Study: Global Warming Doubles Risk of "Katrina-Magnitude" Events

Warming global temperatures have doubled the risk of "Katrina magnitude events," says a new study published Monday in the journal Proceedings of the National Academy of Sciences.

By analyzing the dramatic and sudden increase in water levels--or storm surges--which occur as a result of fierce hurricane winds and low central air pressure, researchers have found that even a 'statistically downcast' estimate of a 1.8degF increase in global average surface temperatures would result in a two-fold to seven-fold increase in the risk of these devastating events.

The latest climate projections, however, are far more dramatic with estimates falling between 3.2degF and 7.2degF for global temperature increase by 2100.

"Our study shows that extreme (storm) surges become more frequent in a warmer climate, and that the relative change in frequency is much more pronounced for the most extreme events," said lead author Aslak Grinsted, a climate researcher at the University of Copenhagen.

"Storm surges," writes Climate Central's Andrew Freedman, "are hurricanes' greatest killer, a point that was driven home again just last year, when Hurricane Sandy killed at least 72, mainly along the coast of New Jersey and New York."

Similarly, when Hurricane Katrina hit the gulf coast, water levels along some parts of the shoreline rose as high as 28 feet above the astronomical tide level, leveling entire communities and contributing to the death of more than 2,000 people.

"I think our study is important," said Grinstead, "because it says that coastal adaptation measures should include changes in surge statistics in addition to local sea level rise."

Reasoning that tidal gauge records could be used to reveal the biggest storm surges, scientists from the University of Copenhagen, Beijing Normal University and NERC's National Oceanography Center (UK) analyzed data dating back to 1923 from six tidal gauges in the southeastern US coast--from Galveston, Texas to Atlantic City, New Jersey.

Factoring out other influences, such as sea level rise, the researchers determined that "the warming that took place during the 20th century has already led to a doubling of the risk of Katrina-magnitude storm surge events," Climate Central reports. Adding, "a warming of just 0.72degF could cut in half the return period of Katrina-magnitude surges, thereby making them a far more frequent occurrence."

Previous studies have suggested a link between warming temperatures and an increased risk of hurricanes but scientists have been reluctant to assume causality because they have been unable to isolate the trend from other competing factors - such as El Nino, tropical temperatures or droughts in the Sahel region of Africa.

"Scientists have been extremely careful about saying some event has a cause. But here, it's fair to say that warmer conditions make hurricanes more probable," Grinsted concluded.

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