They’re called contrails – short for condensation trails. These long, thin manmade clouds are formed by jet exhaust and can stretch for miles behind aircraft at cruising altitude.
Contrails usually form above 26,000 feet, where the temperature is -40 degrees.
When conditions are right, the sky can be laced with contrail lines. “We’re able to study individual contrails and how they form in different conditions and track them for a long time without interference from other contrails,” said Dr. Patrick Minnis of NASA.
For the first time since the jet age began, commercial aircraft were grounded following September 11 – allowing NASA scientists to study isolated contrails formed by a handful of military aircraft.
Their analysis showed that contrails spread out forming cirrus-like clouds lasting seven hours on average. “We had speculated for a long time that jet contrails are potentially contributing enough to the overall high cloud amount to allow a suppression of temperatures during the daytime and an increase in temperature at night,” explains David Travis of the University of Wisconsin.
And analysis confirmed a link — from September 11 to the 14 – the absence of contrails did alter air temperatures. “Temperature range during those three days was unusually large. That being, the days were slightly warmer and the nights were slightly colder than the 30 year average,” said Travis.
Follow up studies indicate that averaged out over time, contrails have a net warming on temperatures – especially from night flights that account for 25 percent of daily air traffic. And with the air travel expected to double, even triple over the next 50 years, these man made clouds will eventually play an even bigger role in our climate puzzle.
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