美国科学60秒 SSS 2013-05-10（在线收听）

 　　The Arctic wasn't always covered in ice. Samples of settlement layer beneath the frozen lake show this region used to be a lot warmer and made by out in the future. The works in the general science. * gain a Russian lake 100 kilometers north of the Arctic circle contains layers of settlement than  backed to the lakes for a nation 3.6 million years ago. Now s settlement course have reviewed the back then. Summers reached about 15 to 16  degree celcius. A good 8 degrees warmer than modern Arctic summers. These warm temperatures will support the plants like TH lasted until about 2.2 million years ago.  Using the settlement core as a detailed historic climate change, scientists conceive how to forest of Arctic gradually became covered in the i snow. These changes help us to understand details about the development of v. In addition, the satellite comes from a window of time during the p epoch when greenhouse gas levels were only slightly higher than the isle today. Such sensitivity, the small c that outside changes hint at the warm Arctic future.