Global warming may change Southwest climate

WASHINGTON — 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.

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

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 says, 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 by the Intergovernmental Panel on Climate Change, the international scientific effort to assess the impact of global warming, which released a new report Friday. The drought results were analyzed separately in a paper published on-line 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 the authors of the new paper had a very high level of confidence that the droughts will develop and that they will be the result of increases in atmospheric greenhouse gases created through burning fossil fuels and other human activities.

The researchers said future 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 Nino and La Nina ocean temperature variations. The Southwest has seen significantly below-average rainfall since 1999, and there is some preliminary information to suggest that global warming is already playing a role the current drought.