"As the earth warms, the melting of the earth's two massive ice sheets-Antarctica and Greenland-could raise sea level enormously. If the Greenland ice sheet were to melt, it would raise sea level 7 meters. Melting of the West Antarctic Ice Sheet would raise sea level 5 meters," says Lester R. Brown, President of the Earth Policy Institute, in a recent release. "But even just partial melting of these ice sheets will have a dramatic effect on sea level rise. Senior scientists are noting that the Intergovernmental Panel on Climate Change (IPCC) projections of sea level rise during this century of 18 to 59 centimeters are already obsolete and that a rise of 2 meters during this time is within range."

Assessing the prospects for the Greenland ice sheet begins with looking at the warming of the Arctic region. A 2005 study, conducted by the Arctic Climate Impact Assessment (ACIA) team, an international group of 300 scientists, concluded that the Arctic is warming almost twice as fast as the rest of the planet. It found that in the regions surrounding the Arctic, including Alaska, western Canada, and eastern Russia, winter temperatures have already climbed by 3-4 degrees Celsius (4—7 degrees Fahrenheit) over the last half-century. In testimony before the U.S. Senate Commerce Committee, Sheila Watt-Cloutier, an Inuit speaking on behalf of the 155,000 Inuits who live in Alaska, Canada, Greenland, and the Russian Federation, described their struggle to survive in the fast-changing Arctic climate as "a snapshot of what is happening to the planet." She called the warming of the Arctic "a defining event in the history of this planet."

The ACIA report described how the retreat of the sea ice has devastating consequences for polar bears, whose very survival may be at stake. A subsequent report indicated that polar bears, struggling to survive, are turning to cannibalism. Also threatened are ice-dwelling seals, a basic food source for the Inuit.

Since this 2005 report, there is new evidence that the problem is worse than previously thought. A team of scientists from the National Snow and Ice Data Center and the National Center for Atmospheric Research concluded that the ice is melting much faster than climate models had predicted. They found that from 1979 to 2006 the summer sea ice shrinkage accelerated to 9.1 percent a decade. In 2007, Arctic sea ice shrank some 20 percent below the previous record set in 2005. This suggests that the sea could be ice-free well before 2050, the earliest date projected by the IPCC in its 2007 report. Some scientists now think that the Arctic Ocean could be ice-free in the summer by 2030, if not earlier. Arctic scientist Julienne Stroeve observed that shrinking Arctic sea ice may have reached "a tipping point that could trigger a cascade of climate change reaching into Earth's temperate regions."

Scientists are concerned that "positive feedback loops" may be starting to kick in. This term refers to a situation where a trend already under way begins to reinforce itself. One of the feedback mechanisms in the Arctic is the albedo effect. When incoming sunlight strikes the ice in the Arctic Ocean, up to 70 percent of it is reflected back into space. Only 30 percent is absorbed as heat. As the Arctic sea ice melts, however, and the incoming sunlight hits the much darker open water, only 6 percent is reflected back into space and 94 percent is converted into heat. This may account for the accelerating shrinkage of the Arctic sea ice and the rising regional temperature that directly affects the Greenland ice sheet.

For a full report, see http://www.earthpolicy.org/Books/Seg/PB3ch03_ss5.htm.

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