Rising sea levels along the East Coast could mean more flooding even without superstorms
Hurricane Sandy roared up the East Coast last fall, making landfall in New Jersey on Oct. 29. Images of the raging floodwaters are hard to forget: waves rushing into the New York City subway system and the Holland Tunnel and an entire neighborhood in Queens ablaze. Sandy killed 125 people in the United States, mostly in the Northeast; caused $60 billion in damage; and displaced thousands from their homes and businesses.
Rising sea levels mean that kind of destruction could be more likely happen again—even without a superstorm like Sandy, says Andrew Kemp, an assistant professor in the Department of Earth and Ocean Sciences at Tufts.
He points to this analogy by a colleague: if you raise the floor of a basketball court, shorter players will be able to dunk the ball. Likewise, if the sea level rises, says Kemp, “a smaller storm surge the next time around could raise the flood level on a building or in your house.”
To collect data that could help predict the effects of future storms, Kemp is researching how sea levels changed in New Jersey over the past 2,000 years. He and his colleagues reconstructed sea levels from long ago by boring into salt-marsh sediment from Barnegat Bay, a 30-mile expanse of brackish water along the northern New Jersey coast. They used radiocarbon dating and other methods to examine sediment cores—long cylinders drilled into the marsh floor.
For a paper published recently in the Journal of Quaternary Science, Kemp and a fellow researcher from Rutgers University looked at seven damaging hurricanes since the late 18th century and determined that the sea level at the southern tip of Manhattan rose nearly 20 inches between a hurricane that hit in 1788 and Hurricane Sandy.
About six inches of the rise was due to the natural settling of coastal land, he says. The remainder was caused by climate change—the melting of ice-covered terrain in the Arctic and Antarctic and the thermal expansion of ocean waters as temperatures rose. As water warms, it expands, taking up more volume.
Land masses move up and down over time because of a process called glacial isostatic adjustment. Some 25,000 years ago, most of Canada and as far south as New York on the East Coast was buried under a layer of ice up to two miles thick. As the ice sheet grew and advanced southward, land along the East Coast in front of the ice margin uplifted slightly in a bulge, compensating for the weight of ice further north, like when a child steps on a seesaw. But then as the ice sheet retreated, the balance changed again, and the land mass along the East Coast subsided like the child stepping off the seesaw. “These changes in land level are an important contribution to changes in relative sea level,” says Kemp.
Relatively little is known about how sea levels changed over time—one of the goals of Kemp’s research. “We’re interested in trying to better understand the relationship between the temperature and sea level more robustly, so we can estimate sea level changes in the future,” he says. “Data from the past help to calibrate the models that we use to predict the future.”
Marjorie Howard can be reached at email@example.com.