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Earth's deserts are expanding, a study says

WASHINGTON -- Deserts in the American Southwest and around the globe are creeping toward heavily populated areas as the jet streams shift, researchers reported yesterday.

The result: Areas already stressed by drought may get even drier.

Satellite measurements made from 1979 to 2005 show that the atmosphere in the subtropical regions both north and south of the equator is heating up. As the atmosphere warms, warmer air bulges out at the altitudes where the northern and southern jet streams slip past. That bulging has pushed both jet streams about 70 miles closer to the Earth's poles.

Because the jet streams mark the edge of the tropics, their outward movement has allowed the tropics to grow wider by about 140 miles. That means the relatively drier subtropics move as well, pushing closer to places like Salt Lake City, where Thomas Reichler, coauthor of the study in the journal Science, teaches meteorology.

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