The dry regions of the subtropics are on the move. Using satellite data gathered over the last 25 years, researchers at the University of Washington have been able to determine that the jet streams - a pattern of westerly winds that help drive weather in both hemispheres - have shifted about 70 miles toward their respective poles over the study period. The dry subtropical climate regions, which of course contain some of the world's major deserts, could encroach into temperate regions. Areas such as the Mediterranean, southern Europe and the northern part of the Middle East could end up having a tendency toward more drought.
U.S. satellite data since 1979 has revealed that the troposphere--the weather-bearing layer of our atmosphere that extends more than seven miles up--warmed the most, by roughly 1.5 degrees Fahrenheit, in the middle latitudes. This band of warming crosses the southern U.S. as well as southern China and North Africa in the Northern Hemisphere and southern Australia, South Africa and lower South America in the Southern Hemisphere. This warmer air expands the reach of the tropics and pushes the jet streams toward the poles. "We estimate that the jet streams in both hemispheres have shifted poleward by roughly 1 degree latitude in both summer and winter seasons," the researchers, led by Qiang Fu of the University of Washington, write in today's Science. Each degree of latitude represents roughly 70 miles.
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