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Published June 9, 2008 08:34 AM

Why Are Rising Sea Levels a Threat?

Dear EarthTalk: Recent NASA photos showed the opening of the Northwest Passage and that a third of the Arctic’s sea ice has melted in recent. Are sea levels already starting to rise accordingly, and if so what effects is this having?                                       -- Dudley Robinson, Ireland

Researchers were astounded when, in the fall of 2007, they discovered that the year-round ice pack in the Arctic Ocean had lost some 20 percent of its mass in just two years, setting a new record low since satellite imagery began documenting the terrain in 1978. Without action to stave off climate change, some scientists believe that, at that rate, all of the year-round ice in the Arctic could be gone by as early as 2030.

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This massive reduction has allowed an ice-free shipping lane to open through the fabled Northwest Passage along northern Canada, Alaska and Greenland. While the shipping industry—which now has easy northern access between the Atlantic and Pacific oceans—may be cheering this “natural” development, scientists worry about the impact of the resulting rise in sea levels around the world.

With about a third of the world’s population—and 25 percent of Americans—living within 300 feet of an ocean coastline, sea level rise is a big deal. According to the Intergovernmental Panel on Climate Change, made up of leading climate scientists, sea levels have risen some 3.1 millimeters per year since 1993.

The World Wildlife Fund (WWF) reports that low-lying island nations, especially in equatorial regions, have been hardest hit by this phenomenon, and some are threatened with total disappearance. Rising seas have already swallowed up two uninhabited islands in the Central Pacific. On Samoa, thousands of residents have moved to higher ground as shorelines have retreated by as much as 160 feet. And islanders on Tuvalu are scrambling to find new homes as salt water intrusion has made their groundwater undrinkable while increasingly strong hurricanes and ocean swells have devastated shoreline structures.

WWF says that rising seas throughout tropical and sub-tropical regions of the world have inundated coastal ecosystems, decimating local plant and wildlife populations. In Bangladesh and Thailand, coastal mangrove forests—important buffers against storms and tidal waves—are giving way to ocean water.

Unfortunately, even if we curb global warming emissions today, these problems are likely to get worse before they get better. According to marine geophysicist Robin Bell of Columbia University’s Earth Institute, sea levels rise by about 1/16” for every 150 cubic miles of ice that melts off one of the poles.

“That may not sound like a lot, but consider the volume of ice now locked up in the planet’s three greatest ice sheets,” she writes in a recent issue of Scientific American. “If the West Antarctic ice sheet were to disappear, sea level would rise almost 19 feet; the ice in the Greenland ice sheet could add 24 feet to that; and the East Antarctic ice sheet could add yet another 170 feet to the level of the world’s oceans: more than 213 feet in all.” Bell underscores the severity of the situation by pointing out that the 150-foot tall Statue of Liberty could be completely submerged within a matter of decades.

CONTACTS: Intergovernmental Panel on Climate Change (IPCC), www.ipcc.ch; WWF, www.panda.org; Earth Institute at Columbia University, www.earth.columbia.edu.

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