Another under-reckoning.
From Nature:

Recent studies have focused on the short-term contribution of the Greenland ice sheet to sea-level rise, yet little is known about its long-term stability.
…
Here, using a fully coupled model, we show that this criterion systematically overestimates the temperature threshold and that the Greenland ice sheet is more sensitive to long-term climate change than previously thought.

And the backlash commonly cited by this process is the rise of sea levels — the rub, though, is that nasty-ass methane bubbling up into the environment with the melting.