Ice sheets may stabilise for centuries, regardless of warming
The tap filling up the oceans sometimes just turns off
Ice sheets retreating due to global warming often suddenly stabilise for "decades to centuries" no matter that the warming is still going on, scientists have found. The new research would seem likely to have an impact on forecasts seeking to predict sea-level rise in coming times.
Boffins at Cambridge, Durham and Sheffield universities and others at the British Antarctic Survey came together to produce the new investigation, which sought to examine the way in which fast-moving "ice streams" move from major ice sheets - such as the Greenland and Western Antarctic ones - to the sea. The streams are very important, as they carry 90 per cent of the ice moving into the ocean.
“Ice streams are like taps filling a bath," explains Dr Chris Stokes of Durham uni - in this case the bath being the world's oceans.
"The problem here is that we do not know if something is suddenly going to turn them up or even turn them off," he adds.
In this case Stokes and his colleagues didn't find anything which would open up the taps: but they did find something which turns them off, often for lengthy periods.
"Our research shows that the physical shape of the channels is a more important factor in controlling ice stability than was previously realised," says Dr Stewart Jamieson.
The boffins found this out by developing a simulation which matched what actually happened to a particular ice sheet as it retreated at the end of the last Ice Age:
The researchers looked at the landscape of the seafloor in Marguerite Bay, in the Antarctic Peninsula, and saw that during a rapid phase of recession 13,000 years ago, retreat paused many times. Using a computer model designed to work in situations of rapid change, they found they could reproduce the same pattern in a series of simulations. These showed that ice dragged on the sides of the channel more where it was narrow, causing retreat to slow and in places temporarily stop for decades to centuries before retreat continued.
"We find that retreat of the Marguerite Bay Ice Stream following the [Last Glacial Maximum] was highly nonlinear and was interrupted by stabilizations on a reverse-sloping bed, where theory predicts rapid unstable retreat," the researchers wrote in their new paper, published in Nature Geoscience.
It would seem that current predictions of sea level rises to be expected on a given timescale with a given amount of global warming will need to be revised - downwards.
As the most up-to-date predictions are not very alarming anyway, it could be that sea level rises just aren't that big a worry, over say the next century anyway. ®