Sea levels along a quarter of the East Coast, including around New York City, are rising more quickly than the global average, according to a new study.
The study, published last week in the journal Nature Climate Change finds that sea levels are rising three to four times more quickly than average along a 620-mile stretch from central North Carolina to north of Boston.
"There's been a strong suggestion of such a hotspot occurring from climate models that have been published over the last several years," said U.S. Geological Survey oceanographer Asbury Sallenger, who led the study. "And our approach was to use real data — tide-gauge data from around the United States — to test whether we could see a signal that this is representative of what the climate models project. And, I think we do see a very similar signal to that."
Since about 1990, sea-level rise along this portion of the Atlantic coast has increased 2 to 3.7 millimeters per year, while the global increase over the same period was 0.6 to 1.0 millimeter per year, according to the study.
One theory to explain the accelerated rise involves the gradual warming of the area south of Greenland, which slows down the ocean currents that run south to north along the eastern seaboard, Sallenger said.
Scientists believe the slower currents change the slope of the seas, pushing up sea levels along that portion of the East Coast. More work needs to be done to test that theory.
"We should not expect over the 21st Century for sea-level rise to be a uniformly rising process like filling a bathtub," Sallenger said. "There will be significant variation around the world and there will be a whole variety of reasons why this is playing out."
Sallenger says the additional 20 to 30 percent rise in sea level in the hotspot area will be especially noticed during extreme storms such as last year's Hurricane Irene last year, when storm surge and flooding will be that much worse. That storm prompted New York City officials to order evacuations of low-lying areas, as a precaution.
"As sea levels rise over the next century or during the present century, a storm that may have occurred decades ago of a certain strength," Sallenger said, "if that same-storm occurs decades ahead from now, it's coming in riding on this sea level rise and it's enough that that storm surge will be that much higher, the reach of the waves will be that much higher onto the beach or into a building or over a sea wall."