May 28, 2009

US Sea Levels May Rise More As Greenland’s Glaciers Melt

Scientists say that a number of the United States' most populous east coast cities "” including New York and Boston "” could see higher than expected rises in sea levels if Greenland's glacial-melt continues at its current rate.

Researchers reported that sea levels on North America's northeast coast could potentially rise by 12 to 20 inches more than other coastal regions if the melting of Greenland's ice sheet continues to accelerate.

Because of the tremendous quantity of fresh water released into the northern Atlantic Ocean, patterns of oceanic water circulation "” known in the science community as meridional overturning circulation "” could be temporarily or permanently altered.

"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...Major northeastern cities are directly in the path of the greatest rise," explained Aixie Hu, lead author of the recent article published at the National Center for Atmospheric Research in Boulder, Colorado.

The assessment offered in this report is significantly more severe than those offered by previous studies which had predicted rising sea levels of less than 10 inches.

Earlier studies, however, such as the one published in March in the journal Nature Geoscience, failed to factor in the effects of Greenland's melting ice sheets.  The new study predicts that this could direct an additional 4 to 12 inches of water toward North America's northeastern coast in additional to generally rising global sea levels.

In answer to e-mail questions, Hu stated that this could potentially put residents of coastal metropolises like New York, Boston and Halifax in danger of a number of unwelcome side effects.

The most clear and present threat would be increased risk of flooding, but Hu added that drainage systems would also be compromised as salty ocean water backed-up into river deltas and damaged already frail ecosystems.

"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 also wrote.  Cities that already have marginal problems with subsidence, or sinking ground, would very likely begin to see a number of greater complications.

There is general consensus among climatologists that Greenland's ice sheets are melting much faster as a result of global climate change, which in turn causes global sea levels to rise. 

Sea levels, however, do not rise at the same rate around the planet.  The North Atlantic, for example, is currently 28 inches lower that the North Pacific, because the Atlantic Ocean has a dense layer of deep, cold water that is not present in the Pacific.

"The oceans will not rise uniformly as the world warms," said Gerald Meehl, a co-author of the paper. "Ocean dynamics will push water in certain directions, so some locations will experience sea level rise that is larger than the global average."

The rate at which Greenland's ice is melting has steadily accelerated by roughly 7 percent a year for each of the last 12 years, said Hu.  This pattern, however, is unlikely to continue for much longer.

Unlikely, but not impossible, said Hu. 

As the current levels of carbon dioxide emissions continue to exceed the numbers projected by the UN's Intergovernmental Panel on Climate change, it may be possible that the 7 percent annual increase could indeed continue over the next 50 years, potentially resulting in a worst-case scenario.


Image 1: An aerial view of Long Island shows its low-lying shores, vulnerable to sea-level rise effects. Credit: New York State Department of Environmental Conservation

Image 2: This map shows projected sea-level rise; the bar at the bottom is in centimeters. Credit: NCAR

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