Do contrails change weather?
All photographs by Forrest M. Mims III, Copyright 1997. All rights reserved. Some contrails can last several hours or more and even spread out to form large cirrus clouds. Some regions have so much jet traffic that contrails can actually form an overcast which reduces sunlight. In November 1996 I measured reductions in sunlight caused by these contrails over Switzerland. There is evidence that masses of contrails can slightly reduce daytime temperatures by blocking sunlight. Contrails at night may slightly reduce cooling. While these effects may not affect the climate everywhere, some scientists believe contrails can have a noticeable effect on local weather.
