A recent feature in EOS by people at William's erstwhile institution and at my own adresses the lack of a clear constraint on the rate at which the West Antarctic Ice Sheet will fail, focusing on evidence that the mass may well leak out of an obscure and hitherto little-explored region called the Amundsen Embayment.
Want to know where that is? This map will draw your eye right to it. It's the place where the Antarctic surface elevation is dropping fastest. The current rates are not especially alarming. It's the lack of any obvious mechanism to constrain that rate from increasing by a couple of orders of magnitude that's the issue.
The base of this ice sheet is below sea level. That means the mechanics of its retreat is very different from the mechanics of retreat of land ice sheets. It is informed consensus that the very rapid sea level rise episodes of the not-too-distant past resulted from unstable decay of similar structures. A mechanism for abrupt retreat has been proposed.
Let me try to be clear. This is not to say that a couple of meters of sea level rise is imminent. It is to say that it might be relatively sudden when it happens, and that it might be imminent.
It's worth investigating and its worth modeling. I don't want to mess around in the politics of the situation too much, but it reinforces my distress about how science is funded to note that while the right people (I'm not speaking of myself, by the way; I would be pleased and lucky to be peripherally involved; I like being around people who are smarter than I am) are willing to do the work, there seems to be some difficulty identifying the "right pot of money".