Climate change: Sea level rise could displace millions of people within two generations | Jonathan Bamber & Michael Oppenheimer

Antarctica is further from civilization than any other place on Earth. The Greenland ice sheet is closer to home but around one-tenth the size of its southern sibling. Together, these two ice masses hold enough frozen water to raise global mean sea level by 65 meters if they were to suddenly melt. But how likely is this to happen?
The Antarctic ice sheet is around one and half times larger than Australia. What’s happening in one part of Antarctica may not be the same as what’s happening in another – just like the east and west coasts of the US can experience very different responses to, for example, a change in the El Niño weather pattern. These are periodic climate events that result in wetter conditions across the southern US, warmer conditions in the north and drier weather on the north-eastern seaboard.

The stabilizing effect of bedrock rising as the overlying ice thins, lessening the weight on the bed, is an example of negative feedback, as it slows the rate that the ice melts.

The ice in Antarctica is nearly 5km thick in places and we have very little idea what the conditions are like at the base, even though those conditions play a key role in determining the speed with which the ice can respond to climate change, including how fast it can flow toward and into the ocean. A warm, wet base lubricates the bedrock of land beneath the ice and allows it to slide over it.
These issues have made it particularly difficult to produce model simulations of how ice sheets will respond to climate change in future. Models have to capture all the processes and uncertainties that we know about and those that we don’t – the “known unknowns” and the “unknown unknowns” as Donald Rumsfeld once put it. As a result, several recent studies suggest that previous Intergovernmental Panel on Climate Change reports may have underestimated how much melting ice sheets will contribute to sea level in future.

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