For Greenland, both glacier calving and surface melting contribute to mass loss. Over the last few decades surface melting has increased and now dominates over increased snowfall, leading to a positive contribution to sea level during the 21st century. For the majority of Antarctica, present and projected surface temperatures during the 21st century are too cold for significant melting to occur and precipitation is balanced by glacier flow into the ocean. (Lemke et al. 2007).
In addition to these surface processes, there are suggestions of a potential dynamical response (sliding of the outlet glaciers over the bedrock) of the Greenland and Antarctic ice sheets. In Greenland, there was a significant increase in the flow rate of many of the outlet glaciers during the early 21st century. One potential reason for this is increasing surface melt making its way to the base of the glaciers, lubricating their flow over the bed rock, consistent with increased glacier flow rates. Another effect which may be becoming more important is that, as the ice shelves around Antarctica and Greenland melt or break up (e.g. Larsen B) they allow the glaciers behind them to flow faster, leading to increased flow into the ocean.