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Carbon dioxide: A trace gaseous component of the atmosphere whose concentration is increasing. In 1860, its concentration was 288 parts per million (ppm); in 1980, 332 ppm; in 2007, 383 ppm.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
