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Will we ever understand 2012 drought? Study blames 'random weather' (+video)

The drought of 2012 was more about unusual weather patterns than global warming, says a study. But its authors acknowledge the record-smashing event likely will be a puzzle for years to come.

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Soil moisture across the six states "was not severely stressed," says Richard Seager, a climate scientist at Columbia University's Lamont-Doherty Earth Observatory in Palisades, N.Y., and a member of the team that performed the analysis.

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But as May arrived, things changed. Three distinct shifts in circulation patterns between May and August collectively conspired to keep the Central Plains virtually rain-free. During the spring and early summer, storm systems that move through the Plains and typically draw their moisture from the Gulf of Mexico were diverted north into Canada. These patterns also prevented the formation of summer-evening thunderstorms that bring needed rain later in the season.

The researchers also noticed that a pattern in sea-surface temperatures in the Pacific and Atlantic that had been present during the Dust Bowl droughts of the mid 1930s reappeared in 1999 and has persisted ever since – through the hottest decade globally on record.

This change in sea-surface temperatures could suggest a long-term predisposition for severe drought in the Central Plains, the team suggests.

The report and submitted paper will hardly be the last word on what was a historic drought or on the potential contribution it received from global warming, Mr. Hoerling adds.

Indeed, other researchers note that the study has an element of "what's new?" to it.

"The report certainly did not ask the right questions if it was interested in the role of global warming or human influences," writes Kevin Trenberth, a climate researcher at the National Center for Atmospheric Research in Boulder, Colo., in an e-mail. "We know that natural variability plays a major role, and the question then is what did the global warming aspects do, and why did we break so many records?"

He notes that among the hallmarks that models have identified in droughts influenced by global warming are faster starts and more intense conditions. These contribute to the withering vegetation and wildfires that further reinforce the warming that accompanies drought.

"This is why we broke so many records," he says of the summer's temperatures.

As for drought-forecasting improvements, Dr. Trenberth notes that among other avenues researchers are pursuing, they are trying to upgrade forecasting models, which currently do a better job handling factors that influence drought in the winter than they do handling those same influential factors in the summer.

The report "is not definitive," Hoerling acknowledged during one of Thursday's briefings. "We will spend years on this question. So come back in 80 years and you'll hear me again – I'll look a little bit different – talking about the 2012 drought, I'm sure."


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