Desert Southwest may be first U.S. victim of climate change – ‘Even the best-case scenario is not too good’

By Lauren Morello and Climatewire
December 14, 2010 A 60-year drought that scorched the Southwest during the 12th century may be a harbinger of things to come as greenhouse gases warm the Earth, according to research published yesterday in the Proceedings of the National Academy of Sciences. The study’s authors used tree rings to reconstruct a portrait of droughts that struck the Southwest over a 1,200-year period stretching back to 900 A.D. They believe that understanding the droughts of the past could help water managers plan for future dry periods that are expected to become more intense as climate change worsens. Portions of the Southwest have suffered prolonged drought since 2001. But the medieval drought, which peaked along the Colorado River between 1146 and 1155, stands as the worst drought in the region for at least 1,200 years, according to the tree ring records. Still, there are similarities to present-day conditions. The medieval drought occurred during a period from 900 to 1300 A.D. when the Southwest was about 1 degree Celsius warmer than average. Temperatures in the Southwest have been more than 1 degree Celsius warmer than average since 1990, and climate models suggest greater warming by the end of the century. … “Because climate warming will exacerbate water sustainability problems, the Southwest is likely to experience some of the highest economic expenses and environmental losses,” said Glen MacDonald, director of the University of California, Los Angeles’ Institute of the Environment, and an author of one of the new papers. “The ultimate costs of inaction in curbing greenhouse gas emissions will be particularly high for the Southwest.” Explosive population growth over the past century has pushed the Southwest’s relatively meager water supply to unsustainable levels of use, the PNAS studies conclude. The region’s population grew from 2.1 million to more than 50 million during the 20th century. The U.S. Census Bureau estimates that, by 2030, the Southwest will be home to more than 67 million people. Within 50 to 100 years, the current population could double. … “A lot of what we’re seeing is caused by natural variability,” said Richard Seager, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory. “There is this background steady drying of the region that is occurring due to rising greenhouse gases, and variability is moving around that.” … “In the worst-case scenario, it looks to me like models are going over more towards permanent drought-like conditions by the early part of the middle of this century,” Seager said. If an El Niño trend emerges, “it just takes longer to get there,” the scientist said of the drought. “They all get drier, so even the best-case scenario is not too good.”

Desert Southwest May Be First U.S. Victim of Climate Change