Global Warming May Transform Southwest United States Into Dustbowl

Global warming will permanently change the climate of the American Southwest, making it so much hotter and drier that Dust Bowl-scale droughts will become common, a new climate report concludes.

Much of the nation west of the Mississippi River is likely to get drier because of the buildup of greenhouse gases in the atmosphere, but the greatest effect will be felt in already arid areas on both sides of the U.S.-Mexico border. By the end of the century, the climate researchers predict, annual rainfall in that region will have decline by a worrisome 10 to 20 percent.

A similar drying-out of the "subtropical" belt above and below the equator will hit the Mediterranean region and parts of Africa, South America and South Asia, the report said, as the overall warming of the oceans and surface air transforms basic wind and precipitation patterns around the Earth.

The prediction of a drier Southwest was made by 16 of 19 climate computer models assembled for the Intergovernmental Panel on Climate Change, the international scientific effort to assess the impact of global warming, which is releasing a new report today. The drought results were analyzed separately in a paper published online yesterday by the journal Science, which also predicted that regions outside the drying belt will get more rain.

"It's a situation of the poor getting poorer and the rich getting richer when it comes to rainfall," said Yochanan Kushnir of the Lamont-Doherty Earth Observatory of Columbia University, one of the paper's authors. "From a climate perspective, these changes are quite dramatic."

He said that the paper's authors have a high level of confidence that droughts will develop, and that they will result from increases in atmospheric greenhouse gases created through burning fossil fuels and other human activities.

The researchers said droughts in the affected regions will be different from those in the past, which were caused by local weather conditions and the effects of El Ni?o and La Ni?a ocean-temperature variations. The Southwest has had significantly below-average rainfall since 1999, and preliminary information suggests that global warming is already playing a role in the current drought.

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