NYC, Boston Could See Higher Sea Level Rise

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.

• Video – Learn How Ice Melts
• Mystery of Greenland's Ice Lingers as Sheet Shrinks
• Antarctic Meltdown Would Flood Washington, D.C.