Hofer Stefan, Tedstone Andrew J, Fettweis Xavier, Bamber Jonathan L
School of Geographical Sciences, University of Bristol, Bristol, UK.
Laboratory of Climatology, Department of Geography, University of Liège, Liège, Belgium.
Sci Adv. 2017 Jun 28;3(6):e1700584. doi: 10.1126/sciadv.1700584. eCollection 2017 Jun.
The Greenland Ice Sheet (GrIS) has been losing mass at an accelerating rate since the mid-1990s. This has been due to both increased ice discharge into the ocean and melting at the surface, with the latter being the dominant contribution. This change in state has been attributed to rising temperatures and a decrease in surface albedo. We show, using satellite data and climate model output, that the abrupt reduction in surface mass balance since about 1995 can be attributed largely to a coincident trend of decreasing summer cloud cover enhancing the melt-albedo feedback. Satellite observations show that, from 1995 to 2009, summer cloud cover decreased by 0.9 ± 0.3% per year. Model output indicates that the GrIS summer melt increases by 27 ± 13 gigatons (Gt) per percent reduction in summer cloud cover, principally because of the impact of increased shortwave radiation over the low albedo ablation zone. The observed reduction in cloud cover is strongly correlated with a state shift in the North Atlantic Oscillation promoting anticyclonic conditions in summer and suggests that the enhanced surface mass loss from the GrIS is driven by synoptic-scale changes in Arctic-wide atmospheric circulation.
自20世纪90年代中期以来，格陵兰冰盖（GrIS）一直在加速流失质量。这是由于流入海洋的冰量增加以及表面融化，其中后者是主要原因。这种状态变化归因于气温上升和表面反照率降低。我们利用卫星数据和气候模型输出结果表明，自1995年左右以来，表面质量平衡的突然减少在很大程度上可归因于夏季云量减少的同时趋势增强了融冰 - 反照率反馈。卫星观测显示，从1995年到2009年，夏季云量每年减少0.9±0.3%。模型输出表明，格陵兰冰盖夏季融冰量每减少1%，夏季云量减少导致融冰量增加27±13亿吨（Gt），主要是因为低反照率消融区短波辐射增加的影响。观测到的云量减少与北大西洋涛动的状态转变密切相关，这种转变促进了夏季的反气旋条件，并表明格陵兰冰盖表面质量损失的增加是由北极范围内大气环流的天气尺度变化驱动的。
