Variability Change and Anthropogenic Signal Emergence in Greenland Surface Mass Balance

Tuesday, May 13, 2014 - 07:00
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ABSTRACT FOR ORAL PRESENTATION (PREFERABLY): The Greenland Ice Sheet (GrIS) surface mass balance (SMB, the amount of ice gained or lost by the ice sheet over a year) is expected to trend downwards drastically under anthropogenically-forced climate change. Superimposed on this long-term trend will be SMB variability which reflects snowfall and melt variability over the ice sheet. This SMB variability will have an impact on ice dynamics, ocean circulation, and sea level rise rates. For the first time, we investigated long term trends to GrIS SMB variability, using a CESM simulation from 1850 and 2100 under historical and RCP8.5 forcing. We found a large and significant GrIS SMB variability increase in response to anthropogenic forcing, and attributed this increase primarily to expansion of the high-variability ablation areas, and secondarily to increases in accumulation area and ablation area specific SMB. Additionally, we explored the role of SMB variability in regulating the ongoing emergence of an anthropogenic signature in GrIS SMB. Using a signal-to-noise approach, we found that the spatial pattern of variability, combined with the spatial pattern of GrIS SMB change, will likely result in the emergence of an anthropogenic signal in GrIS SMB with approximately the same timing in both the deep ice sheet interior and the ice sheet margins. However, the emergence signal in these two regions is of opposite sign, with interior emergence occurring due to small increases in snowfall against a background of low SMB variability, and margin emergence occurring due to large melt increases against a backdrop of high SMB variability. These findings suggest that, perhaps counterintuitively, the summit of Greenland may be an excellent location to directly monitor the effect of anthropogenic forcing on the climate system.