Scientists say a 20-year drought across the western US is in fact an emerging "megadrought" as bad as any in the region over the last 1,200 years. Megadroughts, intense droughts that last decades, have a long history in the Desert Southwest. Indeed, the study area—including nine states from Oregon and Montana south to California and New Mexico—has seen four since the year 800. But "we now have enough observations of current drought and tree-ring records of past drought to say that we're on the same trajectory as the worst prehistoric droughts," Columbia University bioclimatologist A. Park Williams says, per USA Today. This drought, which has states battling wildfires while reservoirs are depleting, is "bigger than what modern society has seen."
Williams and his team attribute 47% of the drought to man-made global warming, per the AP. "Because the background is getting warmer, the dice are increasingly loaded toward longer and more severe droughts," Williams says in a release. In fact, he says it's possible the area could stay dry for centuries, as was the case with a megadrought beginning in the 1200s, though "that's not my prediction right now." Another troubling sign: Tree rings show that the 20th century, when most of the more than 70 million current residents moved in, was the wettest in the 1,200-year period. This "gave us an overly optimistic view of how much water is potentially available," says study co-author Benjamin Cook, whose research was published Thursday in Science. (Read more megadrought stories.)