雅思阅读材料：气候变暖下挣扎的北极熊_雅思英语阅读

雅思阅读材料：气候变暖下挣扎的北极熊

　　For survival, the bears do not just need sea ice to walk about on. There have to be prey for them to eat as well. It so happens, says Brendan Kelly of the National Marine Mammal Laboratory in Alaska, that the ringed seals and bearded seals which polar bears specialise in catching will be all too happy to live in the refuge. An important requirement for seals is thick snow cover in the spring, to dig lairs in. These lairs protect them and their young from the cold and make it harder for polar bears to spot them. Climate models generally predict more snow as the temperature rises, but much of it, says Dr Kelly, will fall in the autumn on a sea that has not yet frozen over. The refuge will be the only place in the Arctic where a lack of snow will not be an issue.

　　The sea mammals and their hunters would have even fewer problems if fears of climatic feedback in the Arctic proved unfounded. The paper in Nature claims that they are. A group led by Steven Amstrup of the US Geological Surveys Alaska Science Centre ran CCSM3 with several assumptions about reducing greenhouse gases. Dr Amstrup concluded that although the sea ice does shrink, it does so gradually and in proportion to the temperature rises that result. Sudden disappearances of ice do occur, but the Arctic seems able to recover from them. This is important, as it will give humanity more time to reduce its emissions and it improves, among many other things, the chance that polar bears will survive as a species.