Climate change could result in a so-called ‘mega-drought’ in the US, scientists war. Lasting for decades, the consequences would be worse than previous droughts. But the catastrophe can still be averted. John Dyer reports from Boston.
The US is facing the prospect of a mega-drought. Less rain and snow combined with scorching temperatures could parch the American Southwest and Great Plains starting in around 2050, scientists claim.
Drought lasting for decades
“The droughts that people do know about like the 1930s ‘dustbowl’ or the 1950s drought or even the ongoing drought in California and the Southwest today – these are all naturally occurring droughts that are expected to last only a few years or perhaps a decade,” said Ben Cook of the NASA’s Goddard Institute for Space Studies, who co-authored the study in the journal Science Advances. “Imagine instead the current California drought going on for another 20 years,” said Cook.
The drought in California began four years ago and has placed enormous strain on the state’s water reserves, affecting Los Angeles residents as well as farmers in the agricultural Central Valley.
Worse than previous droughts
Cook published his study with Cornell University Geoscientist Toby Ault and Columbia University Climatologist Jason Smerdon in the journal Science Now. On Thursday they spoke to journalists at the American Association for the Advancement of Science conference in San José, California.
The researchers based their study on soil moisture and other measurements, including the size of tree rings – which are thicker in wetter years thicker – and concluded there was an 80 per cent chance of a 35-year-long drought occurring before the end of the century in North America.
The drought would resemble or even exceed the so-called Medieval Climate Anomaly of the 12th and 13th centuries when precipitation plummeted and temperatures skyrocketed in a region stretching from the Canadian border to Texas. These mega-droughts lasted for up to 50 years, said Cook. “And they were droughts that no-one in the history of the United States has ever experienced.”
But the currently predicted drought would have far worse consequences that the Medieval anomaly, the scientists said in their study, because of the fast growth of large cities like Albuquerque, Dallas, Los Angeles, Las Vegas, Oklahoma City and Phoenix in recent years.
“Human populations in this region, and their associated water resource demands, have been increasing rapidly in recent decades, and these trends are expected to continue for years to come,” the scientists write in their paper.
Catastrophe can be averted
The study’s co-authors nonetheless believe that humans can work to avert the terrible drought if they curb carbon emissions, step up conservation, improve urban planning and take other measures to address climate change.
“We’re not necessarily locked into these high levels of mega-drought risk if we take actions to slow the effects of rising greenhouse gases on global temperatures,” said co-author Toby Ault. After all, the region recovered from the Medieval anomaly.
“The records we have of past mega-droughts are based on tree-ring width estimates, and if you think that through, that’s a little bit encouraging because it means the events weren’t so bad as to kill off all the trees,” added Ault. “I am optimistic that we can cope with the threat of mega-drought in the future because it doesn’t mean no water, it just means significantly less water than we’re used to.”
Choice between electricity or water
Geoscientist Kevin Anchukaitis of the Woods Hole Oceanographic Institution in Massachusetts predicts that the study’s findings will lead to major disagreements among politicians on how to respond to the threat, especially as the US has dammed major rivers in the west to generate electricity. Knocking down those dams to alleviate a mega-drought would create other problems.
“In the not-too-distant future, the impending droughts will put a lot more pressure on all our resources,” he said. “We can head off some of the impact by reducing greenhouse gas emissions, but we’ll face difficult choices about reducing our hydropower capacity.”