Chemistry:Greenhouse gas

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Short description: Heat-trapping gas in an atmosphere

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Greenhouse gases trap some of the heat that results when sunlight heats the Earth's surface. Three important greenhouse gases are shown symbolically in this image: carbon dioxide, water vapor, and methane.
Physical drivers of global warming that has happened so far. Future global warming potential for long-lived drivers like carbon dioxide emissions is not represented. Whiskers on each bar show the possible error range.

Greenhouse gases (GHGs) are the gases in an atmosphere that trap heat, raising the surface temperature of astronomical bodies such as Earth. Unlike other gases, greenhouse gases absorb the radiations that a planet emits, resulting in the greenhouse effect.[1] The Earth is warmed by sunlight, causing its surface to radiate heat, which is then mostly absorbed by greenhouse gases. Without greenhouse gases in the atmosphere, the average temperature of Earth's surface would be about −18 °C (0 °F),[2] rather than the present average of 15 °C (59 °F).[3][4] Human-induced warming has been increasing at an unprecedented rate since it has started being measured, reaching 0.27±0.1 °C per decade over 2015–2024. This high rate of warming is caused by a combination of greenhouse gas emissions being at an all-time high of 53.6±5.2 Gt CO2e per year over the last decade (2014–2023), as well as reductions in the strength of aerosol cooling.[5]

The five most abundant greenhouse gases in Earth's atmosphere, listed in decreasing order of average global mole fraction, are:[6][7] water vapor, carbon dioxide, methane, nitrous oxide, ozone. Other greenhouse gases of concern include chlorofluorocarbons (CFCs and HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons, SF6, and NF3. Water vapor causes about half of the greenhouse effect, acting in response to other gases as a climate change feedback.[8]

Human activities since the beginning of the Industrial Revolution (around 1750) have increased carbon dioxide by over 50%,[9] and methane levels by 150%.[10] Carbon dioxide emissions are causing about three-quarters of global warming, while methane emissions cause most of the rest.[11] The vast majority of carbon dioxide emissions by humans come from the burning of fossil fuels,[12] with remaining contributions from agriculture and industry.[13]: 687  Methane emissions originate from agriculture, fossil fuel production, waste, and other sources.[14] The carbon cycle takes thousands of years to fully absorb CO
2 from the atmosphere,[15] while methane lasts in the atmosphere for an average of only 12 years.[16]

Natural flows of carbon happen between the atmosphere, terrestrial ecosystems, the ocean, and sediments. These flows have been fairly balanced over the past one million years,[17] although greenhouse gas levels have varied widely in the more distant past. Carbon dioxide levels are now higher than they have been for three million years.[18] The 2023 annual update of key indicators reveals that human-induced temperature rise, greenhouse gas concentrations, and the Earth's energy imbalance have all reached new records.[19] If current emission rates continue, then global warming will surpass 2.0 °C (3.6 °F) sometime between 2040 and 2070. This is a level which the Intergovernmental Panel on Climate Change (IPCC) says is "dangerous".[20]


Properties and mechanisms

refer to caption and adjacent text
Atmospheric absorption and scattering at different wavelengths 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.[21]: 2233 

99% of the Earth's dry atmosphere (excluding water vapor) is made up of nitrogen (N2) (78%) and oxygen (O2) (21%). Because their molecules contain two atoms of the same element, they have no asymmetry in the distribution of their electrical charges,[22] and so are almost totally unaffected by infrared thermal radiation,[23] with only an extremely minor effect from collision-induced absorption.[24][25][26] 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.[22]

Radiative forcing

Main article: Astronomy:Radiative forcing
Hansen et al. (2025) wrote that the IPCC had underestimated aerosols' cooling effect, causing it to also underestimate climate sensitivity (Earth's responsiveness to increases in greenhouse gas concentrations).[27] 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.[27]
Longwave-infrared 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.[28] 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.[21]: 2245 [29]

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.[30]: 139 [31] 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.[32]

  1. ↑ Matthews, J.B.R. et al. (2021-08-09). "Annex VII: Glossary". Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC / Cambridge University Press. pp. 2215–2256. doi:10.1017/9781009157896.022. ISBN 978-1-009-15789-6. https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf. 
  2. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named NASACO2
  3. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named Trenberth2003
  4. ↑ Le Treut, H., R. Somerville, U. Cubasch, Y. Ding, C. Mauritzen, A. Mokssit, T. Peterson and M. Prather, 2007: "Chapter 1: Historical Overview of Climate Change". In: "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.
  5. ↑ Forster, Piers (2025). "Indicators of Global Climate Change 2024: annual update of key indicators of the state of the climate system and human influence". Journal Earth System Science Data 17 (6): 2641–2680. doi:10.5194/essd-17-2641-2025. Bibcode: 2025ESSD...17.2641F. https://essd.copernicus.org/articles/17/2641/2025/. 
  6. ↑ "Atmospheric Concentration of Greenhouse Gases". U.S. Environmental Protection Agency. 2016-08-01. https://www.epa.gov/sites/default/files/2016-08/documents/print_ghg-concentrations-2016.pdf. 
  7. ↑ "Inside the Earth's invisible blanket.". http://sequestration.org/science/greenhousegases.html. 
  8. ↑ Gavin Schmidt (2010-10-01). "Taking the Measure of the Greenhouse Effect". NASA Goddard Institute for Space Studies – Science Briefs. https://www.giss.nasa.gov/research/briefs/2010_schmidt_05/. 
  9. ↑ "Carbon dioxide now more than 50% higher than pre-industrial levels" (in en). National Oceanic and Atmospheric Administration. 3 June 2022. https://www.noaa.gov/news-release/carbon-dioxide-now-more-than-50-higher-than-pre-industrial-levels. 
  10. ↑ "Understanding methane emissions". International Energy Agency. https://www.iea.org/reports/global-methane-tracker-2023/understanding-methane-emissions. "The concentration of methane in the atmosphere is currently over two-and-a-half times greater than its pre-industrial levels" 
  11. ↑ "Global Greenhouse Gas Emissions Data". United States Environmental Protection Agency. 12 January 2016. https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data. 
  12. ↑ "Global Greenhouse Gas Emissions Data". U.S. Environmental Protection Agency. 12 January 2016. https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data. "The burning of coal, natural gas, and oil for electricity and heat is the largest single source of global greenhouse gas emissions." 
  13. ↑ Canadell, J.G., P.M.S. Monteiro, M.H. Costa, L. Cotrim da Cunha, P.M. Cox, A.V. Eliseev, S. Henson, M. Ishii, S. Jaccard, C. Koven, A. Lohila, P.K. Patra, S. Piao, J. Rogelj, S. Syampungani, S. Zaehle, and K. Zickfeld, 2021: Chapter 5: Global Carbon and other Biogeochemical Cycles and Feedbacks. In 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. 673–816, doi:10.1017/9781009157896.007.
  14. ↑ "Global Methane Tracker 2023". International Energy Agency. 21 February 2023. https://www.iea.org/reports/global-methane-tracker-2023. 
  15. ↑ "Climate Change Indicators: Greenhouse Gases". United States Environmental Protection Agency. 16 December 2015. https://www.epa.gov/climate-indicators/greenhouse-gases. "Carbon dioxide's lifetime cannot be represented with a single value because the gas is not destroyed over time, but instead moves among different parts of the ocean–atmosphere–land system. Some of the excess carbon dioxide is absorbed quickly (for example, by the ocean surface), but some will remain in the atmosphere for thousands of years, due in part to the very slow process by which carbon is transferred to ocean sediments." 
  16. ↑ "Understanding methane emissions". International Energy Agency. https://www.iea.org/reports/global-methane-tracker-2023/understanding-methane-emissions. 
  17. ↑ "Climate Change Indicators: Atmospheric Concentrations of Greenhouse Gases". U.S. Environmental Protection Agency. 27 June 2016. https://www.epa.gov/climate-indicators/climate-change-indicators-atmospheric-concentrations-greenhouse-gases. 
  18. ↑ Lindsey, Rebecca. "Climate Change: Atmospheric Carbon Dioxide". https://www.climate.gov/news-features/understanding-climate/climate-change-atmospheric-carbon-dioxide. 
  19. ↑ Forster, Piers M.; Smith, Chris; Walsh, Tristram; Lamb, William F.; Lamboll, Robin; Hall, Bradley; Hauser, Mathias; Ribes, Aurélien et al. (2024-06-05). "Indicators of Global Climate Change 2023: annual update of key indicators of the state of the climate system and human influence" (in en). Earth System Science Data 16 (6): 2625–2658. doi:10.5194/essd-16-2625-2024. ISSN 1866-3516. Bibcode: 2024ESSD...16.2625F. https://essd.copernicus.org/articles/16/2625/2024/. 
  20. ↑ "Analysis: When might the world exceed 1.5C and 2C of global warming?" (in en). 2020-12-04. https://www.carbonbrief.org/analysis-when-might-the-world-exceed-1-5c-and-2c-of-global-warming. 
  21. ↑ 21.0 21.1 IPCC, 2021: 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 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.
  22. ↑ 22.0 22.1 Archer, David (2011). Global Warming: Understanding the Forecast, Chapter 4: Greenhouse Gases (2 ed.). Wiley. ISBN 978-0-470-94341-0. http://forecast.uchicago.edu/chapter4.pdf. Retrieved 14 June 2023. 
  23. ↑ Wei, Peng-Sheng; Hsieh, Yin-Chih; Chiu, Hsuan-Han; Yen, Da-Lun; Lee, Chieh; Tsai, Yi-Cheng; Ting, Te-Chuan (6 October 2018). "Absorption coefficient of carbon dioxide across atmospheric troposphere layer". Heliyon 4 (10). doi:10.1016/j.heliyon.2018.e00785. ISSN 2405-8440. PMID 30302408. Bibcode: 2018Heliy...400785W. 
  24. ↑ Höpfner, M.; Milz, M.; Buehler, S.; Orphall, J.; Stiller, G. (24 May 2012). "The natural greenhouse effect of atmospheric oxygen (O2) and nitrogen (N2)" (in en). Geophysical Research Letters 39 (L10706). doi:10.1029/2012GL051409. ISSN 1944-8007. Bibcode: 2012GeoRL..3910706H. 
  25. ↑ "Which Gases Are Greenhouse Gases?". American Chemical Society. https://www.acs.org/content/acs/en/climatescience/greenhousegases/whichgases.html. 
  26. ↑ Höpfner, M.; Milz, M.; Buehler, S.; Orphall, J.; Stiller, G. (24 May 2012). "The natural greenhouse effect of atmospheric oxygen (O2) and nitrogen (N2)" (in en). Geophysical Research Letters 39 (L10706). doi:10.1029/2012GL051409. ISSN 1944-8007. Bibcode: 2012GeoRL..3910706H. 
  27. ↑ 27.0 27.1 Hansen, James E.; Kharecha, Pushker; Sato, Makiko; Tselioudis, George et al. (3 February 2025). "Global Warming Has Accelerated: Are the United Nations and the Public Well-Informed?". Environment 67 (1): 6–44. doi:10.1080/00139157.2025.2434494. Bibcode: 2025ESPSD..67....6H.  Figure 3.
  28. ↑ "Climate Change Indicators in the United States – Greenhouse Gases". U.S. Environmental Protection Agency (EPA). 2016. https://www.epa.gov/climate-indicators/greenhouse-gases. .
  29. ↑ "Climate Change Indicators in the United States – Climate Forcing". U.S. Environmental Protection Agency (EPA). 2016. https://www.epa.gov/climate-indicators/climate-change-indicators-climate-forcing. [1]
  30. ↑ Wallace, J. M.; Hobbs, P. V. (2006). Atmospheric Science (2 ed.). Academic Press. ISBN 978-0-12-732951-2. 
  31. ↑ Manabe, S.; Strickler, R. F. (1964). "Thermal Equilibrium of the Atmosphere with a Convective Adjustment". J. Atmos. Sci. 21 (4): 361–385. doi:10.1175/1520-0469(1964)021<0361:TEOTAW>2.0.CO;2. Bibcode: 1964JAtS...21..361M. 
  32. ↑ Hatfield, Miles (30 June 2021). "NASA Satellites See Upper Atmosphere Cooling and Contracting Due to Climate Change". NASA. https://www.nasa.gov/general/nasa-satellites-see-upper-atmosphere-cooling-and-contracting-due-to-climate-change/. 
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