Greenland‘s ice caps are apparently melting at a rapid clip. Here is a story that discusses the potential problems of this happening. In addition there is discussion about how current climate models may not be able to predict how high sea levels can go. The article says that sea levels can increase by 25 meters! Excerpt:

Our Nasa scientists have measured this in Greenland. And once these ice streams start moving, their influence stretches right to the interior of the ice sheet. Building an ice sheet takes a long time, because it is limited by snowfall. But destroying it can be explosively rapid.

How far can it go? The last time the world was three degrees warmer than today – which is what we expect later this century – sea levels were 25m higher. So that is what we can look forward to if we don’t act soon. None of the current climate and ice models predict this. But I prefer the evidence from the Earth’s history and my own eyes. I think sea-level rise is going to be the big issue soon, more even than warming itself.