Ancient droughts offer clue to US Southwest's future

Monday 28th Feb 2011 by theWeather Club

New research, published last week in Nature, provides a fascinating insight into the climate of the American Southwest during the ancient Pleistocene period – and a chilling warning of what the future may hold for the region if man-made climate change continues unchecked.

A team of climate scientists at the University of New Mexico were able to produce a model of the region's climate history by using cutting edge techniques to analyse the geochemical profile of sediment from a dried-up lake in the Valles Caldera, New Mexico. The evidence they found suggested that phases of warmer climate during this period were marked by the abrupt arrival of megadroughts, which lasted for hundreds or even thousands of years and made the 1930s Dust Bowl period look positively verdant by comparison.

It is now feared that the Southwestern climate is set to switch to an extended dry mode similar to those that occurred during particularly warm Pleistocene periods. The temperatures experienced during these phases appear to have been similar to those currently being recorded in the region. The Southwest has experienced significant reductions in rainfall during the last decade, and climate models point to the region becoming even drier in the future as atmospheric circulation patterns change. According to the research team, a 10–15% reduction in rainfall would be enough to cause severe drought. The region's population grew rapidly throughout the 20th century – expanding by 1500% between 1900 and 1990 – meaning that the demand for water is greater than it has ever been. The Pleistocene droughts may be returning, but with far greater consequences.

"We won't know for sure if it happens again until we get there," says Fawcett, who led the research team. "But we are certainly increasing the possibility of crossing a critical threshold to severe and lasting drought conditions."