Climate: Warming oceans may increase New England hurricane risk

Hurricanes and global warming
A NOAA satellite image of Hurricane Bob, which raked the New England coast in 1991.

Historic record shows series of intense storms during eras of warmer sea surface temps

Staff Report

FRISCO — Climate researchers say New England’s coastal communities may need to prepare for major hurricane strikes sooner rather than later as the Atlantic Ocean continues to warm.

“We may need to begin planning for a category 3 hurricane landfall every decade or so rather than every 100 or 200 years,” said Jeff Donnelly, a scientist at Woods Hole Oceanographic Institution in Massachusetts, explaining that new research findings show that a string of giant storms pummeled the region during the first millennium, from the peak of the Roman Empire into the height of the Middle Ages.

The study examined a new record of sediment deposits at Cape Cod, which suggests that as many as 23 severe hurricanes hit New England between 250 and 1150. Many of these storms were likely more intense than any that have hit the area in recorded history, according to the study.

The prehistoric hurricanes were likely category 3 storms like Hurricane Katrina, or category 4 storms like Hurricane Hugo, which would have catastrophic impacts on the region today, according to Donelly, lead author of the new paper accepted for publication in Earth’s Future, a journal of the American Geophysical Union.

“These records suggest that the pre-historical interval was unlike what we’ve seen in the last few hundred years,” said Donnelly.

The most powerful storm to ever hit Cape Cod in recent history was Hurricane Bob in 1991, a category 2 storm that was one of the costliest in New England history. Storms of that intensity have only reached the region three times since the 1600s, according to Donnelly.

Warm oceans

The powerful hurricanes during that earlier era were partly fueled by warmer sea surface temperatures in the Atlantic. In recent decades, the tropical North Atlantic sea surface has surpassed the warmth of prehistoric levels and is expected to warm further over the next century as the climate heats up, potentially setting the stage for the formation of powerful hurricanes.

“The risk may be much greater than we anticipated,” Donelly added, explaining in a press release how the researchers found layers of storm-driven sediment in Salt Pond, near Falmouth on Cape Cod. The pond is separated from the ocean sand barrier. Over hundreds of years, strong hurricanes have deposited sediment over the barrier and into the pond where it has remained undisturbed.

The researchers extracted nine-meter (30-foot) deep sediment cores that they then analyzed in a laboratory. Similar to reading a tree ring to tell the age of a tree and the climate conditions that existed in a given year, scientists can read the sediment cores to tell when intense hurricanes occurred.

The study’s authors found evidence of 32 prehistoric hurricanes, along with the remains of three documented storms that occurred in 1991, 1675 and 1635.

The prehistoric sediments showed that there were two periods of elevated intense hurricane activity on Cape Cod – from 150 to 1150 and 1400 to 1675. The earlier period of powerful hurricane activity matched previous studies that found evidence of high hurricane activity during the same period in more southerly areas of the western North Atlantic Ocean basin – from the Caribbean to the Gulf Coast.

High hurricane activity continued in the Caribbean and Gulf of Mexico until 1400, although there was a lull in hurricane activity during this time in New England, according to the new study.  A shift in hurricane activity in the North Atlantic occurred around 1400 when activity picked up from the Bahamas to New England until about 1675.

The new study suggests that many powerful storms spawned in the tropical Atlantic Ocean between 250 and 1150 also battered the U.S. East Coast.

The periods of intense hurricanes uncovered by the new research were driven in part by intervals of warm sea surface temperatures that previous research has shown occurred during these time periods, according to the new study. Previous research has also shown that warmer ocean surface temperatures fuel more powerful storms.

The sediment coring and analysis by Donnelly and his colleagues “is really nice work because it gives us a much longer period perspective on hurricanes,” said Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology in Cambridge. “It gives you something that you otherwise wouldn’t have any knowledge of.”

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