April 12, 2013 in Nation/World

Study: Climate change did not cause drought

Seth Borenstein Associated Press
 

WASHINGTON – Last year’s huge drought was a freak of nature that wasn’t caused by man-made global warming, a new federal science study finds.

Scientists say the lack of moisture usually pushed up from the Gulf of Mexico was the main reason for the drought in the nation’s midsection.

Thursday’s report by dozens of scientists from five different federal agencies looked into why forecasters didn’t see the drought coming. The researchers concluded that it was so unusual and unpredictable that it couldn’t have been forecast.

“This is one of those events that comes along once every couple hundreds of years,” said lead author Martin Hoerling, a research meteorologist at the National Oceanic and Atmospheric Administration. “Climate change was not a significant part, if any, of the event.”

Researchers focused on six states – Wyoming, Kansas, Nebraska, Colorado, Missouri and Iowa – but the drought spread much farther and eventually included nearly two-thirds of the Lower 48 states.

He said the jet stream that draws moisture north from the Gulf was stuck unusually north in Canada.

Other scientists have linked recent changes in the jet stream to shrinking Arctic sea ice, but Hoerling and study co-author Richard Seager of Columbia University said those global warming connections are not valid.

Another scientist though, blasted the report.

Kevin Trenberth, climate analysis chief at the National Center for Atmospheric Research, a federally funded university-run research center, said the report didn’t take into account the lack of snowfall in the Rockies the previous winter and how that affected overall moisture in the air. Nor did the study look at how global warming exacerbated the high pressure system that kept the jet stream north and the rainfall away, he said.

“This was natural variability exacerbated by global warming,” Trenberth said in an email. “That is true of all such events from the Russian heat wave of 2010, to the drought and heat waves in Australia.”

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