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2011 Texas drought was 20 times more likely due to warming, study says

The National Oceanographic and Atmospheric Administration issued a warning that previously unusual weather is now becoming more and more common, in part due to the changes occurring at the two poles of the Earth. NBC's Anne Thompson reports.

Trying to get beyond the standard scientific disclaimer that no single weather event can be pinned on global warming, government scientists on Tuesday unveiled a new framework: what are the odds of a specific event being impacted by warming?

They tested it on several extreme events in 2011 -- a strong La Nina year -- and, in the case of the record Texas drought, concluded that such severe dry spells are 20 more times likely during a La Nina year today than a La Nina in the 1960s, before greenhouse gas emissions jumped. 

"Conditions leading to droughts such as the one that occurred in Texas in 2011 are, at least in the case of temperature, distinctly more probable than they were 40-50 years ago," researchers concluded in a new study.

"It's quite striking," Peter Stott told reporters Tuesday at a briefing organized by his employer, Britain's weather service, and the U.S. National Climatic Data Center.

"We can now quantify the changed odds" due to climate change and thus start to assess risk levels, added Stott, who edited the study along with peers from the U.S. data center.

The study focused on La Nina conditions, Stott noted, but future research will look at non-La Nina years as well.

La Nina, which cools Pacific waters, alternates with El Nino, which warms Pacific waters. Both can impact weather worldwide and in La Nina's case it typically warms up the southern U.S. 

As the science behind the framework improves, Stott said, "we'll be able to address more difficult questions" about the relationship between severe weather and climate change. 

The 2011 Texas drought revealed the remains of a town long covered by Lake Buchanan. KCEN's Joshua Skurnik reports.

The Texas component of the study compared rainfall and temperature data from La Nina years in the 1960s (1964, 1967, 1968) to present day (2011 data was not yet available so the scientists used 2008, another strong La Nina year.)

The amount of computer processing time needed was enormous, so the scientists reached out to an existing network of "citizen scientists" who allow their networked computers to be used at off-hours, Tom Peterson of the U.S. climate data center told msnbc.com.

The study reached conclusions about other extreme events last year as well, but only provided odds for the cold/warm extremes seen in Britain.

U.S.: First half of 2012 warmest on record

December 2010 was extremely cold in Britain, but the odds of that happening have been halved due to climate change, the study concluded. November 2011 was extremely warm, an event that's now 60 times more likely than in the 1960s, the data show.

Several other extreme weather events were studied using different methodologies, which did not calculate the odds that warming had an impact.

Still, a climate role was ruled out in Thailand's worst flooding in 70 years. That flooding was not accompanied by higher than normal rainfall, the experts noted. They instead cited flood-control decisions on the ground as key factors.

Two other events -- East Africa's drought and Western Europe's heat wave -- appear to have been influenced by warming in addition to La Nina, the study stated, but the extent was not quantified.

The study, the first of what is expected to be an annual look back at extremes and climate, was published in the July issue of the Bulletin of the American Meteorological Society.

It was announced in conjunction with the 22nd annual global State of the Climate report released by the U.S. and the American Meteorological Society.

The 43 indicators tracked in 2011 -- ranging from thinning Arctic sea ice to more acidic oceans -- continued to show a warming trend, according to the State of the Climate report.

"Those indicators," said Thomas Karl, head of the National Climatic Data Center, "show what we expect to see in a warmer world."

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