Topic 1 (选题一)

　　In Greenland, Ice and Instability

　　The ancient frozen dome cloaking Greenland is so vast that pilots have crashed into what they thought was a cloud bank spanning the horizon. Flying over it, you can scarcely imagine that it could erode fast enough to dangerously raise sea levels any time soon.

　　Along the flanks in spring and summer, however, the picture is very different. For an increasing number of warm years, a network of blue lakes and rivulets of melt-water has been spreading ever higher on the icecap.

　　The melting surface darkens, absorbing up to four times as much energy from the sun as snow, which reflects sunlight. Natural drainpipes called moulins carry water from the surface into the depths, in some places reaching bedrock.

　　The process slightly, but measurably, lubricates and accelerates the grinding passage of ice towards the sea.

　　Most important, many glaciologists say, is the break-up of huge semi-submerged clots of ice where some large Greenland glaciers, particularly along the west coast, squeeze through fiords as they meet the warming ocean. As these passages have cleared, this has sharply accelerated the flow of many of these creeping, corrugated and frozen rivers.

　　Some glaciologists fear that the rise in seas in a warming world could be much greater than the upper estimate of about 60 centimeters this century made by the Intergovernmental Panel on Climate Change last year. (Seas rose less than 30 centimeters last century.)

　　The panel's assessment did not include factors known to contribute to ice flows but not understood well enough to estimate with confidence. SCIENTIFIC scramble is under way to clarify whether the erosion of the world's most vulnerable ice sheets, in Greenland and west Antarctica, can continue to accelerate. The effort involves field and satellite analyses and sifting for clues from past warm periods,

　　Things are definitely far more serious than anyone would have thought five years ago.