Google Earth:
"NASA scientists have found that cirrus clouds, formed by contrails from aircraft engine exhaust, are capable of increasing average surface temperatures enough to account for a warming trend in the United States that occurred between 1975 and 1994. According to Patrick Minnis, a senior research scientist at NASA’s Langley Research Center in Hampton, Va., there has been a one percent per decade increase in cirrus cloud cover over the United States, likely due to air traffic. Cirrus clouds exert a warming influence on the surface by allowing most of the Sun’s rays to pass through but then trapping some of the resulting heat emitted by the surface and lower atmosphere. Using a general circulation model, Minnis estimates that cirrus clouds from contrails increased the temperatures of the lower atmosphere by anywhere from 0.36 to 0.54°F per decade. Minnis’s results show good agreement with weather service data, which reveal that the temperature of the surface and lower atmosphere rose by almost 0.5°F per decade between 1975 and 1994."
