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Big jump seen in hurricane-related storm surges

Mark Lennihan / AP

In this file photo, Louise McCarthy carts belongings from her flood-damaged home as she passes the charred ruins of other homes in the Breezy Point section of the Queens borough of New York, Nov. 14. A fire destroyed more than 100 homes in the oceanfront community during Superstorm Sandy.

Massive hurricanes that push piles of seawater city-blocks inland when they howl ashore will increase dramatically as the planet continues to warm, according to a new study.

"It is pretty clear" that climate change must affect hurricane activity "somehow," Aslak Grinsted, a climate scientist at the University of Copenhagen, told NBC News. "But it is not clear exactly how."

The study charts a novel path toward an answer. Grinsted and his colleagues combined different types of models used to study the question, validating and weighting their importance based on how well they explained past storm surges seen at six tide gauges along the Atlantic and Gulf coasts.

For every degree Celsius (1.8 degree Fahrenheit) of warming, the scientists find a twofold to sevenfold increase in the type of storm surge seen when Hurricane Katrina struck in 2005. 

In a paper published Monday in the Proceedings of the National Academy of Sciences, the researchers write their finding "demonstrates a greatly increased Atlantic hurricane surge threat in a warmer world," which will be "further exacerbated by rising sea level."

Competing methods
Over the years, scientists have looked for answers through analysis of satellite observations, ship logs, and other historical documents, which are limited by quality, spatial coverage and time and give varying answers. 

Aslak Grinsted / Niels Bohr Institute

Extreme storm surges like that caused by Hurricane Katrina (2005) become more frequent in globally warming climate new research shows.

Others studies have used climate models focused on sea surface temperature in the main region of the Atlantic Ocean where hurricanes form. These suggest warming seas provide more fuel for hurricanes and produce a corresponding uptick in storm frequency or intensity or both, Grinsted said.

Different models, however, focus on the difference in temperature between the region where hurricanes form and tropical ocean temperatures. These models show little increase in hurricane activity since that temperature difference may not change much as the planet warms.

Grinsted and colleagues combined the two model approaches. "The end result is something that is very consistent with the regional sea surface temperature model," Grinsted said. 

The model also picks up a known decrease in hurricane activity during El Nino years, which is related to warmer-than-average sea surface temperatures in the eastern Pacific Ocean and increased wind shear.

Misleading result?
The paper is unlikely to settle the scientific debate over the relationship between hurricane activity and warming. 

Judith Curry, an atmospheric scientist at the Georgia Institute of Technology who is actively researching the relationship, told NBC News in an email that the new paper is "very misleading."

For one, she said their tide gauge dataset is inferior to the standard dataset of landfalling hurricanes maintained by the National Hurricane Center, which makes using the tide gauge to make statistical projections of future storm surges "unconvincing."

Greg Holland, a scientist with the National Center for Atmospheric Research in Boulder, Colo., said he liked the tide gauge approach. 

"Creative and independent approaches like this provide new information for helping assess hurricane climatologies," he said in an email to NBC News, but added that surge information can only tell so much about a particular storm.

"As Hurricanes Kerry and Ike have clearly shown, major surges can occur from not particularly intense hurricanes," he noted.

John Roach is a contributing writer for NBC News. To learn more about him, check out his website

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