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From the air, the western edge of Greenland’s ice sheet looks like an aging elephant’s skin–gray and cracked, as melting at the margins exposes dirt accumulated over tens of thousands of years. A few kilometers inland, however, the gray gives way to blazing white that goes on for hundreds of miles. These vast glaciers contain snow that has fallen and compacted over millennia. The ice sheet–roughly four times the size of California, and more than three kilometers thick in places–is, in essence, a vast frozen reservoir of fresh water.

About 300 kilometers from the coast, high above the Arctic Circle, is the newest polar science station in Greenland, comprising two tents, a hut, two sledge-mounted domes, and a few vehicles. The only way to describe the location is by GPS coördinates: 77º26’54.92885” N, 51º3’19.89396” W. The station sits atop 2,500 meters of ice.

The modest encampment, manned by a nine-person scientific and support crew from a Danish-led international team, might be in the middle of nowhere, but it is also at the center of a growing effort to answer the crucial question of global warming: how quickly, and by how much, will sea levels rise? The two great polar land masses, Greenland and Antarctica, together hold nearly 99 percent of the planet’s landlocked ice, which is capable of raising sea levels when it melts (the melting of sea ice, such as that floating in the Arctic, does not raise the level of the oceans). The giant ice sheets hold enough frozen water to raise sea levels some 80 meters.

If only 10 percent of this ice melted, it would flood the world’s coasts at levels comparable to those seen in post-Katrina New Orleans. While nobody is predicting a catastrophe on that scale anytime soon, scientists are concerned that melting might greatly accelerate as the planet warms. Especially worrisome is a scenario that glaciologists and climate scientists are still piecing together: rather than slowly but steadily melting, the ice sheets could rapidly break apart. Recent observations show that some of the major glaciers on Greenland and the West Antarctic Ice Sheet are sliding ever faster seaward. But the processes involved are not well enough understood to be incorporated into the computer models used to predict how much sea levels will rise in response to climate change.

Gauging the risk that the ice sheets will break apart–and estimating how fast such a breakup would raise sea levels–will require a far better understanding of geology. Not all the bedrock beneath Greenland and Antarctica is mapped. Nobody knows how much liquid water lies under the ice; even a small amount could dramatically speed the breakup of the ice sheets by making the surface below them much more slippery. Across both land masses, scientists are striving to make more precise measurements. Some are busy installing GPS stations on the ice sheets and the bedrock surrounding the coasts to more accurately calculate loss of ice mass. Others are measuring snowfall accumulation and studying how snow compacts into ice. In this way, they are trying to estimate just how much inland ice there is–and by extension, how much has fallen into the ocean.

“We need to go right back to the drawing board on what the ice sheets are about,” says Ted Scambos, lead scientist at the National Snow and Ice Data Center at the University of Colorado at Boulder. “Fifteen years ago, we thought ice sheets wouldn’t respond quickly to global warming because the melting would happen at the surface. This was true, but what we didn’t count on was fracturing. This permits water to get to the base of the ice, all the way through the ice sheet. We were really surprised to see this even where the ice core is well below freezing. The water allows glaciers to flow more rapidly, dumping the ice into the sea.”

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Credit: David Talbot

Tagged: Energy

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