The drought in the American southwest is the worst in 12 centuries, and climate change is making it more likely to continue, according to research published in the journal Nature Climate Change.

“This drought at 22 years is still in full swing and it is very, very likely that this drought will survive to last 23 years,” A. Park Williams, a climate scientist at the University of California, Los Angeles, who led research on the current drought, told the New York Times.

Researchers analyzed tree rings to gauge water availability throughout history by focusing on parts of southern Montana to northern Mexico, and from the Pacific Ocean east to the Rocky Mountains.

Scientists can predict soil moisture in past climates by analyzing the thickness of tree rings, with wider rings indicating wetter years and thinner rings indicating drier years.

Research showed that, while droughts occur naturally over time, the extremity of the current drought has been influenced by human-induced climate change.

Williams said that extreme conditions in the summer of 2021 pushed the severity of the drought over the top. This resulted in 2000-2021 being the driest in a 22-year span since 800 A.D., which is the farthest statistics go back.

The study also found that there is a 75% chance that the current drought will last until at least 2030.