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East Coast faces faster sea level rise

Cities from North Carolina to Massachusetts see waters rising more rapidly

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4:14pm, June 24, 2012
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Property values aren’t all that’s been rising in Manhattan. The height of the water lapping up against the Big Apple and many East Coast cities has been creeping up faster in recent decades.

“We have direct evidence of a hot spot stretching from Cape Hatteras in North Carolina to just above Boston,” says Asbury Sallenger Jr., an oceanographer at the U.S. Geological Survey’s St. Petersburg Coastal and Marine Science Center in Florida. “The area has an unusual sea level rise acceleration compared to the rest of the United States.”

Global warming could be driving the acceleration, researchers report online June 24 in Nature Climate Change. With temperatures still climbing, further ocean rises could increase the risk of flooding, encroach on wetlands and give hurricane storm surges extra punch.

Climate change has, on average, raised the surface of the world’s oceans in recent decades by melting glaciers and causing seawater to expand as it warms. But the rise hasn’t been uniform, like water filling a bathtub. It has happened at different speeds in different places, thanks to wind patterns, currents and other regional factors that shape ocean surfaces.

Sallenger and colleagues studied the situation on the East Coast using 60 years of data collected by sensors floating in the Atlantic Ocean. From 1980 to 2009, sea levels along about 1,000 kilometers of coast rose faster than from 1950 to 1979 — a gain in speed of about 2 millimeters per year, or about three to four times the average global acceleration.

If this acceleration continues at its current rate, New York City would be on track for up to 29 centimeters of sea level rise by 2100. That’s in line with previous predictions from a simulation based on probable climate change scenarios.

Long-term climate trends may have created this hot spot by changing ocean currents, says Sallenger. With the atmosphere heating, parts of the North Atlantic have warmed and freshened. Computer simulations suggest the decreasing density of these waters could weaken the powerful Gulf Stream and North Atlantic Current, which keep water away from the East Coast.

But don’t sell your beachfront property quite yet. This theory lacks the support of actual measurements that show a waning of ocean circulation. Some scientists credit the sea level speedup to weather patterns that could soon reverse.

The recent trend may reflect fluctuations in pressure or temperature that oscillate over decades, says James Houston, director emeritus of the U.S. Army Corps of Engineers’ Engineer Research and Development Center in Vicksburg, Miss. Sea levels along the East Coast fell before 1960, he says, and may very well do so again.

“If the paper would have been written in 1960 … it would probably have concluded that there was a cold spot,” says Houston. “We may be back to a cold spot from 2010 to 2039.”

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