Deborah Zabarenko, PlanetArk 28 May 09;
WASHINGTON - New York, Boston and other cities on North America's northeast coast could face a rise in sea level this century that would exceed forecasts for the rest of the planet if Greenland's ice sheet keeps melting as fast as it is now, researchers said on Wednesday.
Sea levels off the northeast coast of North America could rise by 12 to 20 inches more than other coastal areas if the Greenland glacier-melt continues to accelerate at its present pace, the researchers reported.
This is because the current rate of ice-melting in Greenland could send so much fresh water into the salty north Atlantic Ocean that it could change the vast ocean circulation pattern sometimes called the conveyor belt. Scientists call this pattern the meridional overturning circulation.
"If the Greenland melt continues to accelerate, we could see significant impacts this century on the northeast U.S. coast from the resulting sea level rise," said Aixie Hu, lead author of an article on the subject in the journal Geophysical Research Letters.
"Major northeastern cities are directly in the path of the greatest rise," said Hu, a scientist at the National Center for Atmospheric Research in Boulder, Colorado.
This is an even bleaker assessment than an earlier study indicated. A March article in the journal Nature Geoscience said warmer water temperatures could shift ocean currents so as to raise sea levels off the U.S. northeast coast by about 8 inches more than the average global sea level rise.
NOT LIKELY BUT POSSIBLE
However, this earlier research did not include the impact of melting Greenland ice, which would speed changes in ocean circulation and send 4 to 12 more inches of water toward northeastern North America, on top of the average global sea level rise.
That could put residents of New York, Boston and Halifax, Nova Scotia, at risk since these cities and others lie close to sea level now, Hu said in answer to e-mailed questions.
Not only would coastal residents be at direct risk from flooding but drainage systems would suffer as salty ocean water would move back into river deltas, changing the biological environment, Hu wrote in an e-mail.
"In a flooding zone, because the higher sea level may impede the function of the drainage system, the future flood may become more severe," he wrote. If cities are prone to subsidence -- where the ground sinks -- higher sea levels would also make that problem worse, according to Hu.
The ice that covers much of Greenland is melting faster now due to global climate change, raising world sea levels. But sea level does not rise evenly around the globe. Sea level in the North Atlantic is now 28 inches lower than in the North Pacific, because the Atlantic has a dense, compact layer of deep, cold water that the Pacific lacks.
Greenland's ice-melt rate has increased by 7 percent a year since 1996 but Hu said it is unlikely to continue. Still, he and his co-authors ran computer simulations that included this fast-paced melting, along with more moderate scenarios with ice-melt increasing by 3 percent or 1 percent annually.
Hu said it was hard to say whether the 7 percent annual increase could go on for the next 50 years but said it was possible since the current rate of increase in climate-warming carbon dioxide is higher than the high end of projections by the U.N. Intergovernmental Panel on Climate Change.
(Editing by Bill Trott)
Sea’s Rise May Prove the Greater in Northeast
Cornelia Dean, New York Times 27 May 09;
In the debate over global warming, one thing is clear: as the planet gets warmer, sea levels will rise. But how much, where and how soon? Those questions are notoriously hard to answer.
Scientists at the National Center for Atmospheric Research, in Boulder, Colo., are now adding to the complexity with a new prediction. If the melting of Greenland’s ice sheets continues to accelerate, they say, sea levels will rise even more in the northeastern United States and Maritime Canada than in other areas around the world.
The researchers, Aixue Hu and Gerald A. Meehl, based their predictions on runoff data from Greenland and an analysis of ocean circulation patterns.
They said that if Greenland melting continued to accelerate, it would alter ocean currents in a way that sends warmer water toward the northeastern and Maritime coasts. Because water expands as it warms, this influx of warmer water would raise sea levels as much as a foot or two more than in other coastal regions by the end of the century.
The researchers are reporting their findings Friday in Geophysical Research Letters, a publication of the American Geophysical Union. Their report comes two weeks after other researchers predicted that climate-related ice shifts at the South Pole would raise sea levels on the east and west coasts of North America by yet an additional 1.5 feet.
These rises in sea level, if they occur, would be on top of an overall increase of one to two feet predicted by 2100 as a result of global warming. That prediction, by the Intergovernmental Panel on Climate Change, a United Nations body, was rendered in a 2007 report that more or less ignored the question of melting glaciers and ice sheets because the process is so hard to forecast. As a result, many researchers regard the prediction as unrealistically optimistic.
The flooding potential of sea level rise depends in part on coastal topography. In places where the coast slopes gently, a rise of a few feet could send ocean waters 100 feet inland or more.
In recent years, Greenland melt rates have been increasing by 7 percent a year, the researchers said. If that continues, they said, the northeastern and Maritime Canadian coasts can expect almost two feet of additional sea level rise by 2100.
They said it was more likely that the melting would accelerate at a rate of only about 3 percent a year. In that event, they said, the region can expect an additional one foot of sea level rise.
NYC, Boston Could See Higher Sea Level Rise
Andrea Thompson, livescience.com Yahoo News 27 May 09;
New York, Boston, Halifax and other cities in the northeastern United States and Canada could come under greater threat from sea level rise due to melting of the Greenland ice sheet this century, a new study suggests.
Greenland is the world's largest island, covering an area more than three times the size of Texas. Some 81 percent of it has been permanently capped by ice, with many glaciers that slowly move ice out sea.
The new study, detailed in the May 29 issue of the journal Geophysical Research Letters, finds that if Greenland's ice melts at moderate to high rates, ocean circulation by 2100 may shift and cause sea levels off the northeast coast of North America to rise by about 12 to 20 inches (about 30 to 50 centimeters) more than in other coastal areas.
"If the Greenland melt continues to accelerate, we could see significant impacts this century on the northeast U.S. coast from the resulting sea level rise," said study author Aixue Hu, of the National Center for Atmospheric Research (NCAR). "Major northeastern cities are directly in the path of the greatest rise."
Other recent studies have also pointed to the peril that sea level rise might hold for North America. A March study in the journal Nature Geoscience warned that warmer water temperatures could shift ocean currents in a way that would raise sea levels off the Northeast by about 8 inches (20 cm) more than the average global sea level rise.
But that study did not include the additional impact of Greenland's ice, which at moderate to high melt rates would further accelerate changes in ocean circulation and drive an additional 4 to 12 inches (about 10 to 30 cm) of water toward heavily populated areas in northeastern North America on top of average global sea level rise. More remote areas in extreme northeastern Canada and Greenland could see even higher sea level rise.
"The oceans will not rise uniformly as the world warms," said study co-author Gerald Meehl, also of NCAR. "Ocean dynamics will push water in certain directions, so some locations will experience sea level rise that is larger than the global average."
The 2007 assessment of the Intergovernmental Panel on Climate Change (IPCC) projected that sea levels worldwide could rise by an average of 7 to 23 inches (18 to 59 cm) this century. However, many researchers now think the rise will be greater because of dynamic factors in ice sheets that appear to have accelerated the melting rate in recent years.
To estimate the impact of Greenland ice melt on ocean circulation, Hu and his colleagues used a computer model that simulates global climate. They considered three scenarios: the melt rate continuing to increase by 7 percent per year, as has been the case in recent years, or the melt rate slowing down to an increase of either 1 or 3 percent per year.
They found that the change in sea level rise would be lowest at the 1 percent rate, but would still raise levels more than in the previous Nature Geoscience study. Sea level change would be greatest for the 7 percent scenario, which is not surprising, but Hu cautioned that other modeling studies have indicated that this scenario is unlikely.
The new research was funded by the U.S. Department of Energy and by NCAR's sponsor, the National Science Foundation.
