Katrina-sized hurricanes regularly hit North America's east coast centuries ago and could return to plague the U.S. eastern seaboard again because of climate change, researchers say.
Sediment deposits collected from Cape Cod have yielded evidence of exceptional hurricane activity along the northeast coast from about 800 to 1700 years ago, they say.
That period saw warm ocean temperatures similar to what is expected in the coming centuries with global warming and climate change, geoscientists at the Woods Hole Oceanographic Institute and the University of Massachusetts Amherst explain.
Hurricanes stronger than any recorded in modern times were fairly frequent during that past period, occurring around every 40 years, the researchers report in Earth's Future, an American Geophysical Union journal.
"These records suggest that the pre-historical interval was unlike what we've seen in the last few hundred years," says Wood Hole scientist Jeff Donnelly, lead author of the study.
Between the years A.D. 250 and 1150, some 23 large hurricanes left their traces in the sediments the researchers analyzed.
They looked at Salt Pond near Falmouth on Cape Cod, which is separated from the ocean by a tall sand barrier. Strong hurricanes have pushed sediments over that barrier and into the pond where they have remained undisturbed for centuries, leaving a signature of those storms in sediment cores extracted from as deep as 30 feet down in the pond's bottom.
Previous studies have found evidence of similarly elevated hurricane activity in the same period in more southerly areas of the western North Atlantic Ocean basin from the Caribbean to the Gulf Coast.
Most of the hurricanes back then were probably Category 3 storms, like 2005's Hurricane Katrina, or Category 4 events like Hurricane Hugo in 1989, the researchers estimate.
Any such hurricane hitting the U.S. East Coast today would be catastrophic, Donnelly says.
Ocean temperatures off New England, which have been slowly rising for the last several decades, are today higher than prehistoric levels, the researchers say.
The rise is likely to continue during this century with warming climate, a situation that could elevate the risk of devastating storms, they say.
"We hope this study broadens our sense of what is possible and what we should expect in a warmer climate," Donelly says.
"We may need to begin planning for a Category 3 hurricane landfall every decade or so rather than every 100 or 200 years," he warns. "The risk may be much greater than we anticipated."
