When the Greenland Ice Sheet melts, and, according to this article, it’s beyond the point of no return, the oceans will rise approximately 20 feet. Now this may take thousands of years, but check out this excerpt:
Starting in 2000, Greenland’s glaciers suddenly began moving faster, their snouts rapidly retreating and thinning where they flow into the sea. Between 2000 and 2005, that acceleration led to an all-but irreversible “step-increase” of ice loss, scientists concluded in the new research, published this week in the journal Nature Communications Earth & Environment.
If the climate were to stop warming today, or even cool a little, Greenland’s ice will continue to melt, said Ohio State University Earth scientist Ian Howat, co-author of the research paper. “Glacier retreat has knocked the dynamics of the whole ice sheet into a constant state of loss,” he said.
Whether or not this event is inevitable, the imperative remains to slow it down as much as possible. This means the rapid migration to low-carbon energy sources, and a wholesale change in the way that humankind manages its land.