The future melt of the ice sheet is no longer in doubt. However, the extent of the damage this will cause remains to be determined. A great deal of uncertainty exists with regard to climatic scenarios and modeling which makes predictions precarious. The natural variability of the climate makes it impossible to predict atmospheric circulation in summer with any certainty knowing that it is this atmospheric circulation which is the main cause of the current records  of melt. In order to model the different possible scenarios, Xavier Fettweis uses a fixed topography of the ice sheet. This does not take into account either the changes in altitude due to the melt of ice, nor ice dynamics, nor discharge from icebergs into the ocean. Knowledge about the ice sheet itself still remains very incomplete and new discoveries constantly change predictions.

As proof of the uncertainty surrounding these results, a recent American publication in the journal Nature (Harper et al., 2012) adds another decade to most of the forecasts made by Xavier Fettweis. In their study, the American researchers show the importance of the “percolation zone”. According to them, the meltwater seeps into the empty pores of the snowpack and refreezes in winter without having a direct impact on ocean levels. “In my model, I consider that if the quantity of liquid water present into the snowpack is higher than 7 %, the meltwater flows into the ocean. However, the Americans show that certain zones of the ice sheet have a much higher storage capacity than my model consider. The water which, according to my model, flows into the ocean does not immediately do so”.

In the short-term, the contribution of Greenland to the sea level rise is therefore partly compensated by the storage of water in the percolation zone. However, this discovery merely postpones the forecasts of Xavier Fettweis by around ten years. Once the storage capacity of the snow is exceeded, the meltwater will have no other possibility than to flow into the ocean, the surface of Greenland will then form one layer of impermeable ice.

A lot of unknowns remain but it is sure that the ice sheet will significantly contribute to an increase of the sea level. “All the effects are contributory factors: by melting, the ice sheet loses altitude and reheats which in turn accelerates surface melt. The snow that melts becomes salty and absorbs then more solar energy which also contributes to accelerate melt. ”, explains Xavier Fettweis. The melt of Greenland has therefore become inevitable. However, to put things into perspective: total disappearance of the ice sheet should take a lot of time. At the current rate, several hundred or even thousands of years will pass before it melts completely. Enough time for us to change our behavior?