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North Carolina's coast is 'hot spot' for rising sea levels

Some researchers say forecast of 39-inch rise by 2100 is too low

State legislators last summer ignored research that shows sea-level rise will accelerate its creep up North Carolina’s coastline this century.

This week, waves of science will say they were wrong.

Sea level was a hot topic – and North Carolina lawmakers a butt of jokes – as the Geological Society of America began its annual meeting in Charlotte on Sunday, days after Hurricane Sandy swamped New York and New Jersey.

Some researchers said the 39-inch rise a state science panel expects by year 2100 may be far too low. Other new studies say North Carolina is part of an Atlantic coast “hot spot” where seas are rising far faster than in the rest of the world.

The scientists also say there’s a lot they can’t predict.

“We’re going to have a meter of sea-level rise. I can’t tell you if it will be 50 years or 100 years from now,” said panel member Rob Young, who leads the Program for the Study of Developed Shorelines at Western Carolina University.

“We’re going to get to that meter whether it’s on a straight line into the future or in that dramatic uptick that the vast majority of scientists believe is happening.”

Atlantic coast sea level rise

Sea level along 600 miles of the Atlantic coast from Cape Hatteras to north of Boston has risen three to four times faster since 1990 than it has globally, says a U.S. Geological Survey study published in June. That alone is enough to add 8 to 11 inches to the global average this century.

“It turns out it’s the only area of acceleration presently going on along the coast of the United States,” said oceanographer Asbury Sallenger, who lead the project. The rate of rise farther south, in places like Charleston and Savannah, shows no such trend, he said.

Sea level varies widely depending on where it is measured, due to differences in land characteristics and ocean currents, water temperatures and salinity.

Sallenger traces the likely cause of the hot spot to a region of frigid Atlantic water south of Greenland that is warming, altering the flow of currents and the tilt of the sea surface.

Other studies support those findings. Sea level on the Atlantic coast has risen since the late 19th century at the fastest pace in 2,000 years, the University of Pennsylvania’s Benjamin Horton, Yale scientist Andrew Kemp and colleagues showed. East Carolina University geologist Stanley Riggs’ team found a similar trend in northeastern North Carolina.

The Intergovernmental Panel on Climate Change, in its latest report, predicted in 2007 that global sea level would rise no more than about 20 inches this century. But that didn’t include the unpredictable impact of massive, fast-melting ice sheets in Greenland and Antarctica.

Melting ice is “absolutely the key factor,” said Richard Peltier, director of the University of Toronto’s Centre for Global Change Science.

“I think we would all agree, even the most conservative IPCC persons, that the IPCC number is very conservative,” Peltier said, with some projections of about 59 inches. “It’s got nowhere to go but up, but by how much is a bit of a mug’s game.”

Legislators decide to delay

The science panel’s recommendation that North Carolina plan for much higher seas by year 2100 prompted a tsunami-size backlash in coastal counties.

An economic development group insisted the science was flawed, and said it would halt development on wide swaths of land already barely above sea level.

N.C. legislators first proposed a law that would allow calculations of future sea-level rise to be based only on past trends, not on scientific evidence of accelerated rise.

The final version, ratified in August, delays estimating future rates until 2016. It instructs the science panel to reassess whether sea level could fall or the rate of rise slow as well as speed up. It orders the state Coastal Resources Commission to consider “historical calculations” along with computer models of the future.

The 22,000-member geological society’s position is that human activities account for most of the global warming since the mid-1990s. On Sunday it honored author and climate activist Bill McKibben with its President’s Medal.

The rate of global sea level rise has increased since the early 1990s to about 3 millimeters a year, sharply higher than the 20th-century average of 1.7mm.

“What that tells you is that nothing is going to get better in the coast in the future, even without a (further) acceleration,” said Young, the Western Carolina University geologist.

Some scientists aren’t sure that trend will last.

Satellite data shows that the rate of acceleration is slowing, says University of Florida researcher Robert Dean. Studies show historic up-and-down cycles that fit such patterns.

“The question is whether the satellites are showing an oscillation or a new trend,” he said.

‘Sets the stage for a little Nor’easter’

Hurricane Sandy stayed well off the North Carolilna coast but still overwashed N.C. 12, which runs through the Outer Banks, in three places. Winter storms could turn those sites into new inlets, said Stan Riggs of East Carolina University.

Sandy “sets the stage for a little Nor’easter to just pummel the hell out of the Outer Banks this winter,” Riggs said. New openings in the islands could quickly expose the protected sounds behind them to much higher tides, threatening the communities on their shores.

Rising seas will only make storm surges higher, scientists say.

“The most obvious aspect of climate change to Hurricane Sandy is not necessarily that storms have gotten bigger or more intense,” said Sallenger, the Geological Survey scientist. “It’s that the seas are definitely rising – we can see it and measure it.”

Henderson: 704-358-5051; Twitter: @bhender
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