September 11, 2001

As soon as officials recognized that terrorists had hijacked at least four, possibly more, planes on the morning of September 11, 2001, all commercial air traffic was grounded in the U.S. for three days. The situation provided atmospheric scientists with the unique opportunity to study how the exhaust from all those airplanes affects the weather.

Climatologists David Travis of the University of Wisconsin at Whitewater and Andrew Carleton of Pennsylvania State University looked at the average daily temperature range for September 11- 13, 2001, and compared that to the average daily temperature range for the same days in September over the last 30 years.The researchers found that the temperature range was about 2 degrees Fahrenheit greater while the planes were grounded.

The scientists hypothesize that the jet exhaust-or contrails- act like artificial clouds, simultaneously blocking incoming solar energy and trapping the heat radiating off the planet's surface. In this way, jet contrails keep the Earth cooler during the day and warmer during the nights. Although the jet contrails' affect is regional and not global, the research is one more example of how human activity can alter weather patterns.

For more info see also:
Discover article entitled "Climate on the Wing."
http://www.discover.com/aug_02/breakclimate.html

JET AIRCRAFT CONTRAILS: SURFACE TEMPERATURE VARIATIONS DURING THE AIRCRAFT GROUNDINGS OF SEPTEMBER 11-13, 2001
http://academics.uww.edu/geography/
Proceedings%20Paper.doc

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