A 0.4 C warming corresponded to doubling of the frequency of extreme storm surges, the study found. "With the global warming we have had during the 20th century, we have already crossed the threshold where more than half of all 'Katrinas' are due to global warming," Grinsted said.
James Elsner, a climate scientist at the University of Florida, said he agrees with the study's main finding, but thinks the modeling underestimates the effects of climate factors such as the El Niño/ La Niña Southern Oscillation (ENSO) index, and the North Atlantic Oscillation (NAO). Studies have shown that the warm El Niño events mean fewer hurricanes in the Atlantic, while the NAO influences storm tracks across the ocean basin.
"As the planet warms up and the oceans get warmer, the chances of stronger storms goes up," Elsner said. "I think it's an interesting exercise, but I think statistically, it's got some issues," he told OurAmazingPlanet.
Storm surges and sea level rise
Grinsted is concerned about the combined effects of future storm surge flooding and sea level rise, which adds to the base of the storm surge.
"I think what will be even more important is the background sea level rise, and that is something that is very hard to model," he said.
Hurricane Sandy brought an 11.9-foot (3.6 meters) surge to southern Manhattan, plus a boost from the high tide, creating a storm tide as high as 13.88 feet (4.2 m).
Hurricane Katrina caused storm surge flooding of 25 to 28 feet (7.6 to 8.5 m) above normal tide level along portions of the Mississippi coast and 10 to 20 feet (3 to 6.1 m) above normal tide levels along the southeastern Louisiana coast.
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