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Climate: Greenhouse gas buildup ‘loads the dice’ for Southwest megadroughts

Odds of 30-year dry spells increase dramatically as global temps rise

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Green bars indicate wet periods, the larger the bar the more unusually wet. In a similar way, yellow indicates dry and droughty periods. The graph stretches from January 1895 on the left to last month on the right, showing how the cycle of droughts alternating with wet years has changed, with dry years becoming more prevalent.

By Summit Voice

FRISCO — Tree ring records clearly show that the southwestern U.S. experienced megadroughts long before the anthropogenic global warming era. One such decades-long dry spell may have been a factor in the collapse of the Anasazi civilization at Mesa Verde.

But the steady buildup of heat-trapping gases in the atmosphere is loading the dice in favor of another megadrought sooner, rather later, according to scientists with Cornell University, the University of Arizona and U.S. Geological Survey. The chances of a decade-long drought is now at least 50 percent, and there’s a 20 percent to 50 percent chance of a 30-year megadrought.

“For the southwestern U.S., I’m not optimistic about avoiding real megadroughts,” said Toby Ault, Cornell assistant professor of earth and atmospheric sciences and lead author of the paper. “As we add greenhouse gases into the atmosphere – and we haven’t put the brakes on stopping this – we are weighting the dice for megadrought conditions.”

In fact, parts of the Southwest have been exceptionally dry throughout the first 14 years of this century, and current conditions in California may be a taste of the future.

According to Ault, climatologists don’t know whether the severe western and southwestern drought will continue, but he said, “With ongoing climate change, this is a glimpse of things to come. It’s a preview of our future.”

Ault said that the West and Southwest must look for mitigation strategies to cope with looming long-drought scenarios.

“This will be worse than anything seen during the last 2,000 years and would pose unprecedented challenges to water resources in the region,” he said.

The modeling by the researchers suggests California, Arizona and New Mexico will be especially vulnerable, whie the chances for drought in parts of Washington, Montana and Idaho may decrease.

Beyond the United States, southern Africa, Australia and the Amazon basin are also vulnerable to the possibility of a megadrought. With increases in temperatures, drought severity will likely worsen, the scientists concluded, adding that their findings “should be viewed as conservative.

“These results help us take the long view of future drought risk in the Southwest – and the picture is not pretty. We hope this opens up new discussions about how to best use and conserve the precious water that we have,” said Julia Cole, a University of Arizona professor of geosciences and of atmospheric sciences.

The study, “Assessing the Risk of Persistent Drought Using Climate Model Simulations and Paleoclimate Data,” will be published in the  American Meteorological Society’s Journal of Climate.

The National Science Foundation, National Center for Atmospheric Research, the U.S. Geological Survey and the National Oceanic and Atmospheric Administration funded the research.

 

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One Response

  1. Tree Rings? This chart is utter B.S. … Research historical droughts and you will find that the past has been more harsh than they are even predicting the future will be. This is disingenuous.

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