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solonavi 14 February 2007 Climate, General, Global Warming 105 views No Comment Print This Post  Email This Post

sciencedaily

NASA scientists may have discovered how a warmer climate in the future could increase droughts in certain parts of the world, including the southwest United States.

The researchers compared historical records of the climate impact of changes in the sun’s output with model projections of how a warmer climate driven by greenhouse gases would change rainfall patterns. They found that a warmer future climate likely will produce droughts in the same areas as those observed in ancient times, but potentially with greater severity.

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Using the NASA Goddard Institute for Space Studies climate model, researchers found that changes in solar output in the ancient past increased surface warming and altered atmospheric moisture and circulations. These changes likely led to the severe droughts seen in paleoclimate records.

The same model showed that greenhouse-gas warming has similar effects on the atmosphere, suggesting drier conditions may become more common in the subtropics. Rainfall could decrease further in already water-stressed regions such as the southwest United States, Mexico, parts of North Africa, the Middle East, and Australia. Meanwhile, precipitation may increase across the western Pacific, along much of the equator and in parts of southeast Asia.

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Researchers also considered numerous tree-ring, fire, and lake sediment records from across the Americas, including Mexico, Peru, and the Yucatan Peninsula. These data are reliable indicators of historical climate and confirm a pronounced increase in drought frequency in the southern United States, Mexico, and other subtropical locations during periods of increased solar output in the past 1,200 years. This long-term record of solar output is based on chemical isotopes whose production is related to the sun’s brightness. Conversely, in parts of the tropics, ocean sediment data, key indicators of precipitation changes, reflect increased rainfall.

According to the researchers, the same processes identified by this new research very likely also affected past civilizations, such as the Pueblo people of New Mexico and Arizona who abandoned cities in the 1300s.

Typically arid regions of the world, such as the U.S. Southwest, may become even drier in the future, according to new results from NASA climate models. This still image is taken from an animation that shows observations of average rainfall from 1998 through 2000 from the Tropical Rainfall Measuring Mission satellite. Red and yellow indicate areas of high rainfall. Blue and green depict areas of low rainfall. (Credit: TRMM/NASA/JAXA)