Editing Greenhouse effect (section)

== Bodies other than Earth ==
{| class="wikitable"
|+ Greenhouse effect on different celestial bodies<ref name="ACSplanet">{{cite web |title=Atmospheres and Planetary Temperatures |url=https://www.acs.org/climatescience/energybalance/planetarytemperatures.html |access-date=29 May 2023 |publisher=ACS |archive-date=27 January 2023 |archive-url=https://web.archive.org/web/20230127144936/https://www.acs.org/climatescience/energybalance/planetarytemperatures.html |url-status=dead }}</ref><ref name="McKay1991">{{Cite journal |last1=McKay |first1=C. P. |last2=Pollack |first2=J. B. |last3=Courtin |first3=R. |date=6 September 1991 |title=The greenhouse and antigreenhouse effects on Titan |url=https://wray.eas.gatech.edu/physicsplanets2012/Assignments/McKay_etal1991_TitanAntiGreenhouse.pdf |journal=Science |language=en |volume=253 |issue=5024 |pages=1118–1121 |bibcode=1991Sci...253.1118M |doi=10.1126/science.11538492 |issn=0036-8075 |pmid=11538492 |s2cid=10384331 |s2cid-access=free |url-status=live |archive-url=https://web.archive.org/web/20230629174917/https://wray.eas.gatech.edu/physicsplanets2012/Assignments/McKay_etal1991_TitanAntiGreenhouse.pdf |archive-date= 29 June 2023 }}</ref><ref name="nasatitan">{{cite web |title=Titan | date=2 May 2018 |url=https://solarsystem.nasa.gov/moons/saturn-moons/titan/in-depth/#:~:text=Titan%27s%20atmosphere%20is%20mostly%20nitrogen,accelerated%20in%20Saturn%27s%20magnetic%20field. |access-date=29 May 2023 |publisher=NASA}}</ref>
|-
! !!Venus !! Earth !! Mars !! Titan
|-
| Surface temperature, <math>T_\mathrm{observed}</math> || {{convert|735|K|C F|0|abbr=on}} || {{convert|288|K|C F|0|abbr=on}} ||{{convert|215|K|C F|0|abbr=on}} || {{convert|94|K|C F|0|abbr=on}}
|-
| Greenhouse effect, <math>\Delta T}_\mathrm{GHE</math>|| {{convert|503|K-change}} || {{convert|33|K-change}} || {{convert|6|K-change}} || {{convert|21|K-change}} GHE;<br />{{convert|12|K-change}} GHE+[[Anti-greenhouse effect|AGHE]]
|-
| Pressure || 92 atm || 1 atm || 0.0063 atm || 1.5 atm
|-
| Primary gases || {{CO2}} (0.965)<br /> N{{sub|2}} (0.035) || N{{sub|2}} (0.78)<br /> O{{sub|2}} (0.21)<br />Ar (0.009) || {{CO2}} (0.95)<br />N{{sub|2}} (0.03)<br />Ar (0.02) || N{{sub|2}} (0.95)<br /> {{CH4}} (≈0.05)
|-
| Trace gases || {{SO2}}, Ar || {{H2O-nl}}, {{CO2}} || O{{sub|2}}, CO || H{{sub|2}}
|-
| Planetary effective temperature, <math>T_\mathrm{eff}</math> || {{convert|232|K|C F|0|abbr=on}} || {{convert|255|K|C F|0|abbr=on}} || {{convert|209|K|C F|0|abbr=on}} || 73 K [[tropopause]];<br /> 82 K [[stratopause]]
|-
| Greenhouse effect, <math>G</math>|| {{Val|16000}} W/m{{sup|2}} || 150 W/m{{sup|2}} || 13 W/m{{sup|2}} || 2.8 W/m{{sup|2}} GHE;<br /> 1.9 W/m{{sup|2}} GHE+AGHE
|-
| Normalized greenhouse effect, <math>\tilde g</math>|| 0.99|| 0.39 || 0.11 || 0.63 GHE;<br /> 0.42 GHE+AGHE
|}

In the [[Solar System]], apart from the Earth, at least two other planets and a moon also have a greenhouse effect.

===Venus===
The greenhouse effect on [[Venus]] is particularly large, and it brings the surface temperature to as high as {{convert|735|K|C F|abbr=on}}. This is due to its very dense atmosphere which consists of about 97% carbon dioxide.<ref name="McKay1991"/>

Although Venus is about 30% closer to the Sun, it absorbs (and is warmed by) ''less sunlight'' than Earth, because Venus reflects 77% of incident sunlight while Earth reflects around 30%. In the absence of a greenhouse effect, the surface of Venus would be expected to have a temperature of {{Convert|232|K}}. Thus, contrary to what one might think, being nearer to the Sun is not a reason why Venus is warmer than Earth.<ref name="uwatmos211oct10">{{cite web |date=10 October 2001 |title=ATM S - Climate and Climate Change |url=https://atmos.washington.edu/academics/classes/2001Q4/211/notes_greenhouse.html |access-date=14 June 2023 |publisher=University of Washington}}</ref><ref>{{cite web |title=Venus Fact Sheet |url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/venusfact.html |access-date=25 April 2023 |website=NASA Space Science Data Coordinated Archive }}</ref><ref>{{cite web |title=5 Weird Facts About Venus |url=https://www.britannica.com/list/5-weird-facts-about-venus#:~:text=Even%20though%20Venus%20is%20much,and%20reradiated%20as%20infrared%20radiation. |access-date=25 April 2023 |publisher=Britannica}}</ref>

Due to its high pressure, the CO<sub>2</sub> in the atmosphere of Venus exhibits ''continuum absorption'' (absorption over a broad range of wavelengths) and is not limited to absorption within the bands relevant to its absorption on Earth.<ref name="Pierrehumbert2011" />

A [[runaway greenhouse effect]] involving carbon dioxide and water vapor has for many years been hypothesized to have occurred on [[Venus]];<ref>{{cite journal |last1=Rasool |first1=I. |last2=De Bergh |first2=C. |date=June 1970 |title=The Runaway Greenhouse and the Accumulation of CO<sub>2</sub> in the Venus Atmosphere |url=http://pubs.giss.nasa.gov/docs/1970/1970_Rasool_DeBergh.pdf |url-status=dead |journal=Nature |volume=226 |issue=5250 |pages=1037–9 |bibcode=1970Natur.226.1037R |doi=10.1038/2261037a0 |pmid=16057644 |s2cid=4201521 |archive-url=https://web.archive.org/web/20111021110413/http://pubs.giss.nasa.gov/docs/1970/1970_Rasool_DeBergh.pdf |archive-date=21 October 2011}}</ref> this idea is still largely accepted.<ref name="McCarthy">{{Cite web |last=McCarthy |first=Michael Cabbage and Leslie |title=NASA climate modeling suggests Venus may have been habitable |url=https://climate.nasa.gov/news/2475/nasa-climate-modeling-suggests-venus-may-have-been-habitable |url-status=live |archive-url=https://web.archive.org/web/20210811030814/https://climate.nasa.gov/news/2475/nasa-climate-modeling-suggests-venus-may-have-been-habitable/ |archive-date=11 August 2021 |access-date=11 August 2021 |website=Climate Change: Vital Signs of the Planet|date=10 August 2016 }}</ref> The planet [[Venus (planet)|Venus]] experienced a runaway greenhouse effect, resulting in an atmosphere which is 96% [[carbon dioxide]], and a surface [[atmospheric pressure]] roughly the same as found {{convert|900|m|ft|abbr=on}} underwater on Earth. Venus may have had water oceans, but they would have boiled off as the mean surface temperature rose to the current {{convert|735|K|C F|abbr=on}}.<ref>{{cite journal |author=Hashimoto, G. L. |author2=Roos-Serote, M. |author3=Sugita, S. |author4=Gilmore, M. S. |author5=Kamp, L. W. |author6=Carlson, R. W. |author7=Baines, K. H. |date=2008 |title=Felsic highland crust on Venus suggested by Galileo Near-Infrared Mapping Spectrometer data |journal=[[Journal of Geophysical Research: Planets]] |volume=113 |issue=E9 |pages=E00B24 |bibcode=2008JGRE..113.0B24H |doi=10.1029/2008JE003134 |s2cid=45474562 |doi-access=free}}</ref><ref>{{cite web |author=David Shiga |date=10 October 2007 |title=Did Venus's ancient oceans incubate life? |url=https://www.newscientist.com/article/dn12769-did-venuss-ancient-oceans-incubate-life.html |url-status=live |archive-url=https://web.archive.org/web/20090324134332/https://www.newscientist.com/article/dn12769-did-venuss-ancient-oceans-incubate-life.html |archive-date=24 March 2009 |access-date=17 July 2019 |work=New Scientist}}</ref><ref name="Jakosky">{{cite book |last1=Jakosky |first1=Bruce M. |title=The New Solar System |date=1999 |publisher=Sky Publishing |isbn=978-0-933346-86-4 |editor1-last=Beatty |editor1-first=J. Kelly |edition=4th |location=Boston |pages=175–200 |chapter=Atmospheres of the Terrestrial Planets |oclc=39464951 |editor2-last=Petersen |editor2-first=Carolyn Collins |editor3-last=Chaikin |editor3-first=Andrew}}</ref>

===Mars===
[[Mars]] has about 70 times as much carbon dioxide as Earth,<ref name="Crisp2012">{{cite web |last1=Crisp |first1=D. |date=2012 |title={{CO2}} GREENHOUSE EFFECTS ON VENUS, EARTH, AND MARS |url=https://www.lpi.usra.edu/meetings/climatology2012/pdf/8083.pdf |access-date=28 May 2023 |publisher=Jet Propulsion Laboratory, California Institute of Technology}}</ref> but experiences only a small greenhouse effect, about {{convert|6|K-change}}.<ref name="ACSplanet" /> The greenhouse effect is small due to the lack of water vapor and the overall thinness of the atmosphere.<ref>{{cite web |last1=Brennan |first1=John |date=2017 |title=Does Mars Have a Greenhouse Effect? |url=https://sciencing.com/mars-greenhouse-effect-1914.html |website=Sciencing}}</ref>

The same radiative transfer calculations that predict warming on Earth accurately explain the temperature on Mars, given its atmospheric composition.<ref>{{cite web |title=Does the {{CO2}} atmosphere of Mars disprove greenhouse warming? |url=https://metafact.io/factchecks/77-does-the-co2-atmosphere-of-mars-disprove-greenhouse-warming |access-date=28 May 2023 |website=metafact}}</ref><ref name="WeartVenus">{{cite web |last1=Weart |first1=Spencer |title=The Discovery of Global Warming: Venus & Mars |url=https://history.aip.org/climate/Venus.htm |access-date=29 May 2023 |website=Center for History of Physics |publisher=American Institute of Physics}}</ref><ref name="Haberle2013" />

===Titan===
[[Saturn]]'s moon [[Titan (moon)|Titan]] has both a greenhouse effect and an [[anti-greenhouse effect]]. The presence of nitrogen ([[Dinitrogen|N<sub>2</sub>]]), methane ([[CH4|CH<sub>4</sub>]]), and hydrogen ([[Hydrogen|H<sub>2</sub>]]) in the atmosphere contribute to a greenhouse effect, increasing the surface temperature by {{convert|21|K-change}} over the expected temperature of the body without these gases.<ref name="McKay1991" /><ref name="astrobio2005">{{Cite web |date=3 November 2005 |title=Titan: Greenhouse and Anti-greenhouse |url=https://www.astrobio.net/retrospections/titan-greenhouse-and-anti-greenhouse/ |url-status=usurped |archive-url=https://web.archive.org/web/20190927031140/https://www.astrobio.net/retrospections/titan-greenhouse-and-anti-greenhouse/ |archive-date=27 September 2019 |access-date=4 November 2019 |website=Astrobiology Magazine |language=en-US}}</ref>

While the gases N<sub>2</sub> and H<sub>2</sub> ordinarily do not absorb infrared radiation, these gases absorb thermal radiation on Titan due to pressure-induced collisions, the large mass and thickness of the atmosphere, and the long wavelengths of the thermal radiation from the cold surface.<ref name="Pierrehumbert2011" /><ref name="McKay1991" /><ref name="astrobio2005" />

The existence of a high-altitude haze, which absorbs wavelengths of solar radiation but is transparent to infrared, contribute to an anti-greenhouse effect of approximately {{convert|9|K-change}}.<ref name="McKay1991" /><ref name="astrobio2005" />

The net result of these two effects is a warming of 21 K − 9 K = {{convert|12|K-change}}, so Titan's surface temperature of {{convert|94|K|C F|0|abbr=on}} is 12 K warmer than it would be if there were no atmosphere.<ref name="McKay1991" /><ref name="astrobio2005" />

=== Effect of pressure ===
The relative sizes of the greenhouse effects on different bodies cannot be predicted simply by comparing the amount of greenhouse gases in their atmospheres. This is because factors other than the quantity of these gases also play a role in determining the size of the greenhouse effect.

Overall atmospheric pressure affects how much thermal radiation each molecule of a greenhouse gas can absorb. High pressure leads to more absorption and low pressure leads to less.<ref name="Pierrehumbert2011" />

This is due to "pressure broadening" of [[spectral lines]]. When the total atmospheric pressure is higher, collisions between molecules occur at a higher rate. Collisions broaden the width of absorption lines, allowing a greenhouse gas to absorb thermal radiation over a broader range of wavelengths.<ref name="PierrehumbertTextbook" />{{rp|226}}

Each molecule in the air near Earth's surface experiences about 7 billion collisions per second. This rate is lower at higher altitudes, where the pressure and temperature are both lower.<ref name="eiuatmo">{{cite web |title=The Atmosphere |url=https://www.ux1.eiu.edu/~cfjps/1400/atmos_struct.html#:~:text=Near%20sea%20level%2C%20an%20atom,is%20about%201%20each%20minute. |access-date=30 May 2023 |website=Eastern Illinois University}}</ref> This means that greenhouse gases are able to absorb more wavelengths in the lower atmosphere than they can in the upper atmosphere.<ref name="Plass1950" /><ref name="Wallace2006" />

On other planets, pressure broadening means that each molecule of a greenhouse gas is more effective at trapping thermal radiation if the total atmospheric pressure is high (as on Venus), and less effective at trapping thermal radiation if the atmospheric pressure is low (as on Mars).<ref name="Pierrehumbert2011" />