By ecoRI News staff
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| Misquamicut after the Hurricane of 1938 |
The findings could have implications for the intensity and
frequency of hurricanes the United States could experience as ocean
temperatures increase as a result of climate change, say study’s authors.
A new record of sediment deposits from Cape Cod show evidence that
23 severe hurricanes hit New England between the years 250 and 1150, the
equivalent of a severe storm about once every 40 years.
Many of these
hurricanes 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 (Hurricane Katrina) or category 4 storms (Hurricane Hugo)
that would be catastrophic if they hit the region today, according to Jeff
Donnelly, a WHOI scientist and the study’s lead author.
The study is the first to find evidence of historically unprecedented hurricane activity along the northern East Coast, Donnelly said. It also extends the hurricane record for the region by hundreds of years, back to the first century, he said.
“These records suggest that the pre-historical interval was unlike
what we’ve seen in the last few hundred years,” Donnelly said.
The most powerful storm to 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.
The intense prehistoric hurricanes documented by the study were
fueled in part by warmer sea surface temperatures in the Atlantic Ocean during
the ancient period investigated in the study than have been the norm off the
East Coast during the past few hundred years.
However, as oceans temperatures
have slowly inched upward 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, Donnelly said.
He said the new study could help scientists better predict the
frequency and intensity of hurricanes that could hit the U.S. coast in the
future.
“We hope this study broadens our sense of what is possible and
what we should expect in a warmer climate,” Donnelly said. “We may need to
begin planning for a category 3 hurricane landfall every decade or so rather than
every 100 or 200 years. The risk may be much greater than we anticipated.”
Donnelly and his colleagues examined sediment deposits from Salt
Pond in Falmouth. The pond is separated from the ocean by a 4.3- to
5.9-foot-high 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 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. The study suggests that many powerful storms
spawned in the tropical Atlantic between 250 and 1150 also battered the East
Coast.
The deposits revealed that these early storms were more frequent,
and in some cases were likely more intense, than the most severe hurricanes
Cape Cod has seen in historical times, including Hurricane Bob and a 1635
hurricane that generated a 20-foot storm surge, according to Donnelly.
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 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 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
study. Previous research has also shown that warmer ocean surface
temperatures fuel more powerful storms.