The megadrought bedeviling the American West got even drier last year and is becoming the deepest dry spell in more than 1,200 years.
Monday's study says the megadrought is now the worst-case scenario officials and scientists worried about in the 1900s.
The drought deepened so much in 2021 that it is 5% worse than the old record in the late 1500s.
Scientists compare this megadrought to what would happen in a hypothetical world without human-caused climate change.
And they calculate that 42% of this drought is due to global warming from the burning of fossil fuels.