Aerial view of Seaside Heights after Hurricane Sandy. Photo: George Steinmetz / National Geographic

By Tim Folger
1 September 2013

(National Geographic) – By the time Hurricane Sandy veered toward the Northeast coast of the United States last October 29, it had mauled several countries in the Caribbean and left dozens dead. Faced with the largest storm ever spawned over the Atlantic, New York and other cities ordered mandatory evacuations of low-lying areas. Not everyone complied. Those who chose to ride out Sandy got a preview of the future, in which a warmer world will lead to inexorably rising seas.

Brandon d’Leo, a 43-year-old sculptor and surfer, lives on the Rockaway Peninsula, a narrow, densely populated, 11-mile-long sandy strip that juts from the western end of Long Island. Like many of his neighbors, d’Leo had remained at home through Hurricane Irene the year before. “When they told us the tidal surge from this storm would be worse, I wasn’t afraid,” he says. That would soon change.

D’Leo rents a second-floor apartment in a three-story house across the street from the beach on the peninsula’s southern shore. At about 3:30 in the afternoon he went outside. Waves were crashing against the five-and-a-half-mile-long boardwalk. “Water had already begun to breach the boardwalk,” he says. “I thought, Wow, we still have four and a half hours until high tide. In ten minutes the water probably came ten feet closer to the street.”

Back in his apartment, d’Leo and a neighbor, Davina Grincevicius, watched the sea as wind-driven rain pelted the sliding glass door of his living room. His landlord, fearing the house might flood, had shut off the electricity. As darkness fell, Grincevicius saw something alarming. “I think the boardwalk just moved,” she said. Within minutes another surge of water lifted the boardwalk again. It began to snap apart.

Three large sections of the boardwalk smashed against two pine trees in front of d’Leo’s apartment. The street had become a four-foot-deep river, as wave after wave poured water onto the peninsula. Cars began to float in the churning water, their wailing alarms adding to the cacophony of wind, rushing water, and cracking wood. A bobbing red Mini Cooper, its headlights flashing, became wedged against one of the pine trees in the front yard. To the west the sky lit up with what looked like fireworks—electrical transformers were exploding in Breezy Point, a neighborhood near the tip of the peninsula. More than one hundred homes there burned to the ground that night.

The trees in the front yard saved d’Leo’s house, and maybe the lives of everyone inside—d’Leo, Grincevicius, and two elderly women who lived in an apartment downstairs. “There was no option to get out,” d’Leo says. “I have six surfboards in my apartment, and I was thinking, if anything comes through the wall, I’ll try to get everyone on those boards and try to get up the block. But if we’d had to get in that water, it wouldn’t have been good.”

After a fitful night’s sleep d’Leo went outside shortly before sunrise. The water had receded, but thigh-deep pools still filled parts of some streets. “Everything was covered with sand,” he says. “It looked like another planet.”

A profoundly altered planet is what our fossil-fuel-driven civilization is creating, a planet where Sandy-scale flooding will become more common and more destructive for the world’s coastal cities. By releasing carbon dioxide and other heat-trapping gases into the atmosphere, we have warmed the Earth by more than a full degree Fahrenheit over the past century and raised sea level by about eight inches. Even if we stopped burning all fossil fuels tomorrow, the existing greenhouse gases would continue to warm the Earth for centuries. We have irreversibly committed future generations to a hotter world and rising seas.

In May the concentration of carbon dioxide in the atmosphere reached 400 parts per million, the highest since three million years ago. Sea levels then may have been as much as 65 feet above today’s; the Northern Hemisphere was largely ice free year-round. It would take centuries for the oceans to reach such catastrophic heights again, and much depends on whether we manage to limit future greenhouse gas emissions. In the short term scientists are still uncertain about how fast and how high seas will rise. Estimates have repeatedly been too conservative.

Global warming affects sea level in two ways. About a third of its current rise comes from thermal expansion—from the fact that water grows in volume as it warms. The rest comes from the melting of ice on land. So far it’s been mostly mountain glaciers, but the big concern for the future is the giant ice sheets in Greenland and Antarctica. Six years ago the Intergovernmental Panel on Climate Change (IPCC) issued a report predicting a maximum of 23 inches of sea-level rise by the end of this century. But that report intentionally omitted the possibility that the ice sheets might flow more rapidly into the sea, on the grounds that the physics of that process was poorly understood.

As the IPCC prepares to issue a new report this fall, in which the sea-level forecast is expected to be slightly higher, gaps in ice-sheet science remain. But climate scientists now estimate that Greenland and Antarctica combined have lost on average about 50 cubic miles of ice each year since 1992—roughly 200 billion metric tons of ice annually. Many think sea level will be at least three feet higher than today by 2100. Even that figure might be too low.

“In the last several years we’ve observed accelerated melting of the ice sheets in Greenland and West Antarctica,” says Radley Horton, a research scientist at Columbia University’s Earth Institute in New York City. “The concern is that if the acceleration continues, by the time we get to the end of the 21st century, we could see sea-level rise of as much as six feet globally instead of two to three feet.” Last year an expert panel convened by the National Oceanic and Atmospheric Administration adopted 6.6 feet (two meters) as its highest of four scenarios for 2100. The U.S. Army Corps of Engineers recommends that planners consider a high scenario of five feet.

One of the biggest wild cards in all sea-level-rise scenarios is the massive Thwaites Glacier in West Antarctica. Four years ago NASA sponsored a series of flights over the region that used ice-penetrating radar to map the seafloor topography. The flights revealed that a 2,000-foot-high undersea ridge holds the Thwaites Glacier in place, slowing its slide into the sea. A rising sea could allow more water to seep between ridge and glacier and eventually unmoor it. But no one knows when or if that will happen.

“That’s one place I’m really nervous about,” says Richard Alley, a glaciologist at Penn State University and an author of the last IPCC report. “It involves the physics of ice fracture that we really don’t understand.” If the Thwaites Glacier breaks free from its rocky berth, that would liberate enough ice to raise sea level by three meters—nearly ten feet. “The odds are in our favor that it won’t put three meters in the ocean in the next century,” says Alley. “But we can’t absolutely guarantee that. There’s at least some chance that something very nasty will happen.” [more]

Rising Seas

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