Every year, on average, the Surface Mass Balance (SMB) of Greenland increases by about 365GT.
In no year on record, (including 2012) has melting / run-off exceeded precipitation (snow and rain).
So at the moment, it is calving and melting of marine-terminating glaciers that, by being greater than SMB increase , is causing the Mass Balance of the GIS to fall.
This year Greenland melt was very high over most of the melting season, but during this time precipitation was higher than usual. This high energy weather produced an end result of about a 350 GT SMB increase - close to average. Perhaps looking at the past may not be a good way of looking at what comes next. AGW + Polar amplification, warming of the seas and reduction of winter sea ice, especially in the Baffin. More warmth, more snow, more rain? What will be the result both for SMB and melting / calving of the glaciers ?