The megadrought in the American West is the worst in at least 1200 years, according to a recent study by UCLA researchers, and human-led climate change is a key part of it.

Park Williams, a climate hydrologist at UCLA, has been studying the history of soil hydration from California to Texas, Oregon to the Mexican border for several years. He measures modern moisture levels, and looks at the rings of tree to form educated estimates going back to the year 800, which is about as far back as trees can tell us.

The megadrought in the area is considered to have begun in 2002, one of the driest years ever according to William’s research. It continued unbroken until 2018, seemed to peter out with a wet 2019, and then came roaring back in 2020 and 2021. 2021 tied with 2002 for dryness, second only to 1580.

According to the trees, there has only been one comparable drought in the West, in the 1500s, and the current megadrought has already lasted longer and is as much as 5 percent drier. While the end of the drought is an inevitability, we don’t know when it will happen, and Williams’ research indicates there will be a gap of only a few years before another one begins, instead of centuries.

Williams used 29 climate models to compare actual conditions to hypothetical conditions without human-caused elements like atmospheric change. According to his modeling, 42 percent of the current drought conditions are due to human-caused warming, while 58 percent are due to natural climate variation. Without climate change, he said, this megadrought would have ended in 2005 or 2006 when humid conditions, if the air were a degree colder, would have broken the drought.

The study “is an important wake-up call,” said Jonathan Overpeck, dean of environment at the University of Michigan, who wasn’t part of the study. “Climate change is literally baking the water supply and forests of the Southwest, and it could get a whole lot worse if we don’t halt climate change soon.”

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