first1=Duncan|last1=Clark|first2=Carbon|last2=Brief|date=January 16, 2012|newspaper=The Guardian}}

The reaction of methane and chlorine atoms acts as a primary sink of Cl atoms and is a primary source of hydrochloric acid (HCl) in the stratosphere.{{Cite book |url={{google books |plainurl=y |id=dm4RAQAAIAAJ}} |title=Chemistry of the Natural Atmosphere |last=Warneck |first=Peter |date=2000|publisher=Academic Press |isbn=9780127356327 |language=en}}

CH₄ + Cl → CH₃ + HCl

The HCl produced in this reaction leads to catalytic ozone destruction in the stratosphere.

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File:Puglini_2020_laptev.png are typically consumed within the sediment by methanotrophs. Areas with high sedimentation (top) subject their microbial communities to continual disturbance, and so they are the most likely to see active fluxes, whether with (right) or without active upward flow (left). Even so, the annual release may be limited to 1000 tonnes or less.]]

Soils act as a major sink for atmospheric methane through the methanotrophic bacteria that reside within them. This occurs with two different types of bacteria. "High capacity-low affinity" methanotrophic bacteria grow in areas of high methane concentration, such as waterlogged soils in wetlands and other moist environments. And in areas of low methane concentration, "low capacity-high affinity" methanotrophic bacteria make use of the methane in the atmosphere to grow, rather than relying on methane in their immediate environment. Methane oxidation allows methanotrophic bacteria to use methane as a source of energy, reacting methane with oxygen and as a result producing carbon dioxide and water.

: CH₄ + 2O₂ → CO₂ + 2H₂O

Forest soils act as good sinks for atmospheric methane because soils are optimally moist for methanotroph activity, and the movement of gases between soil and atmosphere (soil diffusivity) is high. With a lower water table, any methane in the soil has to make it past the methanotrophic bacteria before it can reach the atmosphere. Wetland soils, however, are often sources of atmospheric methane rather than sinks because the water table is much higher, and the methane can be diffused fairly easily into the air without having to compete with the soil's methanotrophs.{{cite web |first1=Dave |last1=Reay |title=Methane Sinks − Soils |work=Greenhouse Gas Online |url=http://www.ghgonline.org/methanesinksoil.htm |access-date=2016-12-22}}

Methanotrophic bacteria also occur in the underwater sediments. Their presence can often efficiently limit emissions from sources such as the underwater permafrost in areas like the Laptev Sea.{{cite journal |last1=Puglini |first1=Matteo |last2=Brovkin |first2=Victor |last3=Regnier |first3=Pierre |last4=Arndt |first4=Sandra |date=26 June 2020 |title=Assessing the potential for non-turbulent methane escape from the East Siberian Arctic Shelf |url=https://bg.copernicus.org/articles/17/3247/2020/ |journal=Biogeosciences |volume=17 |issue=12 |pages=3247–3275 |doi=10.5194/bg-17-3247-2020 |bibcode=2020BGeo...17.3247P |s2cid=198415071 |doi-access=free |hdl=21.11116/0000-0003-FC9E-0 |hdl-access=free }}

{{excerpt|Atmospheric methane removal}}

image:Atmospheric Concentrations of Methane Over Time.png data of methane]]From 1996 to 2004, researchers in the European Project for Ice Coring in Antarctica (EPICA) project were able to drill and analyze gases trapped in the ice cores in Antarctica to reconstruct GHG concentrations in the atmosphere over the past 800,000 years".{{cite web |url=https://phys.org/news/2019-04-oldest-ice-earth-puzzle-planet.html |title=The oldest ice on Earth may be able to solve the puzzle of the planet's climate history |work=University of Bern |date=April 2019 |access-date=March 20, 2023}} They found that prior to approximately 900,000 years ago, the cycle of ice ages followed by relatively short warm periods lasted about 40,000 years, but by 800,000 years ago the time interval changed dramatically to cycles that lasted 100,000 years. There were low values of GHG in ice ages, and high values during the warm periods.

This 2016 EPA illustration above is a compilation of paleoclimatology showing methane concentrations over time based on analysis of gas bubbles from{{cite report |title=Climate Change Indicators in the United States: Atmospheric Concentrations of Greenhouse Gases|date=August 2016 |url=https://www.epa.gov/sites/default/files/2016-08/documents/print_ghg-concentrations-2016.pdf |access-date=March 20, 2023}} EPICA Dome C, Antarctica{{emdash}}approximately 797,446 BCE to 1937 CE,{{Cite journal| doi = 10.1038/nature06950| issn = 1476-4687| volume = 453| issue = 7193| pages = 383–386| last1 = Loulergue| first1 = Laetitia| last2 = Schilt| first2 = Adrian| last3 = Spahni| first3 = Renato| last4 = Masson-Delmotte| first4 = Valérie| last5 = Blunier| first5 = Thomas| last6 = Lemieux| first6 = Bénédicte| last7 = Barnola| first7 = Jean-Marc| last8 = Raynaud| first8 = Dominique| last9 = Stocker| first9 = Thomas F.| last10 = Chappellaz| first10 = Jérôme| title = Orbital and millennial-scale features of atmospheric CH₄ over the past 800,000 years| journal = Nature| date = May 15, 2008| pmid = 18480822 | bibcode = 2008Natur.453..383L| s2cid = 205213265|url=https://www.ncdc.noaa.gov/paleo/pubs/loulergue2008/loulergue2008.html |access-date=March 20, 2023| doi-access = free}} Law Dome, Antarctica{{emdash}}approximately 1008 CE to 1980 CE{{Cite report| publisher = Environmental System Science Data Infrastructure for a Virtual Ecosystem; Carbon Dioxide Information Analysis Center (CDIAC), Oak Ridge National Laboratory (ORNL)|location=Oak Ridge, TN | doi = 10.3334/CDIAC/ATG.030| last1 = Etheridge| first1 = D.| last2 = Steele| first2 = L.| last3 = Francey| first3 = R.| last4 = Langenfelds| first4 = R.| title = Historic CH₄ Records from Antarctic and Greenland Ice Cores, Antarctic Firn Data, and Archived Air Samples from Cape Grim, Tasmania| access-date = March 21, 2023| date = 2002| url = https://www.osti.gov/servlets/purl/1394397/ |series=Trends: A compendium of data on global change | url-access = subscription}} Cape Grim, Australia{{emdash}}1985 CE to 2015 CE{{cite report |work=National Oceanic and Atmospheric Administration |date=2016 |title=Monthly mean CH₄ concentrations for Cape Grim, Australia}} Mauna Loa, Hawaii{{emdash}}1984 CE to 2015 CE{{cite report |work=National Oceanic and Atmospheric Administration |date=2016 |title= Monthly mean CH₄ concentrations for Mauna Loa, Hawaii}} and Shetland Islands, Scotland: 1993 CE to 2001 CE{{cite book |last1=Steele |first1=L.P. |first2=P.B. |last2=Krummel |first3=R.L. |last3=Langenfelds |date=October 2002 |title= Atmospheric methane record from Shetland Islands, Scotland |series=Trends: A compendium of data on global change |location=Oak Ridge, TN |work=U.S. Department of Energy |access-date=March 20, 2023 |url=https://cdiac.ess-dive.lbl.gov/trends/atm_meth/csiro/csiro-shetlandch4.html}}

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File:Graph CO2 CH4 and Temperature Graph in English 15 June 2015 by Reg Morrison.jpgThe massive and rapid release of large volumes of methane gas from such sediments into the atmosphere has been suggested as a possible cause for rapid global warming events in the Earth's distant past, such as the Paleocene–Eocene Thermal Maximum,{{cite journal |title=Two massive, rapid releases of carbon during the onset of the Palaeocene–Eocene thermal maximum |display-authors=1 |first1=Gabriel J. |last1=Bowen |first2=Bianca J. |last2=Maibauer |first3=Mary J. |last3=Kraus |first4=Ursula |last4=Röhl |first5=Thomas |last5=Westerhold |first6=Amy |last6=Steimke |first7=Philip D. |last7=Gingerich |first8=Scott L. |last8=Wing |first9=William C. |last9=Clyde |journal=Nature Geoscience |volume=8 |issue=1 |pages=44–47 |date=December 15, 2014 |doi=10.1038/ngeo2316 |bibcode=2015NatGe...8...44B}} and the Great Dying.{{cite journal |title=How to kill (almost) all life: the end-Permian extinction event |journal=Trends in Ecology & Evolution |first1=Michael J. |last1=Benton |first2=Richard J. |last2=Twitchett |volume=18 |issue=7 |date=July 2003 |pages=358–365 |doi=10.1016/S0169-5347(03)00093-4}}

In 2001, NASA's Goddard Institute for Space Studies and Columbia University's Center for Climate Systems Research scientists confirmed that other greenhouse gases apart from carbon dioxide were important factors in climate change in research presented at the annual meeting of the American Geophysical Union (AGU).{{Cite press release |title=Methane Explosion Warmed The Prehistoric Earth, Possible Again |work=NASA/Goddard Space Flight Center, EOS Project Science Office |via=ScienceDaily |date=December 12, 2001 |access-date=March 22, 2023 |url=https://www.sciencedaily.com/releases/2001/12/011210163439.htm}} They offered a theory on the 100,000-year long Paleocene–Eocene Thermal Maximum that occurred approximately 55 million years ago. They posited that there was a vast release of methane that had previously been kept stable through "cold temperatures and high pressure...beneath the ocean floor". This methane release into the atmosphere resulted in the warming of the earth. A 2009 journal article in Science, confirmed NASA research that the contribution of methane to global warming had previously been underestimated.{{cite journal |title=Improved Attribution of Climate Forcing to Emissions |first1=2 Greg |last1=Shindell |last2=Faluvegi |first3=Dorothy M. |last3=Koch |first4=Gavin A. |last4=Schmidt |first5=Nadine |last5=Unger |author-link5=Nadine Unger|first6=Susanne E. |last6=Bauer |journal=Science |date=October 30, 2009 |volume=326 |issue=5953 |pages=716–718 |doi=10.1126/science.1174760 |pmid=19900930 |first2=G. |bibcode=2009Sci...326..716S|s2cid=30881469 |url=https://zenodo.org/record/1230902 }}{{cite news |url=https://www.usatoday.com/tech/science/environment/2009-10-29-methane-global-warming_N.htm |work=USA Today |title=Methane's role in global warming underestimated |first=Dan |last=Vergano |date=2009-10-29}}

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Early in the Earth's history carbon dioxide and methane likely produced a greenhouse effect. The carbon dioxide would have been produced by volcanoes and the methane by early microbes. During this time, Earth's earliest life appeared.{{Cite book |last=Gale |first=Joseph |title=Astrobiology of Earth: the emergence, evolution, and future of life on a planet in turmoil |date=2009 |publisher=Oxford University Press |location=Oxford |url={{google books |plainurl=y |id=64zn0nxDVUYC}}|isbn=978-0-19-920580-6}} According to a 2003 article in the journal Geology, these first, ancient bacteria added to the methane concentration by converting hydrogen and carbon dioxide into methane and water. Oxygen did not become a major part of the atmosphere until photosynthetic organisms evolved later in Earth's history. With no oxygen, methane stayed in the atmosphere longer and at higher concentrations than it does today.{{cite journal |title=Methane-rich Proterozoic atmosphere? |last1=Pavlov |first1=Alexander A. |last2=Hurtgen |first2=Matthew T. |last3=Kasting |first3=James F. |last4=Arthur |first4=Michael A. |display-authors=1 |journal=Geology |volume=31 |issue=1 |pages=87–90 |date=January 2003 |doi=10.1130/0091-7613(2003)031<0087:MRPA>2.0.CO;2 |bibcode=2003Geo....31...87P}}

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Category:Methane

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