Abandoned boat in the recently dried bed of Lake Mead. Credit: Ethan Miller / Getty By Bryan Walsh
February 10, 2011 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. …

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