Rising sea levels: Is global warming making the US East Coast a 'hot spot?'

The pace of sea-level rise along much of the East Coast is accelerating three to four times faster than the worldwide average, a US Geological Survey study says. Global warming is the chief suspect.

By Pete Spotts,?Staff writer / June 25, 2012

This Aug. 2011 photo shows a flooded road on Hatteras Island, N.C., after Hurricane Irene swept through the area the previous day cutting the roadway in five locations. From Cape Hatteras, N.C., to just north of Boston, sea levels are rising much faster than they are around the globe.

Jim R. Bounds/AP

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The pace of sea-level rise along a swath of the US East Coast ? from north of Boston down to North Carolina's Cape Hatteras ? is accelerating three to four times faster than the worldwide average, according to a new study from the US Geological Survey (USGS), turning the region into a hot spot for sea-level rise.

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At stake: the increased vulnerability of coastal communities to severe damage from storm surges or even high surf caused by storms off shore.

The prime suspect: global warming, through its direct effect on heating water at the ocean surface as well as the effect warmed seawater and air temperatures can have on speeding the pace at which Greenland is losing ice.

Warmer seawater in the North Atlantic and increasing amounts of fresh water from?melting Greenland ice can slow ocean-circulation patterns in the ocean basin, which can trigger the accelerated rise, modeling studies have suggested.

Indeed, models indicated that the East Coast could develop such a sea-level hot spot ? and in the location the new study identifies ? because of these factors, explains Asbury Sallenger Jr., a research oceanographer who heads a USGS project to assess changes in the hazards that US coastal communities could face from climate change.

But earlier real-world measurements did not always support the theoretical models. One study, published in May 2011, looked at more than a century's worth of tide-gauge measurements from around the US and globally. The team not only found no US hot spot. It found no acceleration of sea-level rise over the 20th century and into the first decade of the 21st.

The results triggered spirited debates as to why, in the face of other evidence to the contrary, the team came up dry. If the warming the climate has experienced during the past century has triggered no rise in sea-levels, projections of future increases ? already laced with uncertainties ? would be heavily overstated at best.

Dr. Sallenger and two USGS colleagues decided to take their own look.

They used tide-gauge measurements from around the US coastlines spanning a 60-year period beginning in 1950. They found that from 1950 through 2009, as global average sea levels rose at a pace of 0.59 millimeters a year, they rose 1.97 mm per year in the East Coast ?hot spot.? Between 1970 and 2009, the pace picked up, with global average sea levels rising 0.98 mm per year and the hot spot's pace increasing to 3.8 mm per year.

South of Cape Hatteras the pace shows no significant change for either time span. North of Boston, the pace either was zero or slightly negative for the 1950-2009 period, but between 1970-2009, the rate rose into positive territory well into the Canada, Sallenger's team reports.

The results were "surprising, actually," Sallenger says. "We found what we call a hot spot of acceleration. This is the only location within the country and a good chunk of North America where this kind of thing is happening."

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