Greenland Ice Sheet “Sliding” Likely to be a Small Contributor to Future Sea Level Rise
A warming climate is expected to melt large portions of the Greenland and Antarctic ice sheets, contributing to sea level rise. However, since the behavior of ice sheets as they melt is poorly known, it is difficult to estimate how soon major changes will occur. Important melting behaviors in the Greenland ice sheet include surface melting, iceberg breakoff from around the edges, and enhanced sliding as meltwater slips through cracks to the bedrock lubricating ice sheet slippage into the sea. The last of these factors, lubrication, was carefully estimated in a recent study by scientists from multiple institutions, including U.S. Department of Energy researchers from Los Alamos National Laboratory. A wide range of observations suggest that water generated by melt at the ice sheet’s surface reaches the bed by both fracture and drainage through moulins (roughly circular, vertical to nearly vertical well-like shafts within a glacier through which water enters from the surface). However, the observations are insufficient to determine whether the water enhances ice flow. The research team performed a modeling analysis, varying the flow formulations to find two contrasting possibilities: continuously increasing or bounded changes in lubrication and glacier speed with increased meltwater input. These contrasting scenarios were applied to four sophisticated ice sheet models in a series of experiments for a warmer future scenario, forced by changes in likely ice sheet surface mass changes, lubrication changes, and a combination of these factors. The team determined that the additional sea level rise brought about by lubrication is small (= 8 mm) in comparison with that from experiments forced only by changes in surface mass balance (~170 mm). Although changes in lubrication generate widespread effects on the flow and form of the ice sheet, they do not substantially affect net mass loss. These experiments predict that by year 2200, increases in the ice sheet’s contribution to sea level rise from basal lubrication will be no more than 5% of the contribution from surface mass budget forcing alone.
Shannon, S. R., A. J. Payne, I. D. Bartholomew, M. R. van den Broeke, T. L. Edwards, X. Fettweis, O. Gagliardini, F. Gillet-Chaulet, H. Goelzer, M. J. Hoffman, P. Huybrechts, D. W. F. Mair, P. W. Nienow, M. Perego, S. F. Price, C. J. P. Paul Smeets, A. J. Sole, R. S. W. van de Wal, and T. Zwinger. 2013. “Enhanced Basal Lubrication and the Contribution of the Greenland Ice Sheet to Future Sea Level Rise,” Proceedings of the National Academy of Sciences (USA), DOI:10.1073/pnas.1212647110.