An uncertain future for the Greenland ice sheet
Xavier Fettweis, a researcher at the Laboratory of Climatology and Topoclimatology of the University of Liege, has been studying the Greenland ice sheet for more than 10 years in an attempt to predict fluctuations in its surface mass balance (see also Greenland: the surface of the ice sheet is melting quicker than predicted). His recent work (1) shows that melt of the ice sheet is accelerating. The year 2012 can henceforth be considered as a record year for melting. A great deal of uncertainty surrounds the future of this floating island and the consequences of the flow of meltwater into the oceans.
For 4 million years the permanence of the Greenland ice sheet has been guaranteed by snowfall that accumulates in the center of the island and which is then transformed into ice. Every year, the Greenland ice sheet gains mass in winter thanks to snowfall, and loses mass in summer due to surface melt and discharge from icebergs into the ocean. In spite of the increase of melt, the annual surface mass balance of the ice sheet, that is to say the difference between the gains (snowfall) and the losses (melt) of the surface, remains positive. The interior and the peaks of the ice sheet - the “accumulation zone”- continue to gain mass thanks to snowfall which is greater than the summer melt. On the contrary, the edges of the ice sheet which are lower in altitude tend to be worn away rapidly. In this “ablation zone”, the mass lost by melting is continuously increasing. In summer, once the winter snow has disappeared, bare ice appears, which increases surface melt even more because it is less white than the snow and thus absorbs more infrared radiation. The surface mass balance is therefore in deficit. In spite of the extension of the melt zone, the Greenland ice sheet remains balanced thanks to ice dynamics which redistributes the snow mass accumulated in the center to the edges of the ice sheet.
(1) Fettweis, X., Franco, B., Tedesco, M., van Angelen, J. H., Lenaerts, J. T. M., van den Broeke, M. R., and Gallée, H.: Estimating Greenland ice sheet surface mass balance contribution to future sea level rise using the regional atmospheric climate model MAR, The Cryosphere Discuss., 6, 3101-3147, doi:10.5194/tcd-6-3101-2012, 2012a.
Fettweis, X., Hanna, E., Lang, C., Belleflamme, A., Erpicum, M., and Gallée, H.: Brief communication "Important role of the mid-tropospheric atmospheric circulation in the recent surface melt increase over the Greenland ice sheet", The Cryosphere Discuss., 6, 4101-4122, doi:10.5194/tcd-6-4101-2012, 2012b.
Harper, J., Humphrey, N., Pfeffer, W.T., Brown1 J. and X. Fettweis, Greenland Ice Sheet Contribution to Sea Level Rise Buffered by Meltwater Storage in Firn, Nature, doi: 10.1038/nature11566, 2012.