California's current drought ranks as "exceptionally severe" by historical standards—perhaps the worst such event in 1,200 years. But it's nothing compared to what could be coming if we don't stem climate change, according to new research. Without action to curb carbon emissions, the Southwest faces a high risk of multi-decade "megadrought" this century.
The research, led by climate scientist Toby Ault at Cornell University, parses the likelihood of the Southwest facing a drought lasting 35 years or more—the definition of a megadrought. If temperatures rise four degrees above pre-industrial levels—the worse-case scenario for global warming this century—prolonged drought is a near-certainty. At lower temperatures, and with greater rainfall, the risk level falls to between 20% and 50%.
"Megadroughts are rare events, occurring only once or twice each millennium. In earlier work, we showed that climate change boosts the chances of a megadrought, but in this paper we investigated how cutting fossil fuel emissions reduces this risk," Ault says.
The research shows that keeping temperature increases below 2 degrees Celsius—the threshold level set by international climate agreements—reduces the risk of megadrought to below 66%, given most predicted rainfall patterns. For that to happen, our reliance on fossil fuels needs to be cut drastically.
The Southwest can also reduce its risk by making better use of water. By keeping moisture in the ground—through efficiency strategies, water transfers, and more surface irrigation—the likelihood of drought falls below 50%. But cutting emissions and reducing temperatures is easier than saving water, the paper says.
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