A lot of the climate models seem to have modelled the ice sheets as ice cubes when they behave more like a drop of honey.

Lately I have been reading articles in Science News and elsewhere about glacial lakes melting holes through very thick glaciers and disappearing through said holes. It appears that this additional water further lubricates the interface between the ice and the rock below, increasing the rate of glacier flow. Such processes have been observed both in Greenland and West Antarctica.  I believe that the melting of the two ice sheets would product an increase of about 70 meters in sea level.

I recall an article arguing that the break-up of the North American Ice Sheet at the end of the last ice age had occured quite rapidly and that the influx of fresh water had temporarily disrupted the Gulf Stream and that this accounted for an unexplained episode of re-glaciation in Western Europe.  Non-linear processes can proceed quite rapidly.  This is what makes me worry that it may be later than we think.

"It is not necessary to have hope in order to persevere."