Climate: A New Study Finds That Global Warming Could Dry Out the Southwest

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Lake Mead. Credit: Ethan Miller/Getty

It’s not the heat that might get us with climate change—it’s the humidity, so to speak. The risk of sea level rise due to melting land ice is one of the most recognized—if controversial and hard to predict—threats posed by global warming. Other potential impacts from global warming include increasingly powerful storms and floods of the sort that have ravaged Australia this past month and a half (while recognizing scientists can’t yet fingerprint individual weather events as caused by warming).

But as climate change create havoc from too much water, parts of the world could end up suffering from too little water. That’s the conclusion of a new study released today by the Stockholm Environment Institute (SEI), an environmental research organization based, unsurprisingly, in Stockholm (Download a PDF of the report here.) The report found that the already dry states of the American Southwest—Arizona, California, Nevada, New Mexico and Utah—will face a major water shortfall over the next century just based on population and income growth alone. (The region has long been one of the fastest-growing in the U.S., in part because of the hot and dry weather.) But climate change could make the situation much, much worse. According to the SEI study, global warming could increase the long-term water shortfall by a quarter, adding an additional 282 million to 439 million acre feet of water to the 1.815 billion acre feet shortfall already expected. Based on the price of adding reservoir capacity in California, meeting the baseline water shortage could cost $2.3 trillion—yes, that’s “trillion” with a “t”—plus $353 billion to $549 billion if climate change is factored in. Higher water prices would make adaptation even more expensive—assuming additional water could be found at all in a drier future. As Frank Ackerman, the director of the Climate Economics Group at SEI-U.S. and a co-author of the study, said in a statement:

Climate change is affecting Americans in many areas; the water crisis in the Southwest is one of the clearest examples. Climate policy choices we make today are not just about exotic environments and far-future generations – they will help determine how easy or hard it is to create a sustainable water system in the most arid region of the country.

As the report points out, water shortages in the Southwest aren’t anything new, and so far we’ve managed to adapt to a dry climate even as cities like Las Vegas and Phoenix essentially rise out of the desert. But even before climate change has really become a factor, water supplies have already dropped to scary levels throughout the region. Water levels at Lake Mead, the manmade reservoir that feeds Las Vegas, have fallen drastically in recent months, while California has endured a three year-long drought that only recently has shown signs of ending. The Southwest has been accustomed to unlimited growth in cities and exurbs along with unlimited water for irrigated agriculture, but the day may come soon when a choice will have to be made between the city and the farm. I visited Lake Mead myself in 2008, and even then, the falling water levels did not bode well for the future of Las Vegas and the rest of the Southwest:

Through air that shimmers in the blast furnace of a July day, you can see how far Mead’s water level has fallen. White bathtub rings of mineral deposits, measuring high-water marks that grow less high every year, circle the edges of the reservoir. Today Mead’s water level is 1,108 ft., down from more than 1,200 ft. in 2000. (The official drought level is 1,125 ft.) If the water continues to decline, says marine geophysicist Tim Barnett of the Scripps Institution of Oceanography, “buckle up.” Barnett co-authored a study estimating a 50% chance that a combination of climate change and increased demand could render Mead effectively dry by 2021. [Las Vegas water manager Pat] Mulroy doubts Barnett’s dire conclusion, but she knows Las Vegas–and the world beyond–faces an existential crisis over water. “This is about being able to survive as a human being,” she says. (See pictures of the world water crisis.)

Lake Mead’s level is currently at 1,093 ft.—below the official drought point.

Even scarier might be the impact of climate drying on agriculture. Food prices are already at a record high—thanks to extreme weather events, rising demand in developing nations and likely some speculation—but in the decades to come farmers will need to feed billions more, many of them wealthier and demanding more meat. (One lb. of animal protein can require 100 lbs. of grain to produce, and thousands of gallons of water.) 70% of the world’s freshwater is used for irrigation, so when we talk about water-related climate problems, we’re really talking about farming. Even more worrying, agriculture in much of the world has already been propped up by groundwater pumped from aquafiers—but half the planet lives in areas where water tables are  falling due to overdepletion. According to the World Bank, 15% of India’s food supply is grown with water produced by aquafiers—and they don’t recharge quickly. “That means 175 million people in India are being supported by food grown with groundwater,” says Lester Brown, the founder of the Earth Policy Institute and a long-time pessimist on farming and climate. In China, that figure could be as high as 130 million.

What happens if agriculture begins to wilt and food prices rise? Governments can fall—as Egypt’s nervous government knows, where high food prices have been one factor in that country’s unprecedented mass protests. Other Middle Eastern countries—already under stress by the combined effect that population growth and climate change may be having on local agriculture—are rightfully worried that they could be next. “You could see governments falling left and right, food riots and instability on a scale we have not seen before,” says Brown. “Desperate people do desperate things.”

I doubt you’re likely to see the sunburned citizens of San Diego or Reno take to the streets any time soon over the price of bread. The U.S., after all, should have no trouble feeding itself—even though over 50 million Americans live in food insecure households,  that has more to do with structural problems than lack of production. But an ever drier Southwest is one that truly will face an existential threat in the decades ahead—and the rest of us might not be far behind.

More from TIME on water and climate:

Dying for a Drink

World Water Crisis