NASA scientists say they may have discovered how a warmer climate in the future could cause more drought in certain parts of the world, including the Southwest United States. They 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.
The researchers note that the findings show how greenhouse gases and long-term changes in solar activity both can have major influences on climate by similar processes. They note changes are already evident in rainfall patterns in the Mediterranean area, North Africa and the Middle East. If those pattern changes continue it could pose significant water resource challenges to large segments of the population.
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.