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They also found that during the years 2000 through 2002, almost a third of all contrail outbreaks were in the Midwest. Next in line were the Northeast and Southeast, each with a fifth of the overall U.S. contrail action. Western states have contrail outbreaks as well, but not so many, Carleton told Discovery News. Contrails form a layer of high clouds that seem to cool things off during the day. However, that effect is deceptive. It turns out that the clouds also reduce the temperature difference between night and day by trapping "long-wave radiation" -- which means heat -- and not letting it escape into outer space. "They tend to heat the upper troposphere more than they warm the surface," explained Patrick Minnis of NASA's Langley Research Center. "The debate now is whether the warming is larger than the albedo." In other words, do the white contrails reflect more sunlight energy than they trap? Most researchers lean towards the heat-trapping effect being greater. But the jury is still out. The good news is that even if the contrails turn out to contribute to local heating and global warming, it's fairly easy to avoid making contrails by simply having plane avoid the air that is most likely to form the cloud -- or to fly in natural cirrus clouds that are already there, said Minnis. To make that possible, he and his team are already working on a contrail forecasting tool. Related Links: Larry O'Hanlon's blog: Earth Impacts NASA's Langley Research Center How Stuff Works: Why do those long, white clouds form behind jets flying high overhead? |
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