英語聽力：自然百科 格陵蘭島冰原融化

As five European foreign ministers meet in Copenhagen to prepare for an aggreement to succeed the Kyoto Protocol, scientists in Greenland are warning about accelerated glacier melts. Several years ago, scientists reported that the Helheim Glacier, suddenly and without warning, had begun accelarating, spitting iceburgs ever faster into the ocean off southeastern Greenland. In just two years, it doubled the speed. Other Greenland glaciers made similar accelarations. Now, there is a bit of good news, but a lot of uncertainty. The accelarated movement has diminished, but a climate scientist who has clocked Helheim Glacier with GPS receivers for five years says there is no less concern about a collapse of Greenland's ice sheet.

Glaciers like this one here, Helheim Glacier, have accelarated their flow speed, and that's important because they are like conveyor belts that move mass out of the mid of the ice sheet and take it down to the Fjord behind us, the ocean behind us. And when they get to the end, they discharge iceburgs into the ocean and that ice displaces sea water which causes the sea level rise just the same, in the same way that melting ice in turning into the liquid water causes the sea level rise.

Helheim is a fast moving glacier flowing at around 6.5 miles per year. The extremely rapid rate of flow has slowed recently, but is still much faster than in decades past.

The Greenland ice sheet contains about seven meters of sea level equivalent. In the other words, if you were to completely get rid of the Greenland ice sheet and put all the ice that's frozen on the land surface as liquid water into the ocean, the sea levels around the world would be about seven meters higher than they are today. Now, scientists like me don't foresee a complete collapse of the ice sheet in certainly our lifetimes and probably not for a few centuries. So, that sea level, that seven meter sea levels rise scenario is not something we can expect any time soon. But let's just say that a small part of the ice sheet were to collapse and we got a rise of sea level by one meter, that would have enormous implications for societies around the world, especially the sites clustered near the coasts.

Other researchers say some but not all of Greenland's glaciers have shown similar slowdown in recent years, suggesting that a sudden dramatic increasing flow speed may not be such a cataclysmic and irregular phenomenon after all. Still, the flows remain fast enough to yield a net loss of mass from the ice sheet. And if the world continues to warm, sudden spurts of glacial acceleration may become more frequent, draining the inland ice until it eventually collapses.