Climate change: Stark warning of 'irreversible changes' - BBC News
A major UN climate change report portrays an overheating world, urging governments to cut emissions.
We need to talk about that scary dotted line in the IPCC's sea-level projections - the one that says a global ocean rise approaching two metres by the end of the century can't be ruled out.

This outcome is considered a low probability but it would have major impact if it happened.

The line has been included because there are processes that can affect the melting and break-up of ice sheets which scientists still don’t yet fully understand. One of these is something called Marine Ice Cliff Instability, or MICI (pron: Mickey).

This is a scenario in which ice sheets could crumble away very quickly if the retreating edges of, say, Antarctica exposed extremely tall cliffs of ice. We know from the physics of ice that such structures cannot support their own weight and will slump.

The question is: how likely is MICI to take hold in Antarctica and how fast could it progress?

Right now, scientists can't answer this. They see some evidence for the process having occurred in the Earth's history; and think if it did happen, it's a possibility only under the most pessimistic warming futures.

Dr Rob Larter, a marine geophysicist with the British Antarctic Survey, commented: "With the present state of knowledge I agree with the description of runaway MICI as a low probability. However, I think it would be negligent to ignore it."

One final word. Don't lose sight of the sea-level rises that this report considers very likely. Remember, every additional centimetre increase in the height of the oceans puts more people at risk of coastal flooding.