Location map of study site. Credit: USGS

Superstorm Sandy has provided the most convincing evidence yet that powerful storms and

what are called “black swan” storms, combined with sea level rise

are pushing barrier islands out from under beach cities.

Earth scientists studying the

changes to islands of the mid-Atlantic coast and the Gulf of Mexico

announced on Monday that the islands are not disappearing, but moving

to stay in the same depth of water, which means they are shifting

landward as sea levels go up.

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Island towns facing this losing battle against the sea

are in danger of popping a real estate market bubble,

inflated by state and federal subsidies that make beach protection

and replenishment projects possible.

“This is how barrier

islands respond to sea level rise,” said Hilary Stockdon, an

oceanographer with the U.S. Geological Survey. Stockdon and her

colleagues have been building a survey of predictions of specific

changes that are likely to occur on different barrier islands, which

proved accurate for islands pummeled by Sandy.

Using before and after

images and measurements of islands like Fire Island, NY,

Stockdon and her colleagues showed that the ocean facing beaches had

been eroded away one to three meters in elevation while inland sides

of the island had gained a meter. Not only does that shift confirm

that the island is moving, but it makes the island communities more

vulnerable to even smaller storms in the future, Stockdon said at a

press conference at the meeting of the American Geophysical Union in

San Francisco.

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For decades many barrier

island beach communities managed to survive by dredging sand from

offshore and “nourishing beaches.” But political pressures have

been building to cut off government funding of such projects.

“The subsidy is slowly

being removed, so we wanted to model the effects of changes with

that,” said Dylan McNamara, an oceanographer at the University of

North Carolina Wilmington. Using his home town Ocean City Maryland as

a case study, he found that when you remove the government subsidy,

property values drop a whopping 40 percent. That bubble bursting

could be enough to cause the abandonment of some cities altogether.

The effects of the loss of the subsidy was equaled only by sea level

rise itself, said McNamara.

As for whether more such

island-shifting storms are more likely, they aren't necessarily, but

at the same time, Sandy wasn't the worst that the nature can dish

out, said Ning Lin, a civil engineer at Princeton University. She

conducted a study to see what sorts of very powerful, low probability

storms, black swan storms, are possible in New York; Darwin,

Australia and the Persian Gulf.

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Lin concluded that the

2.75-meter storm surge of Sandy in New York was not the worst that a

storm could do in that area. Rather, a full 5 meters is possible in a

true black swan storm. Though it may be little consolation to storm

Sandy survivors, “Sandy was not a black swan,” said Lin.