Greenhouse gas

File:Atmospheric Transmission.svgs of electromagnetic waves. The largest absorption band of carbon dioxide is not far from the maximum in the thermal emission from ground, and it partly closes the window of transparency of water—explaining carbon dioxide's major heat-trapping effect.]]

Greenhouse gases are infrared active, meaning that they absorb and emit infrared radiation in the same long wavelength range as what is emitted by the Earth's surface, clouds and atmosphere.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.{{rp|2233}}

99% of the Earth's dry atmosphere (excluding water vapor) is made up of nitrogen ({{chem|N|2}}) (78%) and oxygen ({{chem|O|2}}) (21%). Because their molecules contain two atoms of the same element, they have no asymmetry in the distribution of their electrical charges, and so are almost totally unaffected by infrared thermal radiation,{{cite journal |last1=Wei |first1=Peng-Sheng |last2=Hsieh |first2=Yin-Chih |last3=Chiu |first3=Hsuan-Han |last4=Yen |first4=Da-Lun |last5=Lee |first5=Chieh |last6=Tsai |first6=Yi-Cheng |last7=Ting |first7=Te-Chuan |date=6 October 2018 |title=Absorption coefficient of carbon dioxide across atmospheric troposphere layer |journal=Heliyon |volume=4 |issue=10 |pages=e00785 |doi=10.1016/j.heliyon.2018.e00785 |doi-access=free |pmid=30302408 |pmc=6174548 |bibcode=2018Heliy...400785W |issn = 2405-8440 }} with only an extremely minor effect from collision-induced absorption.{{Cite journal |last1=Höpfner |first1=M. |last2=Milz |first2=M. |last3=Buehler |first3=S. |last4=Orphall |first4=J. |last5=Stiller |first5=G. |date=24 May 2012 |title=The natural greenhouse effect of atmospheric oxygen (O₂) and nitrogen (N₂) |journal=Geophysical Research Letters |language=en |volume=39 |issue=L10706 |doi=10.1029/2012GL051409 |bibcode=2012GeoRL..3910706H |s2cid=128823108 |issn=1944-8007}}{{cite web |title=Which Gases Are Greenhouse Gases? |url=https://www.acs.org/content/acs/en/climatescience/greenhousegases/whichgases.html |access-date=2021-05-31 |publisher=American Chemical Society}}{{Cite journal |last1=Höpfner |first1=M. |last2=Milz |first2=M. |last3=Buehler |first3=S. |last4=Orphall |first4=J. |last5=Stiller |first5=G. |date=24 May 2012 |title=The natural greenhouse effect of atmospheric oxygen (O₂) and nitrogen (N₂) |journal=Geophysical Research Letters |language=en |volume=39 |issue=L10706 |doi=10.1029/2012GL051409 |bibcode=2012GeoRL..3910706H |issn=1944-8007 |s2cid=128823108}} A further 0.9% of the atmosphere is made up by argon (Ar), which is monatomic, and so completely transparent to thermal radiation. On the other hand, carbon dioxide (0.04%), methane, nitrous oxide and even less abundant trace gases account for less than 0.1% of Earth's atmosphere, but because their molecules contain atoms of different elements, there is an asymmetry in electric charge distribution which allows molecular vibrations to interact with electromagnetic radiation. This makes them infrared active, and so their presence causes greenhouse effect.{{cite book |last1=Archer |first1=David |url=http://forecast.uchicago.edu/chapter4.pdf |title=Global Warming: Understanding the Forecast, Chapter 4: Greenhouse Gases |date=2011 |publisher=Wiley |isbn=978-0470943410 |edition=2 |access-date=14 June 2023}}

{{Main|Radiative forcing}}

File:1750- Radiative forcing - greenhouse gases and aerosols.svg (Earth's responsiveness to increases in greenhouse gas concentrations). In what Hansen called a Faustian bargain, regulation of aerosols improved air quality, but aerosols' cooling effect became inadequate to temper the increasing warming effect of greenhouse gases—explaining unexpectedly large global warming in 2023–2024.{{cite journal |last1=Hansen |first1=James E. |last2=Kharecha |first2=Pushker |last3=Sato |first3=Makiko |last4=Tselioudis |first4=George |last5=Kelly |first5=Joseph |last6=Bauer |first6=Susanne E. |last7=Ruedy |first7=Reto |last8=Jeong |first8=Eunbi |last9=Jin |first9=Quijian |last10=Rignot |first10=Eric |last11=Velicogna |first11=Isabella |last12=Schoeberl |first12=Mark R. |last13=von Schuckmann |first13=Karina |last14=Amponsem |first14=Joshua |last15=Cao |first15=Junji |last16=Keskinen |first16=Anton |last17=Li |first17=Jing |last18=Pokela |first18=Anni |display-authors=4 |title=Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed? |journal=Environment |date=3 February 2025 |volume=67 |issue=1 |pages=6–44 |doi=10.1080/00139157.2025.2434494|doi-access=free }} Figure 3.]]

File:Greenhouse gas absorption coefficients.svg absorption coefficients of primary greenhouse gases. Water vapor absorbs over a broad range of wavelengths. Earth emits thermal radiation particularly strongly in the vicinity of the carbon dioxide 15-micron absorption band. The relative importance of water vapor decreases with increasing altitude.]]

Earth absorbs some of the radiant energy received from the sun, reflects some of it as light and reflects or radiates the rest back to space as heat. A planet's surface temperature depends on this balance between incoming and outgoing energy. When Earth's energy balance is shifted, its surface becomes warmer or cooler, leading to a variety of changes in global climate.{{cite web |year=2016 |title=Climate Change Indicators in the United States – Greenhouse Gases |url=https://www.epa.gov/climate-indicators/greenhouse-gases |url-status=live |archive-url=https://web.archive.org/web/20160827230238/https://www.epa.gov/climate-indicators/greenhouse-gases |archive-date=27 August 2016 |access-date=5 September 2020 |publisher=U.S. Environmental Protection Agency (EPA)}}. Radiative forcing is a metric calculated in watts per square meter, which characterizes the impact of an external change in a factor that influences climate. It is calculated as the difference in top-of-atmosphere (TOA) energy balance immediately caused by such an external change. A positive forcing, such as from increased concentrations of greenhouse gases, means more energy arriving than leaving at the top-of-atmosphere, which causes additional warming, while negative forcing, like from sulfates forming in the atmosphere from sulfur dioxide, leads to cooling.{{rp|2245}}{{cite web |year=2016 |title=Climate Change Indicators in the United States – Climate Forcing |url=https://www.epa.gov/climate-indicators/climate-change-indicators-climate-forcing |url-status=live |archive-url=https://web.archive.org/web/20160827223551/https://www.epa.gov/climate-indicators/climate-change-indicators-climate-forcing |archive-date=27 August 2016 |access-date=5 September 2020 |publisher=U.S. Environmental Protection Agency (EPA)}}[https://www.epa.gov/sites/production/files/2016-08/documents/print_climate-forcing-2016.pdf] {{Webarchive|url=https://web.archive.org/web/20200921073951/https://www.epa.gov/sites/production/files/2016-08/documents/print_climate-forcing-2016.pdf|date=21 September 2020}}

Within the lower atmosphere, greenhouse gases exchange thermal radiation with the surface and limit radiative heat flow away from it, which reduces the overall rate of upward radiative heat transfer.{{cite book |last1=Wallace |first1=J. M. |last2=Hobbs |first2=P. V. |title=Atmospheric Science |date=2006 |publisher=Academic Press |isbn=978-0-12-732951-2 |edition=2}}{{rp|139}}{{cite journal |last1=Manabe |first1=S. |last2=Strickler |first2=R. F. |title=Thermal Equilibrium of the Atmosphere with a Convective Adjustment |journal=J. Atmos. Sci. |date=1964 |volume=21 |issue=4 |pages=361–385 |doi=10.1175/1520-0469(1964)021<0361:TEOTAW>2.0.CO;2|bibcode=1964JAtS...21..361M |doi-access=free }} The increased concentration of greenhouse gases is also cooling the upper atmosphere, as it is much thinner than the lower layers, and any heat re-emitted from greenhouse gases is more likely to travel further to space than to interact with the fewer gas molecules in the upper layers. The upper atmosphere is also shrinking as the result.{{Cite web |last=Hatfield |first=Miles |date=30 June 2021 |title=NASA Satellites See Upper Atmosphere Cooling and Contracting Due to Climate Change |url=https://www.nasa.gov/general/nasa-satellites-see-upper-atmosphere-cooling-and-contracting-due-to-climate-change/ |publisher=NASA }}

{{Main|Greenhouse effect}}Anthropogenic changes to the natural greenhouse effect are sometimes referred to as the enhanced greenhouse effect.{{rp|2223}}

This table shows the most important contributions to the overall greenhouse effect, without which the average temperature of Earth's surface would be about {{convert|-18|°C|°F}},{{Cite web |title= Science Briefs: Greenhouse Gases: Refining the Role of Carbon Dioxide |url=http://www.giss.nasa.gov/research/briefs/ma_01/ |url-status=dead |archive-url=https://web.archive.org/web/20050112211604/http://www.giss.nasa.gov/research/briefs/ma_01/ |archive-date=2005-01-12 |access-date=2016-04-26 |website=NASA GISS |author1=Qiancheng Ma |date=March 1998 }} instead of around {{convert|15|°C|°F}}.{{cite journal |vauthors=Karl TR, Trenberth KE |year=2003 |title=Modern global climate change |url=https://zenodo.org/record/1230878 |via=Zenodo |s2cid-access=free |url-status=live |journal=Science |volume=302 |issue=5651 |pages=1719–23 |bibcode=2003Sci...302.1719K |doi=10.1126/science.1090228 |pmid=14657489 |s2cid=45484084 |archive-url=https://web.archive.org/web/20210422194919/https://zenodo.org/record/1230878 |archive-date=22 April 2021 |access-date=26 July 2019}} This table also specifies tropospheric ozone, because this gas has a cooling effect in the stratosphere, but a warming influence comparable to nitrous oxide and CFCs in the troposphere.{{cite web |date=2016-08-01 |title=Atmospheric Concentration of Greenhouse Gases |url=https://www.epa.gov/sites/default/files/2016-08/documents/print_ghg-concentrations-2016.pdf |publisher=U.S. Environmental Protection Agency}}

File:CO2_H2O_absorption_atmospheric_gases_unique_pattern_energy_wavelengths_of_energy_transparent_to_others.png

Water vapor is the most important greenhouse gas overall, being responsible for 41–67% of the greenhouse effect, but its global concentrations are not directly affected by human activity. While local water vapor concentrations can be affected by developments such as irrigation, it has little impact on the global scale due to its short residence time of about nine days.{{cite web |date=27 April 1995 |title=AGU Water Vapor in the Climate System |url=http://www.eso.org/gen-fac/pubs/astclim/espas/pwv/mockler.html |url-status=live |archive-url=https://web.archive.org/web/20121020163357/http://www.eso.org/gen-fac/pubs/astclim/espas/pwv/mockler.html |archive-date=20 October 2012 |access-date=2011-09-11 |publisher=Eso.org}} Indirectly, an increase in global temperatures will also increase water vapor concentrations and thus their warming effect, in a process known as water vapor feedback. It occurs because the Clausius–Clapeyron relation holds that more water vapor will be present per unit volume at elevated temperatures.{{Cite journal |last1=Held |first1=Isaac M. |last2=Soden |first2=Brian J. |date=November 2000 |title=Water vapor feedback and global warming |journal=Annual Review of Energy and the Environment |language=en |volume=25 |issue=1 |pages=441–475 |citeseerx=10.1.1.22.9397 |doi=10.1146/annurev.energy.25.1.441 |issn=1056-3466 |doi-access=free}} Thus, local atmospheric concentration of water vapor varies from less than 0.01% in extremely cold regions up to 3% by mass in saturated air at about 32 °C.{{cite book |author=Evans, Kimberly Masters |url=https://archive.org/details/environment00kimm_0 |title=The environment: a revolution in attitudes |publisher=Thomson Gale |year=2005 |isbn=978-0787690823 |location=Detroit |chapter=The greenhouse effect and climate change |chapter-url={{google books |plainurl=y |id=DdtzAAAACAAJ}} |url-access=registration}}

{{excerpt|Global warming potential}}

File:1979- Radiative forcing - climate change - global warming - EPA NOAA.svg Global Monitoring Laboratory/Earth System Research Laboratories}}]]

The contribution of each gas to the enhanced greenhouse effect is determined by the characteristics of that gas, its abundance, and any indirect effects it may cause. For example, the direct radiative effect of a mass of methane is about 84 times stronger than the same mass of carbon dioxide over a 20-year time frame.{{cite book |title=Intergovernmental Panel on Climate Change Fifth Assessment Report |page=731 |chapter=Appendix 8.A |access-date=6 November 2017 |chapter-url=http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf |archive-url=https://web.archive.org/web/20171013100414/http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf |archive-date=13 October 2017 |url-status=live}} Since the 1980s, greenhouse gas forcing contributions (relative to year 1750) are also estimated with high accuracy using IPCC-recommended expressions derived from radiative transfer models.{{Cite web |author=Butler J. and Montzka S. |year=2020 |title=The NOAA Annual Greenhouse Gas Index (AGGI) |url=https://www.esrl.noaa.gov/gmd/aggi/aggi.html |publisher=NOAA Global Monitoring Laboratory/Earth System Research Laboratories}}

The concentration of a greenhouse gas is typically measured in parts per million (ppm) or parts per billion (ppb) by volume. A {{CO2}} concentration of 420 ppm means that 420 out of every million air molecules is a {{CO2}} molecule. The first 30 ppm increase in {{CO2}} concentrations took place in about 200 years, from the start of the Industrial Revolution to 1958; however the next 90 ppm increase took place within 56 years, from 1958 to 2014.{{cite book |author=Charles J. Kibert |title=Sustainable Construction: Green Building Design and Delivery |publisher=Wiley |year=2016 |isbn=978-1119055327 |chapter=Background |chapter-url={{google books |plainurl=y |id=qv3iCwAAQBAJ|page=698}}}}{{cite web |year=2005 |title=Full Mauna Loa CO₂ record |url=https://www.esrl.noaa.gov/gmd/ccgg/trends/full.html |url-status=live |archive-url=https://web.archive.org/web/20170428033710/https://www.esrl.noaa.gov/gmd/ccgg/trends/full.html |archive-date=28 April 2017 |access-date=6 May 2017 |publisher=Earth System Research Laboratories}} Similarly, the average annual increase in the 1960s was only 37% of what it was in 2000 through 2007.{{Cite FTP |last=Tans |first=Pieter |date=3 May 2008 |server=National Oceanic and Atmospheric Administration Earth System Research Laboratories, Global Monitoring Division |title=Annual CO₂ mole fraction increase (ppm) for 1959–2007 |url=ftp://ftp.cmdl.noaa.gov/ccg/co2/trends/co2_gr_mlo.txt }} {{cite web |title=additional details |url=http://www.esrl.noaa.gov/gmd/ccgg/trends/ |url-status=live |archive-url=https://web.archive.org/web/20181225142754/https://www.esrl.noaa.gov/gmd/ccgg/trends/ |archive-date=25 December 2018 |access-date=15 May 2008}}; see also {{cite journal |last1=Masarie |first1=K.A. |last2=Tans |first2=P.P. |year=1995 |title=Extension and integration of atmospheric carbon dioxide data into a globally consistent measurement record |url=https://zenodo.org/record/1231364 |url-status=live |journal=J. Geophys. Res. |volume=100 |issue=D6 |pages=11593–610 |bibcode=1995JGR...10011593M |doi=10.1029/95JD00859 |archive-url=https://web.archive.org/web/20210308193900/https://zenodo.org/record/1231364 |archive-date=8 March 2021 |access-date=26 July 2019}}

Many observations are available online in a variety of Atmospheric Chemistry Observational Databases. The table below shows the most influential long-lived, well-mixed greenhouse gases, along with their tropospheric concentrations and direct radiative forcings, as identified by the Intergovernmental Panel on Climate Change (IPCC).{{cite book |url=https://www.ipcc.ch/report/ar5/wg1/ |title=AR5 Climate Change 2013: The Physical Science Basis |contribution=Chapter 8}} Abundances of these trace gases are regularly measured by atmospheric scientists from samples collected throughout the world.{{cite web |title=Global Monitoring Laboratory |url=https://www.esrl.noaa.gov/gmd/ |access-date=2020-12-11 |publisher=NOAA Earth System Research Laboratories}}{{cite web |title=World Data Centre for Greenhouse Gases |url=https://gaw.kishou.go.jp/ |access-date=2020-12-11 |publisher=World Meteorological Organization Global Atmosphere Watch Programme and Japan Meteorological Agency}}{{cite web |title=Advanced Global Atmospheric Gas Experiment |url=https://agage.mit.edu/ |access-date=2020-12-11 |publisher=Massachusetts Institute of Technology}} It excludes water vapor because changes in its concentrations are calculated as a climate change feedback indirectly caused by changes in other greenhouse gases, as well as ozone, whose concentrations are only modified indirectly by various refrigerants that cause ozone depletion. Some short-lived gases (e.g. carbon monoxide, NOx) and aerosols (e.g. mineral dust or black carbon) are also excluded because of limited role and strong variation, along with minor refrigerants and other halogenated gases, which have been mass-produced in smaller quantities than those in the table.{{rp|731–738}} and Annex III of the 2021 IPCC WG1 Report{{citation |title=Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change |date=2021-08-09 |editor=Dentener F. J. |url=https://www.ipcc.ch/report/ar6/wg1/#FullReport |section=Annex III: Tables of historical and projected well-mixed greenhouse gas mixing ratios and effective radiative forcing of all climate forcers |section-url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexIII.pdf |publisher=Cambridge University Press |editor2=B. Hall |editor3=C. Smith}}{{rp|4–9}}

{{notelist-ua}}

Atmospheric concentrations are determined by the balance between sources (emissions of the gas from human activities and natural systems) and sinks (the removal of the gas from the atmosphere by conversion to a different chemical compound or absorption by bodies of water).Denman, K.L., G. Brasseur, A. Chidthaisong, P. Ciais, P.M. Cox, R.E. Dickinson, D. Hauglustaine, C. Heinze, E. Holland, D. Jacob, U. Lohmann, S Ramachandran, P.L. da Silva Dias, S.C. Wofsy and X. Zhang, 2007: [https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-chapter7-1.pdf Chapter 7: Couplings Between Changes in the Climate System and Biogeochemistry]. In: [https://www.ipcc.ch/report/ar4/wg1/ 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.{{rp|512}}

File:Carbon Dioxide Partitioning.svgs, including plant growth, soil uptake, and ocean uptake (2020 Global Carbon Budget).]]

The proportion of an emission remaining in the atmosphere after a specified time is the "airborne fraction" (AF). The annual airborne fraction is the ratio of the atmospheric increase in a given year to that year's total emissions. The annual airborne fraction for {{CO2}} had been stable at 0.45 for the past six decades even as the emissions have been increasing. This means that the other 0.55 of emitted {{CO2}} is absorbed by the land and atmosphere carbon sinks within the first year of an emission.{{Cite journal |last1=Friedlingstein |first1=Pierre |last2=O'Sullivan |first2=Michael |last3=Jones |first3=Matthew W. |last4=Andrew |first4=Robbie M. |last5=Hauck |first5=Judith |last6=Olsen |first6=Are |last7=Peters |first7=Glen P. |last8=Peters |first8=Wouter |last9=Pongratz |first9=Julia |last10=Sitch |first10=Stephen |last11=Le Quéré |first11=Corinne |last12=Canadell |first12=Josep G. |last13=Ciais |first13=Philippe |last14=Jackson |first14=Robert B. |last15=Alin |first15=Simone |date=2020 |title=Global Carbon Budget 2020 |journal=Earth System Science Data |language=en |volume=12 |issue=4 |pages=3269–3340 |doi=10.5194/essd-12-3269-2020 |bibcode=2020ESSD...12.3269F |issn=1866-3516 |doi-access=free |hdl=20.500.11850/458765 |hdl-access=free }} In the high-emission scenarios, the effectiveness of carbon sinks will be lower, increasing the atmospheric fraction of {{CO2}} even though the raw amount of emissions absorbed will be higher than in the present.{{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=IPCC Sixth Assessment Report: Working Group 1 |chapter=Global Carbon and Other Biogeochemical Cycles and Feedbacks |chapter-url=https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Chapter_05.pdf}}{{rp|746}}

File:Arora 2018 methane lifetime.png

Major greenhouse gases are well mixed and take many years to leave the atmosphere.{{cite book |author=Betts |url=http://www.grida.no/publications/other/ipcc%5Ftar/?src=/climate/ipcc_tar/wg1/218.htm |title=Chapter 6 Radiative Forcing of Climate Change |publisher=UNEP/GRID-Arendal – Publications |year=2001 |series=Working Group I: The Scientific Basis IPCC Third Assessment Report – Climate Change 2001 |contribution=6.3 Well-mixed Greenhouse Gases |access-date=2010-10-16 |archive-url=https://web.archive.org/web/20110629043240/http://www.grida.no/publications/other/ipcc_tar/?src=%2Fclimate%2Fipcc_tar%2Fwg1%2F218.htm |archive-date=29 June 2011 |url-status=dead}}

The atmospheric lifetime of a greenhouse gas refers to the time required to restore equilibrium following a sudden increase or decrease in its concentration in the atmosphere. Individual atoms or molecules may be lost or deposited to sinks such as the soil, the oceans and other waters, or vegetation and other biological systems, reducing the excess to background concentrations. The average time taken to achieve this is the mean lifetime. This can be represented through the following formula, where the lifetime $\backslash tau$ of an atmospheric species X in a one-box model is the average time that a molecule of X remains in the box.{{cite book |last=Jacob |first=Daniel |url=http://www-as.harvard.edu/people/faculty/djj/book/ |title=Introduction to atmospheric chemistry |publisher=Princeton University Press |year=1999 |isbn=978-0691001852 |pages=25–26 |archive-url=https://web.archive.org/web/20110902182732/http://www-as.harvard.edu/people/faculty/djj/book/ |archive-date=2 September 2011 |url-status=dead |df=dmy-all}}

$\backslash tau$ can also be defined as the ratio of the mass $m$ (in kg) of X in the box to its removal rate, which is the sum of the flow of X out of the box

($F\_\backslash text\{out\}$),

chemical loss of X

($L$),

and deposition of X

($D$)

(all in kg/s):

:$\backslash tau\; =\; \backslash frac\{m\}\{F\_\backslash text\{out\}+L+D\}$.

If input of this gas into the box ceased, then after time $\backslash tau$, its concentration would decrease by about 63%.

Changes to any of these variables can alter the atmospheric lifetime of a greenhouse gas. For instance, methane's atmospheric lifetime is estimated to have been lower in the 19th century than now, but to have been higher in the second half of the 20th century than after 2000.{{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 |s2cid=55585998 }} Carbon dioxide has an even more variable lifetime, which cannot be specified down to a single number.{{cite web |date=15 March 2005 |title=How long will global warming last? |url=http://www.realclimate.org/index.php/archives/2005/03/how-long-will-global-warming-last |url-status=live |archive-url=https://web.archive.org/web/20210304213944/http://www.realclimate.org/index.php/archives/2005/03/how-long-will-global-warming-last/ |archive-date=4 March 2021 |access-date=2012-06-12 |publisher=RealClimate}}{{rp|2237}} Scientists instead say that while the first 10% of carbon dioxide's airborne fraction (not counting the ~50% absorbed by land and ocean sinks within the emission's first year) is removed "quickly", the vast majority of the airborne fraction – 80% – lasts for "centuries to millennia". The remaining 10% stays for tens of thousands of years. In some models, this longest-lasting fraction is as large as 30%.{{cite web |date=17 January 2023 |title=How long will global warming last? |url=

https://climate.mit.edu/ask-mit/how-do-we-know-how-long-carbon-dioxide-remains-atmosphere |publisher=MIT Climate Portal }}{{cite web |last=Atkinson |first=Kate |date=19 July 2023 |title=How long will global warming last? |url=https://www.aap.com.au/factcheck/carbon-atmospheric-residence-claim-is-full-of-gas/ |publisher=Australian Associated Press }}

File:CO2 exponential decay comparison.png

{{excerpt|Carbon dioxide in Earth's atmosphere#Concentrations in the geologic past|paragraphs=1-2}}

{{Further|Greenhouse gas monitoring|Greenhouse gas inventory|Greenhouse gas emissions}}

Greenhouse gas monitoring involves the direct measurement of atmospheric concentrations and direct and indirect measurement of greenhouse gas emissions. Indirect methods calculate emissions of greenhouse gases based on related metrics such as fossil fuel extraction.

There are several different methods of measuring carbon dioxide concentrations in the atmosphere, including infrared analyzing and manometry.{{Cite journal |last=Harris |first=Daniel C. |date=2010 |title=Charles David Keeling and the Story of Atmospheric CO2 Measurements |journal=Analytical Chemistry |language=en |volume=82 |issue=19 |pages=7865–7870 |doi=10.1021/ac1001492 |issn=0003-2700 |pmid=20536268|bibcode=2010AnaCh..82.7865H }} Methane and nitrous oxide are measured by other instruments, such as the range-resolved infrared differential absorption lidar (DIAL).{{Cite journal |last1=Innocenti |first1=Fabrizio |last2=Robinson |first2=Rod |last3=Gardiner |first3=Tom |last4=Finlayson |first4=Andrew |last5=Connor |first5=Andy |date=2017 |title=Differential Absorption Lidar (DIAL) Measurements of Landfill Methane Emissions |journal=Remote Sensing |language=en |volume=9 |issue=9 |pages=953 |bibcode=2017RemS....9..953I |doi=10.3390/rs9090953 |doi-access=free|s2cid=6964229 }} Greenhouse gases are measured from space such as by the Orbiting Carbon Observatory and through networks of ground stations such as the Integrated Carbon Observation System.

The Annual Greenhouse Gas Index (AGGI) is defined by atmospheric scientists at NOAA as the ratio of total direct radiative forcing due to long-lived and well-mixed greenhouse gases for any year for which adequate global measurements exist, to that present in year 1990.{{cite web |author=LuAnn Dahlman |date=14 August 2020 |title=Climate change: annual greenhouse gas index |url=https://www.climate.gov/news-features/understanding-climate/climate-change-annual-greenhouse-gas-index |url-status=live |archive-url=https://web.archive.org/web/20130816013542/https://www.climate.gov/news-features/understanding-climate/climate-change-annual-greenhouse-gas-index |archive-date=16 August 2013 |access-date=5 September 2020 |publisher=NOAA Climate.gov science news & Information for a climate smart nation}} These radiative forcing levels are relative to those present in year 1750 (i.e. prior to the start of the industrial era). 1990 is chosen because it is the baseline year for the Kyoto Protocol, and is the publication year of the first IPCC Scientific Assessment of Climate Change. As such, NOAA states that the AGGI "measures the commitment that (global) society has already made to living in a changing climate. It is based on the highest quality atmospheric observations from sites around the world. Its uncertainty is very low."{{Cite web |title=The NOAA Annual Greenhouse Gas Index (AGGI) – An Introduction |url=https://www.esrl.noaa.gov/gmd/aggi/ |url-status=live |archive-url=https://web.archive.org/web/20201127013113/https://www.esrl.noaa.gov/gmd/aggi/ |archive-date=27 November 2020 |access-date=5 September 2020 |publisher=NOAA Global Monitoring Laboratory/Earth System Research Laboratories}}

{{excerpt|Carbon dioxide in Earth's atmosphere#Data networks|paragraphs=1}}

{{Further|Carbon cycle}}

The natural flows of carbon between the atmosphere, ocean, terrestrial ecosystems, and sediments are fairly balanced; so carbon levels would be roughly stable without human influence.{{cite book |last=Prentice |first=I.C. |title=Climate change 2001: the scientific basis: contribution of Working Group I to the Third Assessment Report of the Intergouvernmental Panel on Climate Change |year=2001 |editor1-last=Houghton |editor1-first=J.T. |chapter=The carbon cycle and atmospheric carbon dioxide |hdl=10067/381670151162165141}}{{cite web |year=2009 |title=An Introduction to the Global Carbon Cycle |url=http://globecarboncycle.unh.edu/CarbonCycleBackground.pdf |url-status=live |archive-url=https://web.archive.org/web/20161008110835/http://globecarboncycle.unh.edu/CarbonCycleBackground.pdf |archive-date=8 October 2016 |access-date=6 February 2016 |publisher=University of New Hampshire |df=dmy-all}} Carbon dioxide is removed from the atmosphere primarily through photosynthesis and enters the terrestrial and oceanic biospheres. Carbon dioxide also dissolves directly from the atmosphere into bodies of water (ocean, lakes, etc.), as well as dissolving in precipitation as raindrops fall through the atmosphere. When dissolved in water, carbon dioxide reacts with water molecules and forms carbonic acid, which contributes to ocean acidity. It can then be absorbed by rocks through weathering. It also can acidify other surfaces it touches or be washed into the ocean.{{Cite journal |title=Many Planets, One Earth // Section 4: Carbon Cycling and Earth's Climate |url=http://www.learner.org/courses/envsci/unit/text.php?unit=1&secNum=4 |url-status=live |journal=Many Planets, One Earth |volume=4 |archive-url=https://web.archive.org/web/20120417175417/http://www.learner.org/courses/envsci/unit/text.php?unit=1&secNum=4 |archive-date=17 April 2012 |access-date=2012-06-24 |df=dmy-all}}{{excerpt|Atmospheric carbon cycle|paragraphs=1}}

File:Greenhouse Gas Emissions by Economic Sector.svg

{{Main|Greenhouse gas emissions}}

The vast majority of carbon dioxide emissions by humans come from the burning of fossil fuels. Additional contributions come from cement manufacturing, fertilizer production, and changes in land use like deforestation.{{rp|687}}{{cite web |title=AR4 SYR Synthesis Report Summary for Policymakers – 2 Causes of change |url=https://www.ipcc.ch/publications_and_data/ar4/syr/en/spms2.html |url-status=dead |archive-url=https://web.archive.org/web/20180228235005/http://www.ipcc.ch/publications_and_data/ar4/syr/en/spms2.html |archive-date=28 February 2018 |access-date=9 October 2015 |work=ipcc.ch}} Methane emissions originate from agriculture, fossil fuel production, waste, and other sources. Rice paddies are a significant agricultural source of greenhouse gas emissions, contributing 22% of total agricultural methane and 11% of nitrous oxide emissions.{{Cite journal |last=Qian |first=Haoyu |last2=Zhu |first2=Xiangchen |last3=Huang |first3=Shan |last4=Linquist |first4=Bruce |last5=Kuzyakov |first5=Yakov |last6=Wassmann |first6=Reiner |last7=Minamikawa |first7=Kazunori |last8=Martinez-Eixarch |first8=Maite |last9=Yan |first9=Xiaoyuan |last10=Zhou |first10=Feng |last11=Sander |first11=Bjoern Ole |last12=Zhang |first12=Weijian |last13=Shang |first13=Ziyin |last14=Zou |first14=Jianwen |last15=Zheng |first15=Xunhua |date=October 2023 |title=Greenhouse gas emissions and mitigation in rice agriculture |url=https://www.nature.com/articles/s43017-023-00482-1 |journal=Nature Reviews Earth & Environment |language=en |volume=4 |issue=10 |pages=716–732 |doi=10.1038/s43017-023-00482-1 |issn=2662-138X|hdl=10871/134718 |hdl-access=free }}

If current emission rates continue then temperature rises will surpass {{convert|2.0|C-change}} sometime between 2040 and 2070, which is the level the United Nations' Intergovernmental Panel on Climate Change (IPCC) says is "dangerous".

Most greenhouse gases have both natural and human-caused sources. An exception are purely human-produced synthetic halocarbons which have no natural sources. During the pre-industrial Holocene, concentrations of existing gases were roughly constant, because the large natural sources and sinks roughly balanced. In the industrial era, human activities have added greenhouse gases to the atmosphere, mainly through the burning of fossil fuels and clearing of forests.{{cite web |year=2000 |title=Chapter 3, IPCC Special Report on Emissions Scenarios, 2000 |url=https://ipcc.ch/pdf/special-reports/spm/sres-en.pdf |url-status=live |archive-url=https://web.archive.org/web/20180820085208/http://www.ipcc.ch/pdf/special-reports/spm/sres-en.pdf |archive-date=20 August 2018 |access-date=2010-10-16 |publisher=Intergovernmental Panel on Climate Change}}{{rp|115}}{{Excerpt|Greenhouse gas emissions|Overview of main sources|only=paragraph|this=This section is|paragraphs=1-2}}

{{main|Climate change mitigation}}

{{Excerpt|Climate change mitigation|Needed emissions cuts}}

{{main|Carbon dioxide removal|Net-zero emissions|Carbon sink}}

Several technologies remove greenhouse gas emissions from the atmosphere. Most widely analyzed are those that remove carbon dioxide from the atmosphere, either to geologic formations such as bio-energy with carbon capture and storage and carbon dioxide air capture,{{cite web |year=2009 |title=Geoengineering the climate: science, governance and uncertainty |url=http://royalsociety.org/displaypagedoc.asp?id=35151 |url-status=dead |archive-url=https://web.archive.org/web/20090907031520/http://royalsociety.org/displaypagedoc.asp?id=35151 |archive-date=7 September 2009 |access-date=12 September 2009 |work=The Royal Society}} or to the soil as in the case with biochar. Many long-term climate scenario models require large-scale human-made negative emissions to avoid serious climate change.Fisher, B.S., N. Nakicenovic, K. Alfsen, J. Corfee Morlot, F. de la Chesnaye, J.-Ch. Hourcade, K. Jiang, M. Kainuma, E. La Rovere, A. Matysek, A. Rana, K. Riahi, R. Richels, S. Rose, D. van Vuuren, R. Warren, 2007: [https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg3-chapter3-1.pdf Chapter 3: Issues related to mitigation in the long term context], In [https://www.ipcc.ch/report/ar4/wg3/ Climate Change 2007: Mitigation. Contribution of Working Group III to the Fourth Assessment Report of the Inter-governmental Panel on Climate Change] [B. Metz, O.R. Davidson, P.R. Bosch, R. Dave, L.A. Meyer (eds)], Cambridge University Press, Cambridge,

Negative emissions approaches are also being studied for atmospheric methane, called atmospheric methane removal.{{Cite journal |last1=Jackson |first1=Robert B. |last2=Abernethy |first2=Sam |last3=Canadell |first3=Josep G. |last4=Cargnello |first4=Matteo |last5=Davis |first5=Steven J. |last6=Féron |first6=Sarah |last7=Fuss |first7=Sabine |last8=Heyer |first8=Alexander J. |last9=Hong |first9=Chaopeng |last10=Jones |first10=Chris D. |last11=Damon Matthews |first11=H. |last12=O'Connor |first12=Fiona M. |last13=Pisciotta |first13=Maxwell |last14=Rhoda |first14=Hannah M. |last15=de Richter |first15=Renaud |date=2021-11-15 |title=Atmospheric methane removal: a research agenda |journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |language=en |volume=379 |issue=2210 |pages=20200454 |bibcode=2021RSPTA.37900454J |doi=10.1098/rsta.2020.0454 |issn=1364-503X |pmc=8473948 |pmid=34565221}}

{{Further|History of climate change science|Greenhouse effect#History}}

File:19120814 Coal Consumption Affecting Climate - Rodney and Otamatea Times.jpg , March 1912, p. 341.]]

In the late 19th century, scientists experimentally discovered that {{chem|N|2}} and {{chem|O|2}} do not absorb infrared radiation (called, at that time, "dark radiation"), while water (both as true vapor and condensed in the form of microscopic droplets suspended in clouds) and {{CO2}} and other poly-atomic gaseous molecules do absorb infrared radiation.{{cite journal |last1=Arrhenius |first1=Svante |date=1896 |title=On the influence of carbonic acid in the air upon the temperature of the ground |url=http://www.rsc.org/images/Arrhenius1896_tcm18-173546.pdf |url-status=live |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science |volume=41 |issue=251 |pages=237–276 |doi=10.1080/14786449608620846 |archive-url=https://web.archive.org/web/20201118065555/https://www.rsc.org/images/Arrhenius1896_tcm18-173546.pdf |archive-date=18 November 2020 |access-date=1 December 2020}}{{cite journal |last1=Arrhenius |first1=Svante |year=1897 |title=On the Influence of Carbonic Acid in the Air Upon the Temperature of the Ground |journal=Publications of the Astronomical Society of the Pacific |volume=9 |issue=54 |pages=14 |bibcode=1897PASP....9...14A |doi=10.1086/121158 |doi-access=free}} In the early 20th century, researchers realized that greenhouse gases in the atmosphere made Earth's overall temperature higher than it would be without them. The term greenhouse was first applied to this phenomenon by Nils Gustaf Ekholm in 1901.{{cite web |last1=Easterbrook |first1=Steve |date=18 August 2015 |title=Who first coined the term "Greenhouse Effect"? |url=http://www.easterbrook.ca/steve/2015/08/who-first-coined-the-term-greenhouse-effect/ |url-status=live |archive-url=https://web.archive.org/web/20151113131713/http://www.easterbrook.ca/steve/2015/08/who-first-coined-the-term-greenhouse-effect/ |archive-date=13 November 2015 |access-date=11 November 2015 |website=Serendipity}}{{cite journal |author=Ekholm N |year=1901 |title=On The Variations Of The Climate Of The Geological And Historical Past And Their Causes |journal=Quarterly Journal of the Royal Meteorological Society |volume=27 |pages=1–62 |bibcode=1901QJRMS..27....1E |doi=10.1002/qj.49702711702 |number=117}}

During the late 20th century, a scientific consensus evolved that increasing concentrations of greenhouse gases in the atmosphere cause a substantial rise in global temperatures and changes to other parts of the climate system,{{Cite journal |last1=Cook |first1=J. |last2=Nuccitelli |first2=D. |last3=Green |first3=S.A. |last4=Richardson |first4=M. |last5=Winkler |first5=B.R. |last6=Painting |first6=R. |last7=Way |first7=R. |last8=Jacobs |first8=P. |last9=Skuce |first9=A. |year=2013 |title=Quantifying the consensus on anthropogenic global warming in the scientific literature |journal=Environmental Research Letters |volume=8 |issue=2 |page=024024 |bibcode=2013ERL.....8b4024C |doi=10.1088/1748-9326/8/2/024024 |doi-access=free}} with consequences for the environment and for human health.

{{Further|Greenhouse effect#Bodies other than Earth}}

Greenhouse gases exist in many atmospheres, creating greenhouse effects on Mars, Titan, and particularly in the thick atmosphere of Venus.{{cite web |author=Eddie Schwieterman |title=Comparing the Greenhouse Effect on Earth, Mars, Venus, and Titan: Present Day and through Time |url=http://www.astro.washington.edu/users/eschwiet/essays/greenhouse_ASTR555.pdf |url-status=dead |archive-url=https://web.archive.org/web/20150130202450/http://www.astro.washington.edu/users/eschwiet/essays/greenhouse_ASTR555.pdf |archive-date=30 January 2015}} While Venus has been described as the ultimate end state of runaway greenhouse effect, such a process would have virtually no chance of occurring from any increases in greenhouse gas concentrations caused by humans,{{cite report |url=https://www.ipcc.ch/site/assets/uploads/2018/03/inf3-6.pdf |title=Scoping of the IPCC 5th Assessment Report Cross Cutting Issues |work=Thirty-first Session of the IPCC Bali, 26–29 October 2009 |url-status=live |archive-url=https://web.archive.org/web/20091109215503/http://www.ipcc.ch/meetings/session31/inf3.pdf |archive-date=9 November 2009 |access-date=24 March 2019}} as the Sun's brightness is too low and it would likely need to increase by some tens of percents, which will take a few billion years.{{cite journal |last1=Hansen |first1=James |first2=Makiko |last2=Sato |first3=Gary |last3=Russell |first4=Pushker |last4=Kharecha |date=2013 |title=Climate sensitivity, sea level and atmospheric carbon dioxide |journal= Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |volume=371 |issue=2001 |at=20120294 |bibcode=2013RSPTA.37120294H |doi=10.1098/rsta.2012.0294 |pmid=24043864 |pmc=3785813|arxiv=1211.4846 }}

{{Portal|Climate change|Environment}}

• {{ Annotated link | Carbon accounting }}
• {{ Annotated link | Carbon budget }}
• {{ Annotated link | Carbon sequestration }}
• {{ Annotated link | Climate change feedbacks }}

{{Reflist}}

{{Wiktionary}}

• {{Commons category-inline}}
• {{citation |title=Carbon Dioxide Information Analysis Center (CDIAC) |publisher=U.S. Department of Energy |url=https://cdiac.ess-dive.lbl.gov/ |access-date=2020-07-26}}
• [http://www.cmdl.noaa.gov/aggi/ Annual Greenhouse Gas Index (AGGI)] from NOAA
• [http://www.spectralcalc.com/ Atmospheric spectra of GHGs and other trace gases]. {{Webarchive|url=https://web.archive.org/web/20130325100504/http://spectralcalc.com/ |date=25 March 2013 }}.

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