The melting of the Greenland Ice Sheet this century may drive more water than previously thought toward the already threatened coastlines of New York, Boston, Halifax and other cities in the northeastern United States and Canada, according to new research led by the U.S. National Center for Atmospheric Research (NCAR).

Results of the study are being published Friday in Geophysical Research Letters. They suggest that moderate to high rates of ice melt from Greenland may shift ocean circulation by about 2100, causing sea levels off the northeast coast of North America to rise by about 30 to 51 centimeters more than other coastal areas.

The research builds on recent reports that have found that sea level rise could adversely affect North America, and its findings suggest that the situation is even more urgent than previously believed.

"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," says scientist Aixue Hu, the paper' s lead author. Hu is at the NCAR in Boulder, Colorado. "Major northeastern cities are directly in the path of the greatest rise. "

A study in Nature Geoscience in March warned that warmer water temperatures could shift ocean currents in a way that would raise sea levels off the Northeast by about eight inches more than the average global sea level rise that is expected with global warming.

But it did not include the additional impact of Greenland ice, which at moderate to high melt rates would further accelerate changes in ocean circulation and drive an additional 10 to 30 centimeters of water toward northeastern North America on top of the average global rise.

The new research was funded by the U.S. Department of Energy and by NCAR's sponsor, the National Science Foundation (NSF). It was conducted by scientists at NCAR, the University of Colorado at Boulder, and Florida State University.

The northeast coast of North America is especially vulnerable to the effects of Greenland ice melt because of the way the meridional overturning circulation acts like a conveyer belt transporting water through the Atlantic Ocean.

The circulation carries warm Atlantic water from the tropics to the north, where it cools and descends to create a dense layer of cold water. As a result, sea level is currently about 71 centimeters lower in the North Atlantic than the North Pacific, which lacks such a dense layer.

If the melting of the Greenland Ice Sheet were to increase by 3 percent or 7 percent yearly, the additional fresh water could partially disrupt the northward conveyor belt.

This would reduce the accumulation of deep, dense water. Instead, the deep water would be slightly warmer, expanding and elevating the surface across portions of the north Atlantic.

"The oceans will not rise uniformly as the world warms," says NCAR scientist 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."