Background
The authors write that "changes to the dynamics of the Greenland ice sheet can be forced by various mechanisms including surface-melt-induced ice acceleration and oceanic forcing of marine-terminating glaciers." And they note, in this regard, that "during summer, meltwater generated on the Greenland ice sheet surface accesses the ice sheet bed, lubricating basal motion and resulting in periods of faster ice flow." However, they say that "the net impact of varying meltwater volumes upon seasonal and annual ice flow, and thus sea level rise, remains unclear."

What was done
In an effort to bring some clarity to this situation, Tedstone et al. used "observations of ice motion to examine the surface melt-induced dynamic response of a land-terminating outlet glacier in southwest Greenland to the exceptional melting observed in 2012," when on 12 July of that year 98.6% of the Greenland ice sheet experienced melting (the most significant melt event since 1889), and when one week later 79.2% of the ice sheet melted and summer ice sheet runoff was ~3.9σ above the 1958-2011 mean, which mean value had been matched most recently in 2009.

What was learned
The seven scientists determined that despite the record summer melting of 2012, subsequent reduced winter ice motion resulted in 6% less net annual ice motion in 2012 than in the average year of 2009.

What it means
In the final sentence of their paper's abstract, Tedstone et al. say their findings suggest that "surface melt-induced acceleration of land-terminating regions of the ice sheet will remain insignificant even under extreme melting scenarios," taking a good deal of the wind out of the sails of the world's climate alarmists.