A very good article in the Washington Post lays out the problem we face.

“Global warming will intensify drought, and it will intensify floods,” explains Stephen Schneider, editor of the journal Climatic Change and a lead author for the authoritative Intergovernmental Panel on Climate Change (IPCC). Why?

As the air gets warmer, there will be more water in the atmosphere. That’s settled science … You are going to intensify the hydrologic cycle. Where the atmosphere is configured to have high pressure and droughts, global warming will mean long, dry periods. Where the atmosphere is configured to be wet, you will get more rain, more gully washers.

The droughts will be especially bad. How bad?

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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.

Droughts and water shortages already been driving conflict around the globe:

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.

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We still have time to avert devastating drought in the Southwest — and worsening water wars around the globe — in the second half of the century. But only if we act now to begin sharply reducing greenhouse-gas emissions.

This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.