New York Seas to Rise Twice as Much as Rest of U.S.

Richard A. Lovett, National Geographic News 15 Mar 09;

Sea levels around New York City and much of the U.S. Northeast will rise twice as much as in other parts of the United States this century, according to new climate models.

Driven by changes in ocean circulation, the rapid sea level rise will bring increased risk of damage from hurricanes and winter storm surges, researchers say.

"Some parts of lower Manhattan are only 1.5 meters [5 feet] above sea level," said lead study author Jianjun Yin, a climate modeler at Florida State University.

"Twenty centimeters [8 inches] of extra rise would pose a threat to this region."

Yet New York, Boston, and Washington, D.C., area seas will rise 14 to 20 inches (36 to 51 centimeters) by 2100, according to the study, published online today in the journal Nature Geoscience.

Other U.S. cities, such as Miami and San Francisco, are expected to see only half as big an increase in sea levels.

Gulf Stream Forces to Weaken?

The reason U.S. Northeast seas are expected to rise disproportionately is because the forces that generate the North Atlantic's Gulf Stream ocean current are projected to weaken in the coming decades.

New climate models predict that global warming will reduce the sinking of cold water that drives the Gulf Stream. As a result, the deep ocean will begin to warm in the North Atlantic, Yin aid.

As water around the current warms, it will expand, adding to the sea level rise caused by global factors such as melting ice caps and icebergs, the study says.

Ice Free Arctic by 2100?

Adding to those global factors may is an Arctic Ocean that appears to be melting rapidly, according to Julien Boé, a postdoctoral researcher at the University of California, Los Angeles, in another climate study in today's Nature Geoscience.

After comparing a range of models with actual observations, his team predicts that the Arctic Ocean will be ice free during September as early as the end of this century.

Such studies are vital, experts say, because they offer scientists a more precise idea of how different regions might prepare for potential damage due to global warming.

"In both papers," Boé said in an email, "the objective is to improve the projections of important aspects of regional climate change."

Warming to make N.Y. vulnerable to storms: study
Reuters 15 Mar 09;

NEW YORK (Reuters) - Global warming should lift sea levels along the U.S. Northeast nearly twice as fast as global rates this century, putting New York City at risk to damage from hurricanes and winter storm surges, scientists said.

"The northeast coast of the United States is among the most vulnerable regions to future changes in sea level and ocean circulation, especially when considering its population density," said Jianjun Yin, a climate modeler at Florida State University.

Yin, who published a study on rising seas in the journal Nature Geoscience on Sunday, said sea levels along the Northeast should rise 8.3 inches more than the global mean level sea rise by 2100. Well before then, New York City will be at risk of severe flooding from storm surges because many parts of the city are only slightly above sea level.

The rising seas could also submerge low-lying land in and around the city, erode beaches, and hurt estuaries, some of the most diversely populated ecosystems.

Climate scientists say higher temperatures caused by heat-trapping emissions from tailpipes, smokestacks and the burning of forests have the potential to raise sea levels by melting land ice, such as the Greenland icesheet, and expanding water in the ocean.

The U.S. Northeast's coast is particularly vulnerable as global warming slows the Atlantic meridional overturning circulation, which is basically a natural conveyor belt that carries warm upper waters to northern latitudes and returns colder waters southward.

Yin and colleagues from the University of Illinois at Urbana-Champaign and the Geophysical Fluid Dynamics Laboratory at Princeton University studied 10 climate models used by the U.N.'s Intergovernmental Panel on Climate Change in their study. Yin was funded by the U.S. Department of Energy's science department.

(Reporting by Timothy Gardner; Editing by Christian Wiessner)

Northeast US to suffer most from future sea rise
Seth Borenstein, Associated Press Yahoo News 15 Mar 09;

WASHINGTON – The northeastern U.S. coast is likely to see the world's biggest sea level rise from man-made global warming, a new study predicts.

However much the oceans rise by the end of the century, add an extra 8 inches or so for New York, Boston and other spots along the coast from the mid-Atlantic to New England. That's because of predicted changes in ocean currents, according to a study based on computer models published online Sunday in the journal Nature Geoscience.

An extra 8 inches — on top of a possible 2 or 3 feet of sea rise globally by 2100 — is a big deal, especially when nor'easters and hurricanes hit, experts said.

"It's not just waterfront homes and wetlands that are at stake here," said Donald Boesch, president of the University of Maryland Center for Environmental Science, who wasn't part of the study. "Those kind of rises in sea level when placed on top of the storm surges we see today, put in jeopardy lots of infrastructure, including the New York subway system."

For years, scientists have talked about rising sea levels due to global warming — both from warm water expanding and the melt of ice sheets in Greenland and West Antarctica. Predictions for the average worldwide sea rise keep changing along with the rate of ice melt. Recently, more scientists are saying the situation has worsened so that a 3-foot rise in sea level by 2100 is becoming a common theme.

But the oceans won't rise at the same rate everywhere, said study author Jianjun Yin of the Center for Ocean-Atmospheric Prediction Studies at Florida State University. It will be "greater and faster" for the Northeast, with Boston one of the worst hit among major cities, he said. So, if it's 3 feet, add another 8 inches for that region.

The explanation involves complicated ocean currents. Computer models forecast that as climate change continues, there will be a slowdown of the great ocean conveyor belt. That system moves heat energy in warm currents from the tropics to the North Atlantic and pushes the cooler, saltier water down, moving it farther south around Africa and into the Pacific. As the conveyor belt slows, so will the Gulf Stream and North Atlantic current. Those two fast-running currents have kept the Northeast's sea level unusually low because of a combination of physics and geography, Yin said.

Slow down the conveyor belt 33 to 43 percent as predicted by computer models, and the Northeast sea level rises faster, Yin said.

So far, the conveyor belt has not yet noticeably slowed.

A decade ago, scientists worried about the possibility that this current conveyor belt would halt altogether — something that would cause abrupt and catastrophic climate change like that shown in the movie "The Day After Tomorrow." But in recent years, they have concluded that a shutdown is unlikely to happen this century.

Other experts who reviewed Yin's work say it makes sense.

"Our coastlines aren't designed for that extra 8 inches of storm surge you get out of that sea level rise effect," said Jonathan Overpeck, director of an Earth studies institute at the University of Arizona.

While Boston and New York are looking at an additional 8 inches, other places wouldn't get that much extra rise. The study suggests Miami and much of the Southeast would get about 2 inches above the global sea rise average of perhaps 3 feet, and San Francisco would get less than an extra inch. Parts of southern Australia, northern Asia and southern and western South America would get less than the global average sea level rise.

This study along with another one last month looking at regional sea level rise from the projected melt of the west Antarctic ice sheet "provide a compelling argument for anticipating and preparing for higher rates of sea level rise," said Virginia Burkett, chief scientist for Global Change Research at the U.S. Geological Survey.

Burkett, who is based in Louisiana, said eventually New Englanders could be in the same "vulnerability situation" to storms and sea level rise as New Orleans.

Wall St. underwater: rising seas to hit NY hard
Marlowe Hood Yahoo News 15 Mar 09;

PARIS (AFP) – 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 (three feet) above sea level, for example, will find itself underwater more often as the 21st century unfolds, said the study, published online Sunday in Nature Geoscience.

Sea levels vary across regions by up to 24 centimetres (9.5 inches), influenced in part by powerful currents that coarse 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 59 centimetres (seven to 23 inches) 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 one metre (39 inches) 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 centimeters 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 added.

Rapid sea level increases would put cities such as New York, Boston, Baltimore and Washington D.C. 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 of around the tip of Manhattan -- included Wall Street -- would have a 10 percent chance of flooding in any given year, it concluded.