Editing Cirrus cloud (section)

== Effects on climate ==
Cirrus clouds cover up to 25% of the Earth (up to 70% in the tropics at night<ref>{{harvnb|Lolli|Campbell|Lewis|Gu|2017|loc=Section 3}}</ref>) and have a net heating effect.<ref name="Nucleation">{{harvnb|Franks|2003|pp=557–574}}</ref> When they are thin and translucent, the clouds efficiently absorb outgoing [[infrared]] radiation while only marginally reflecting the incoming sunlight.<ref name="stephens-1742">{{harvnb|Stephens|Tsay|Stackhouse|Flatau|1990|p=1742}}</ref> When cirrus clouds are {{convert|100|m|ft|abbr=on}} thick, they reflect only around 9% of the incoming sunlight, but they prevent almost 50% of the outgoing infrared radiation from escaping, thus raising the temperature of the atmosphere beneath the clouds by an average of 10&nbsp;°C (18&nbsp;°F)<ref name="liou-1191">{{harvnb|Liou|1986|p=1191}}</ref>—a process known as the [[greenhouse effect]].<ref name="earthobs-global-warming">{{cite web|url=http://earthobservatory.nasa.gov/Features/GlobalWarming/|publisher=National Aeronautics and Space Administration|title=Global Warming: Feature Articles|access-date=16 October 2012|work=Earth Observatory|date=3 June 2010|archive-date=5 May 2020|archive-url=https://web.archive.org/web/20200505194248/https://earthobservatory.nasa.gov/features/GlobalWarming|url-status=live}}</ref> Averaged worldwide, cloud formation results in a temperature loss of 5&nbsp;°C (9&nbsp;°F) at the earth's surface, mainly the result of [[stratocumulus cloud]]s.<ref name="cloud-heating">{{cite web|url=http://isccp.giss.nasa.gov/role.html|title=Cloud Climatology|work=International Satellite Cloud Climatology Program|publisher=National Aeronautics and Space Administration|access-date=12 July 2011|archive-date=30 January 2020|archive-url=https://web.archive.org/web/20200130020610/https://isccp.giss.nasa.gov/role.html|url-status=live}}</ref>

Cirrus clouds are likely becoming more common due to [[climate change]]. As their greenhouse effect is stronger than their reflection of sunlight, this would act as a [[climate change feedback|self-reinforcing feedback]].{{Sfn|Forster|Storelvmo|Armour|Collins|2021|loc=7:66, Section 7.4.2.4.2}} [[Air pollution|Metallic particles from human sources]] act as additional nucleation seeds, potentially increasing cirrus cloud cover and thus contributing further to climate change.<ref name="cirrus-origins" /> Aircraft in the upper troposphere can create [[contrail|contrail cirrus clouds]] if local weather conditions are right. These contrails contribute to climate change.<ref>{{Cite journal|last=Kärcher|first=Bernd|date=2018|title=Formation and radiative forcing of contrail cirrus|journal=Nature Communications|language=en|volume=9|issue=1|page=1824|doi=10.1038/s41467-018-04068-0|pmid=29739923 |pmc=5940853 |bibcode=2018NatCo...9.1824K |issn=2041-1723}}</ref>

[[Cirrus cloud thinning]] has been proposed as a possible [[geoengineering]] approach to reduce climate damage due to [[carbon dioxide]]. Cirrus cloud thinning would involve injecting particles into the upper troposphere to reduce the amount of cirrus clouds. The [[IPCC Sixth Assessment Report|2021 IPCC Assessment Report]] expressed low confidence in the cooling effect of cirrus cloud thinning, due to limited understanding.{{sfn|Lee|Marotzke|Bala|Cao|2021|loc=4:89, Section 4.6.3.3}}