New York Flood Risk to Grow as Weaker Currents Raise Sea Level

By Alex Morales
March 16

(Bloomberg) -- The Big Apple faces a greater flood risk over the next century as weaker Atlantic currents raise sea levels on the U.S. East Coast by more than in London or Tokyo.

Global warming will alter Atlantic Ocean circulation in a way that will move more water to New York by 2100, Florida State University-led scientists said in a study in Nature Geoscience today. Including the expansion of water as it warms, the total gain may be 51 centimeters (20 inches), they said, not counting effects of melting ice sheets in Greenland and Antarctica.

Low-lying nations such as the Maldives, Bangladesh and Tuvalu aren?t alone in facing risks posed by rising seas, the research indicated. U.S. centers of economy, politics and education in the northeast also have to face up to the threat, said Jianjun Yin, the study?s lead author.

?This important region will experience some of the fastest and largest sea level rises this century,? Yin said in a phone interview from Tallahassee, Florida. That will put New York, Boston and Washington more at risk from flooding and storm surges, he said.

New York authorities have already begun looking at impacts of climate change on the city, which is an average of 5 meters above sea level. Last month, the city?s panel on climate change published a report saying sea levels could rise 12 to 23 inches this century, and emphasizing the need to adapt infrastructure.

The ocean level isn?t uniform across the ocean. Water circulation in the Atlantic serves to keep seas relatively lower along the U.S. East Coast. The system of currents, called the Atlantic meridional overturning circulation, channels the warm Gulf Stream to the northeast and moves colder, deeper waters southwards. Its effect of lowering U.S. sea levels will be dimmed as warming slows the currents, Yin?s team said.

Melting Ice

The process is similar to mixing hot and cold water in a bathtub by moving it around with your hand, according to Katherine Richardson, professor of Oceanography at the University of Copenhagen.

?When you slosh the water around, you create currents and you can see that the water?s higher at some parts than others,? Richardson said in a telephone interview. ?When you change currents you change sea levels in some areas more than others.?

Richardson last week chaired a meeting of 2,500 researchers in Copenhagen to discuss the latest climate change science. Research unveiled there showed average sea levels this century may rise than more than a meter because of faster-than-expected ice-melt in Greenland and Antarctica. That?s more than the 18- to-59-centimeter increase forecast in 2007 by the United Nations.

Low Estimates

Yin?s team examined different scenarios for emissions of heat-trapping greenhouse gases, the main driver blamed for global warming. They found that even for a low future emissions scenario, slower currents produced 36 centimeters of sea level gain at New York, 37 centimeters in Boston and 33 in Washington, including the effect of expanding waters. With high emissions, the increases were 51, 52 and 44 centimeters for the three cities.

Higher temperatures serve to slow the Atlantic?s currents because they cause sea ice, glaciers and ice sheets to melt, reducing the surface salinity and lessening the ability of shallower waters to sink and circulate back south, according to the U.K.?s National Oceanography Centre in Southampton.

?We do expect the meridional overturning circulation to slow down over the next 50 to 100 years? as a result of global warming, Stuart Cunningham, who researches ocean currents at the centre, said in a telephone interview. ?The general principal of slower currents leading to sea-level change is well known, but there haven?t been many specific modeling studies.?

?Take Action?

The effect of the changes in currents alone in New York would add 26 centimeters to local sea levels, assuming greenhouse gas emissions follow a ?medium? trajectory, according to the paper. That compares with rises of about 6 centimeters in Miami, 2 in San Francisco and Cape Town, 12 in London and 7 in Tokyo and Sydney, Yin said. He didn?t have figures for Bangladesh and Pacific and Indian Ocean islands.

?Climate change is real and could have serious consequences for New York if we don?t take action,? New York Mayor Michael Bloomberg said in a Feb. 17 statement. ?We cannot wait until after our infrastructure has been compromised to begin to plan for the effects of climate change now.?

The mayor is founder and majority owner of Bloomberg News parent Bloomberg LP.

To contact the reporter on this story: Alex Morales in London at amorales2@bloomberg.net.
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