WASHINGTON (AP) — Last year’s huge drought was a freak of
nature that wasn’t caused by manmade global warming, according to a new federal
Scientists said the lack of moisture usually pushed up from
the Gulf of Mexico was the main reason for the drought in the American
The 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 — Colorado, Iowa, Kansas,
Missouri, Nebraska and Wyoming — but the drought spread much farther and
eventually included nearly two-thirds of the Lower 48 states.
For the six states, the drought was the worst four-month
period for lack of rainfall since records started being kept in 1895, Hoerling
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
Hoerling used computer simulations to see if he could
replicate the drought using manmade global warming conditions. He couldn’t, so
that means it was a random event, he said.
Using similar methods, Hoerling has been able to attribute
increasing droughts in the Mediterranean Sea region to climate change and found
that greenhouse gases could be linked to a small portion of the 2011 Texas heat
Another scientist blasted the report, though.
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 the how global warming exacerbated
the high pressure system that kept the jet stream north and the rainfall away,
“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.”
Hoerling noted that in the past 20 years, the world is
seeing more La Niñas, the occasional cooling of the central Pacific Ocean that
is the flip side of El Niño. He said that factor, not part of global warming,
but part of a natural cycle, increases the chances of such droughts.
Some regions should see more droughts as the world warms
because of greenhouse gases from the burning of fossil fuels such as coal, oil
and gas, he said. But the six-state area isn’t expected to get an increase of
droughts from global warming — unlike parts of the Southwest, Hoerling said.
Copyright 2013 Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.