"What is unusual is that after the La Niña ended in 2002, the drought persisted with only brief interruptions," Seager said.
The new paper suggests that the ongoing aridity is linked to broader changes that are causing the drier regions of the subtropics to expand toward the poles—a likely consequence of global warming.
Kenneth Cole is a climate researcher with the U.S. Geological Survey's Southwestern Biological Science Center, who was not a co-author on the new study.
He acknowledges that the paper relies solely on computer models to reach its conclusions about the impacts of climate change.
"One could take a skeptical stance that it is not really possible to model something so complex as climate in a computer," he said.
But Cole isn't skeptical about the latest results.
"The fact that only 1 of the 19 climate models reviewed did not show drier conditions over the next century is alarming," he said. "These types of comparisons rarely show that much of a consensus."
Furthermore, he said, the models match what he and other researchers in the Southwest have been documenting for a decade.
Continued drought in the Southwest is likely to reduce freshwater supplies and increase wildfire potential, the experts note.
(Related: "Warming Climate Fueling Wildfires, Study Says" [July 6, 2006].)
In addition, plants and the animals that depend on them will likely migrate to higher elevations. Species that can't migrate quickly enough won't survive.
Thomas Whitham, who directs the Merriam-Powell Center for Environmental Research at Northern Arizona University, hopes the new study will serve as a wake-up call to residents of the Southwest.
"If we continue to draw down water to maintain our lifestyle with its exorbitant use of water," he said, "we can effectively turn a hundred-year drought into a millennium-level drought, which far worsens the community and ecosystem consequences."
And because this is a global trend, the U.S. won't be the only country affected.
For USGS's Cole, the new paper also suggests "a spread of global drought into many of the [developing] countries least prepared to deal with it."
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