Folks in much of the American West are suffering through their 5th year of drought. It may get worse. Scientists led by Columbia University's Earth Institute say the Western states may be particularly prone to drought during periods of warming climate.

Using tree ring data and other indicators of ancient climate change, the researchers studied cycles of aridity in the western U.S. over the past 1,200 years. They found a 400-year period of dry weather and extended drought in the West from AD 900 to 1300. That corresponded with the "Medieval Warm Period" which saw unusual warmth in much of the Northern Hemisphere. Their conclusion, to be published in the journal Science: "Any trend towards warmer temperatures in the future could lead to a serious long-term increase in aridity over Western North America."

Co-author David Meko, of the University of Arizona, said the lengthening drought in the West today "pales in comparison with some of the earlier droughts we see from the tree-ring record. What would really put a stress on society is decade-long drought." And that possibility becomes a potential reality in a world increasingly affected by greenhouse warming, the study said.

Maybe this is why Ted Turner has become Nebraska's largest landowner. Those vast tracts provide grazing for Turner's buffalo. But they also stand atop one of the world's richest deposits of groundwater - the Ogallala aquifer. Smart.