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Monster Hurricanes Once Plagued East Coast and May Return

While Europe was going through the Middle Ages, America's East Coast was being pummeled by hurricanes at least as intense as Katrina every 40 years or so, climate detectives say.

Between the years 250 and 1150, almost two dozen Category 3 and Category 4 storms left their signatures in sediment deposits in Salt Pond on Cape Cod, Massachusetts, the researchers report in a study published online Wednesday by Earth's Future, one of the American Geophysical Union's open-access journals. Hurricane Katrina was a Category 3 storm in 2005, while 1999's Hurricane Floyd is an example of a Category 4.

Such storms would be catastrophic if they hit the northeast U.S. today, according to lead author Jeff Donnelly of the Woods Hole Oceanographic Institution. "These records suggest that the pre-historical interval was unlike what we've seen in the last few hundred years," Donnelly said in a news release.

Donnelly and his colleagues suggest that shifts in sea surface temperatures in the western North Atlantic contributed to the frequency of intense storms — and that warming seas could bring a return to those conditions.

"We may need to begin planning for a Category 3 hurricane landfall every decade or so rather than every 100 or 200 years," he said. "The risk may be much greater than we anticipated."

What’s causing our weather extremes? 1:01

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— Alan Boyle

In addition to Donnelly, the authors of "Climate Forcing of Unprecedented Intense-Hurricane Activity in the Last 2,000 Years" include Andrea Hawkes, Philip Lane (deceased), Dana MacDonald, Bryan Shuman, Michael Toomey, Peter van Hengstum and Jonathan Woodruff.