Contrails, those wispy clouds that form when ice crystals condense on jet engine vapors have been shown to raise and lower temperatures over large cities.

It was learned that contrails lower daytime and raise nighttime temperatures slightly in high-traffic jet corridors. Lacking those clouds for a few days after Sept. 11, the spread between daily high and low temperatures increased by about 2 degrees Fahrenheit.

There has been controversy over the global impact that jets have on the Earth’s atmosphere. Some of the comments in Upgrade: Travel Better’s post on the subject questioned if 3 days of data could really be conclusive. Those of you who’ve calculated the carbon impact of a recent vacation will find that air travel is where most of your carbon tonnage comes from.

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