Robinson Meyer reports:

Every so often, the American West seems to lurch into something called a “mega-drought.” The rains falter, the rivers wither, and the forests become tinder boxes waiting for a spark. Mega-droughts are notoriously hard to study—the last one happened in the 16th century—but what we do know is worrisome. In the 1540s, a few wet years in the middle of a mega-drought may have triggered one of the worst disease epidemics ever recorded.

According to research unveiled last week, mega-droughts may no longer be history. On Thursday, a team of climate scientists argued that the American West may currently be experiencing its first mega-drought in more than 500 years. A record-breaking period of aridity set in around the year 2000 and continues to this day, they said.

“The last 19 years have been equivalent to the worst 19 years of the worst mega-droughts on record,” said Park Williams, a professor of bioclimatology at Columbia University, at a presentation of the work. Only three recent mega-droughts—in the late 800s, the mid-1100s, and the late 1500s—were worse than the current period, he added.

Climate change seems to be driving a good chunk of the problem. “The current drought is substantially worse than it would have been without global warming,” Williams said. The drought was 62 percent more severe than it would have been, he said, due to human-caused climate change. [Continue reading…]