Editing Cirrus cloud (section)

=== Contrails ===
[[Contrail]]s are an [[anthropogenic cloud|artificial type]] of cirrus cloud formed when water vapor from the exhaust of a [[jet engine]] condenses on particles, which come from either the surrounding air or the exhaust itself, and freezes, leaving behind a visible trail. The exhaust can trigger the formation of cirrus by providing [[ice nuclei]] when there is an insufficient naturally-occurring supply in the atmosphere.<ref name="McGraw-2"/> One of the [[Environmental impact of aviation|environmental impacts of aviation]] is that persistent contrails can form into large mats of cirrus,<ref name="NASA-cirrus">{{cite web|url=http://www.nasa.gov/home/hqnews/2004/apr/HQ_04140_clouds_climate.html|publisher=[[National Aeronautics and Space Administration]]|title=Clouds Caused By Aircraft Exhaust May Warm The U.S. Climate|date=27 April 2004|first1=Gretchen|last1=Cook-Anderson|first2=Chris|last2=Rink|first3=Julia|last3=Cole|access-date=24 June 2011|archive-date=18 May 2011|archive-url=https://web.archive.org/web/20110518194600/http://www.nasa.gov/home/hqnews/2004/apr/HQ_04140_clouds_climate.html|url-status=live}}</ref> and increased air traffic has been implicated as one possible cause of the increasing frequency and amount of cirrus in Earth's atmosphere.<ref name="NASA-cirrus"/><ref name="Minnis-1671">{{harvnb|Minnis|Ayers|Palikonda|Phan|2004|p=1671}}</ref>
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