Ocean levels are rising three-to-four times faster than the worldwide average along a 620-mile stretch from central North Carolina to north of Boston, according to a new study published in the journal Nature Climate Change.

Sea level rise is already proving to be a serious concern for New York City's infrastructure, such as the South Ferry station.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, the study concluded.

"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.

One possible explaination for 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.

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.