The white, cloudy contrails airplanes often leave in the sky may be full of ice crystals, but they're warming the globe, according to a new study. By flying in the wake of various aircraft—ranging in size from the 47-metric-ton Airbus A319 to the 508-metric-ton Airbus A380 (contrails of two Airbus A340s shown)—and analyzing their less-than-10-minute-old contrails, researchers have found that fresh contrails tend to trap outbound infrared radiation, slightly heating Earth. Based on 2005 air traffic figures such contrails, if their effect were to be evenly spread out across the globe, would continuously trap 15.9 milliwatts of power per square meter, the researchers report this month in Geophysical Research Letters. That's about 1% of the amount trapped by the carbon dioxide added to the atmosphere since the beginning of the Industrial Revolution.
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