The good news is that it would take more than 1,000 years to melt the massive ice sheet in west Antarctica that could raise sea levels by 16 feet.
The bad news is this event could become unstoppable this century if carbon dioxide concentrations keep rising as predicted, a study has found.
An investigation into the stability of the ice sheet has found it has collapsed before when carbon dioxide concentrations in the atmosphere have reached about 400 parts per million, a level expected to reached by 2050.
It will almost certainly collapse when nearby ocean temperatures rise by about 5C, the likely result of global warming this century.
Two groups of researchers say the ice sheet has collapsed regularly, most recently about 400,000 years ago and one million years ago, resulting in large increases in sea levels. The two studies are published in the journal Nature.