“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.”
Researchers claim the region’s 19-year drought, from 2000–2018, already rivals that of any over the past 1,200 years.
“We’re no longer looking at projections, but at where we are now,” said lead author Park Williams, a bio-climatologist at Columbia University’s Lamont-Doherty Earth Observatory, in a statement. “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.”
For the study, published in the journal Science, Williams and the other researchers looked at nine U.S. states, stretching from Oregon and Montana at the northern and southward through California and New Mexico. The researchers also included a portion of northern Mexico in the study.
Using tree ring data to infer yearly soil moisture and plot out the pre-modern data, the researchers documented four mega-droughts—multi-decade droughts—beginning in 800 AD.
The southwest’s current drought was worse compared to the ones that took place in the late 800s, mid-1100s, and the 1200s. The most severe mega-drought on record began in 1575, though researchers said the difference between that Medieval one and the current was slight.
And while natural variability played a role in the current drought, the scientists estimate about half the blame—47 percent—lies with the Earth’s heating, as warmer air is able to suck up more ground moisture.
According to coauthor Benjamin Cook of Lamont and the Goddard Institute for Space Studies, “It doesn’t matter if this is exactly the worst drought ever” but that “it has been made much worse than it would have been because of climate change.”
“Because the background is getting warmer, the dice are increasingly loaded toward longer and more severe droughts,” added Williams.
“We may get lucky, and natural variability will bring more precipitation for a while,” he said. “But going forward, we’ll need more and more good luck to break out of drought, and less and less bad luck to go back into drought.”
Andrea Germanos is a staff writer at Common Dreams.