How hard is it to melt the Greenland Ice Sheet?

The Greenland Ice is a geographic oddity.  While the West and East Antarctic Ice Sheets are as far south as you can get and securely nestle up to the South Pole, the Greenland Ice Sheet is a small, solitary ice sheet that extends southward to 60° N. Latitude.  Extensive areas of North America, Europe and Asia lie farther north, but are not ice covered today.  Entire countries like Norway and Sweden are as far north as Greenland, and my own University here in Alaska is at the same latitude as the middle of the Greenland Ice Sheet.     Only 15,000 years ago there were huge ice sheets over the parts of North America right next to the Greenland Ice Sheet, but those ice sheets melted when the ice age ended while the Greenland Ice Sheet hung on.  It doesn't take much more than a glance at a globe to make one wonder...how hard would it be to melt the Greenland Ice Sheet now.

We may be about to find out.  Field studies and satellite surveys all agree that Greenland is currently melting fast.   The most recent measurements indicate Global sea level is rising at about 3.5 mm per year,  and almost all of the rise in global sea level seems to be coming water melting from the Greenland Ice Sheet.  And the rate of sea level is slowly increasing.....a few years ago sea level was only rising at 3 mm per year, and ten years before that at only 2.5 mm per per year, and 50 years ago sea level was only going up 1 mm per year.   

Some years ago I spent two months off the east coast of Greenland on the Glomar Explorer, the international scientific drilling vessel.  I was part of a science team that drilled a series of scientific cores into the sea floor along a line reaching out from Greenland and into the North Atlantic.  On the Continental Shelf all around Greenland we encountered glacial till and other glacial deposits, and in the deep sea beyond the edge of the continental shelf we drilled through sequences of sediments deposited by ice bergs calving off the Greenland ice Sheet.  The earliest record of ice bergs dated back to 7 million years ago, indicating the Greenland Ice Sheet had been present then.  This was a big discovery---our paper on this discovery appeared in Science because we had pushed back the age of the earliest glaciation of Greenland by several million years.  We did good.  But we missed a big part of the story.

Today I look at the record of glaciation on Greenland much differently.  Yes, the earliest record of glacial deposits goes back to 7 million years, but there were portions of the drill core above the lowermost glacial sediments where glacial sedimentation apparently stopped, and then resumed, and then stopped and resumed..  When we wrote our paper for Science we ignored these cycles and focussed on the maximum age of glaciation.  But today, based on how rapidly the Ice Sheet is melting now, most likely that the Greenland Ice Sheet disappeared during multiple warm intervals in the past.   Some past interglacial periods were warm enough to melt the ice sheet.  It then would reform during Ice Ages,and sometimes survive the next interglacial, and sometimes. not.  

The Greenland ice sheet was set to survive our current interglacial before homo sapiens came along.  But the Greenland Ice Sheet never previously encountered anything like 5 billion people trying to live the good life.  Sadly, once James Watt invented the coal-fired steam engine and Henry Ford invented the auto assembly line, the Greenland Ice Sheet never had a chance.