10年12月六級真題A26-29題

Among global warming's most frightening threats is the prediction is that the polar ice-caps will melt, raising sea level so much that coastal cities from New York to Los Angles to Shanghai will be flooded. Scientists agree that key player in this scenario is the West Antarctic ice sheet, a Brazil-size mass of frozen water that is much as 7000 feet thick. Unlike floating ice shelves which have little impact on sea level when they break up, the ice sheet is anchored to bedrock will blow the sea surface. Surrounded by open ocean, it is also vulnerable, but Antarctic experts disagree strongly on just how unstable it is. Now, new evidence reveals that all or most of the Antarctic ice sheet collapsed at least once during the past 1.3 million years, a period when global temperatures probably were not significantly higher than they are today. And the ice sheet was assumed to have been stable. In geological time, a million years is recent history. The proof, which was published last week in Science, comes from a team of scientists from Uppsala University in Sweden and California Institute of Technology who drew deep holes near the edge of ice sheet. Within samples collected from the solid substances lying beneath the ice. They found fossils of microscopic marine plants which suggest that the region was once open ocean not solid ice. As Herman Engleheart, a co-author from the California Institute of Technology says, 'the West Antarctic ice sheet disappear once and can disappear again.'