Warming Will Exacerbate Global Water Conflicts

These will not be small droughts. Richard Seager, a senior researcher at Lamont-Doherty Earth Observatory of Columbia University, looked at 19 computer models of the future under current global warming trends. He found remarkable consistency: Sometime before 2050, the models predicted, the Southwest will be gripped in a dry spell akin to the Great Dust Bowl drought that lasted through most of the 1930s.

The spacing of tree rings suggests there have been numerous periods of drought going back to A.D. 800, he said. But, "mechanistically, this is different. These projections clearly come from a warming forced by rising greenhouse gases."

Farmers in the Central Valley, where a quilt of lush, green orchards on brown hills displays the alchemy of irrigation, want to believe this is a passing dry spell. They thought a wet 2006 ended a seven-year drought, but this year is one of the driest on record. For the first time, state water authorities shut off irrigation pumps to large parts of the valley, forcing farmers to dig wells.

Farther south and east, the once-mighty Colorado River is looking sickly, siphoned by seven states before dribbling into Mexico. Its reservoirs, Lake Mead and Lake Powell, are drying, leaving accusatory rings on the shorelines and imperiling river-rafting companies.

Seager predicts that drought will prompt dislocations similar to those of the Dust Bowl. "It will certainly cause movements of people. For example, as Mexico dries out, there will be migration from rural areas to cities and then the U.S.," he said. "There is an emerging situation of climate refugees."

Global warming threatens water supplies in other ways. Much of the world's fresh water is in glaciers atop mountains. They act as mammoth storehouses. In wet or cold seasons, the glaciers grow with snow. In dry and hot seasons, the edges slowly melt, gently feeding streams and rivers. Farms below are dependent on that meltwater; huge cities have grown up on the belief the mountains will always give them drinking water; hydroelectric dams rely on the flow to generate power.

But the atmosphere's temperature is rising fastest at high altitudes. The glaciers are melting, initially increasing the runoff, but gradually getting smaller and smaller. Soon, many will disappear.

At the edge of the Quelccaya Glacier, the largest ice cap in the Peruvian Andes, Ohio State University researcher Lonnie Thompson sat in a cold tent at a rarified 17,000 feet. He has spent more time in the oxygen-thin "death zone" atop mountains than any other scientist, drilling ice cores and measuring glaciers. He has watched the Quelccaya Glacier shrink by 30 percent in 33 years.

Down the mountain, a multitude of rivulets seep from the edge of Quelccaya to irrigate crops of maize, the water flowing through irrigation canals built by the Incas. Even farther downstream, the runoff helps feed the giant capital, Lima, another city built in a desert.

"What do you think is going to happen when this stops?" Thompson mused of the water. "Do you think all the people below will just sit there? No. It's crazy to think they won't go anywhere. And what do you think will happen when they go to places where people already live?"

The potential for conflict is more than theoretical. Turkey, Syria and Iraq bristle over the Euphrates and Tigris rivers. Sudan, Ethiopia and Egypt trade threats over the Nile. The United Nations has said water scarcity is behind the bloody wars in Sudan's Darfur region. In Somalia, drought has spawned warlords and armies.

Already, the World Health Organization says, 1 billion people lack access to potable water. In northern China, retreating glaciers and shrinking wetlands that feed the Yangtze River prompted researchers to warn that water supplies for hundreds of millions of people may be at risk.