Rising seas 'to hit New York hard'

A predicted slowdown in Atlantic Ocean currents will cause sea levels along the US northeast coast to rise twice as fast as the global average, exposing New York and other big cities to violent and frequent storm surges, according to a new study.

Manhattan's Wall Street, barely a metre above sea level, for example, will find itself underwater more often as the 21st century unfolds, said the study, published online on Sunday in Nature Geoscience.

Sea levels vary across regions by up to 24cm, influenced in part by powerful currents that course around the globe in a pattern called the thermohaline circulation.

In the Atlantic, warm water moving north along the surface from the Gulf of Mexico helps temper cold winters in western Europe and along the US east coast, while frigid Arctic waters run south along the bottom of the sea.

The UN's Intergovernmental Panel on Climate Change (IPCC) concluded in early 2007 that expanding ocean water driven by climate change will drive up sea levels, on average, anywhere from 18 to 59cm by 2100, depending on how successful we are at slashing greenhouse gas emissions.

This rising water mark will erase several island nations from the map, and is likely to cause devastation in Asian and African deltas home to tens of millions of people.

More recent studies, taking the impact of melting ice sheets in Greenland and the Western Antarctic into account, forecast an even higher increase of at least 1 metre over the same period.

Jianjun Yin of Florida State University and two colleagues wanted to find out what impact these sea level rises would have at a regional level, especially along the American eastern seaboard.

The researchers analysed the projections of nearly a dozen state-of-the art climate change models, under three different greenhouse gas scenarios.

They found that sea levels in the North Atlantic adjusted in all cases to the projected slowing of the Gulf Stream and its northward extension, the North Atlantic Current.

The weakened currents account for nearly half of a predicted sea rise - from thermal expansion alone - of 36 to 51 cm for the US northeastern coast, especially near New York, they found.

"This will lead to the rapid sea level rise on the Northeast coast of the United States," Yin told AFP by phone.

And if, under the influence of melting ice sheets, "the global sea level rise is higher, the relative sea level rise will be superimposed. Proportionally it would be the same," he said.

Rapid sea level increases would put cities such as New York, Boston, Baltimore and Washington, DC at significantly greater risk of coastal hazards such as hurricanes and intense winter storm surges.

A study released last year by the Cambridge, Massachusetts-based Union of Concerned Scientists showed that, due to rising sea levels, once-in-a-century storms would occur on average every 10 years by 2100.

A large belt around the tip of Manhattan - included Wall Street - would have a 10 per cent chance of flooding in any given year, it concluded.

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