The Once and Future Southwestern Mega-Drought

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Lately, I’ve stopped worrying about climate change. Wait, that’s not quite right. But I only have so much worry bandwidth, and what is keeping me up at night lately is scarcenomoics, the idea that in a finite world, we may be hitting limits on some natural resources. Climate change doesn’t even have to play a major role in these fears, though warming can be—as the Department of Defense guys like to call it—a threat multiplier. But even without warming, population growth and economic growth will put increasing pressure on food, water, soil, minerals and countless other natural resources that underpin our prosperity. Indeed, food prices are at a record high, and oil has risen past triple digits once again thanks to rising demand in the developing world and unrest in the Middle East. It’s possible that we’ll manage to innovate our way out of material limitations. We’ve always done so in the past, often by finding substitutes for scarce commodities. But there’s no getting around the fact that we live on a finite planet, and there are more of us (about 219,000) showing up every day.

That brings me to water and the American Southwest. Those states are already dry, and lately they’ve been getting drier. Las Vegas’s main reservoir at Lake Mead has fallen well below drought levels, California is fighting over water again and nationally, the picture looks like this, from the national drought monitor:

Water scarcity is the result of two factors: too little rain, and too many people needing water. Given that the Southwest is continuing to grow (people like hot and dry weather), the region is going to need more water—and more efficiency—if wants to escape being crippled by drought. But a new study in Nature raises the scary possibility that the Southwest can get much, much drier than it is now. A team of researchers led by Peter Fawcett, a climate scientist at the University of Albuquerque, reconstructed the Southwest’s climate history using data taken from an 82-meter-long lake sediment core from the Valles Caldera in New Mexico. They found that the region experienced a number of sudden and major climatic shifts during the Pleistocene Era, which ranged from 2.6 million to 12,000 years ago. During the warm periods in between glaciations, the Southwest suffered droughts that lasted for hundreds or even thousands of years These are droughts that would make the seven-year-long Dust Bowl of the 1930s look like a pleasant spring day.

Interestingly, as Quirin Schiermeier writes in Nature, is that if today’s climate ends up repeating the past, the Southwest might be entering a relatively cooler and wetter period. But we know the past won’t repeat itself—climate change is making sure of that. Manmade greenhouse gas emissions will almost certainly cause temperatures to rise in the future, which could tip the Southwest into a dry period likes of which we’ve never lived through before. As Fawcett told Schiermeier:

We won’t know for sure if it happens again until we get there. But we are certainly increasing the possibility of crossing a critical threshold to severe and lasting drought conditions… The scary thing is that we seem to be very close to this point again.

Indeed, previous studies have predicted that climate change will make the dry Southwest—and other already dry areas—that much drier, even as precipitation overall seems likely to increase. The point at which an extended dry period becomes a drought—and a long drought becomes a different climate—is a fine one. But it’s a point the Southwest is hurtling towards.

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