Parts of the West Antarctic ice sheet are already collapsing and probably can鈥檛 be saved. Two independent studies suggest that several glaciers have gone past the point of no return, dooming them to fall into the sea and cause several metres of sea level rise. However the collapse will take centuries.
鈥淎 large sector of the West Antarctic ice sheet has gone into irreversible retreat,鈥� says of the University of California at Irvine, who led one of the studies. 鈥淲e鈥檝e gone beyond the point of no return.鈥�
A study led by of the University of Washington in Seattle focuses on the Thwaites glacier, a key component of the West Antarctic ice sheet (WAIS). It predicts that the glacier will collapse completely within 200 to 1000 years, raising global sea levels by about 60 centimetres.
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But because the Thwaites glacier keeps much of the rest of the WAIS in check, its disappearance could destabilise the entire sheet, releasing enough ice to raise sea levels by a further 3 to 4 metres.
Shrinking ice
Joughin and his colleagues used radar images from the air to accurately map the rocks beneath the Thwaites glacier. This enabled them to map the receding 鈥済rounding line鈥�, the point at which a glacier rests on open water rather than on rock. The deeper the grounding line penetrates inland, the more ice is supported by water alone, and the likelier it is to collapse and melt.
Using this information, they modelled the glacier鈥檚 likely fate over the coming centuries, and projected that a rapid collapse will begin between 200 and 900 years in the future. Once under way, the collapse would cause sea levels to rise by at least 10 centimetres per century.
鈥淭he bad news is that such a collapse may be inevitable,鈥� says Joughin. The only uncertainty is over how fast the collapse will happen.
All in retreat
The other study, led by Rignot, tracked the retreats between 1992 and 2011 of the Thwaites glacier, the Pine Island Glacier and the Smith-Kohler glacier system. The results of both studies tally.
Rignot and his colleagues used radar interferometry measurements from satellites to track the retreats of the grounding lines of the glaciers.
Measured at their centres, the Thwaites glacier had retreated 14 kilometres, the Pine Island glacier by 31 kilometres, and the Smith-Kohler glacier system by 35 kilometres.
鈥淭he grounding line has been retreating at record speeds unseen anywhere else in the Antarctic,鈥� says Rignot.
No stopping it
Both studies found that there are no obstacles further inland, such as rocky outcrops, that could halt the retreats. 鈥淭here鈥檚 no barrier to stop it,鈥� says Rignot.
For that reason, Joughin says the Thwaites glacier is probably doomed. 鈥淚t looks like all the feedbacks tend to point towards it actually accelerating over time, as there鈥檚 no stabilising mechanism we can see,鈥� he says.
According to Rignot, the same is true for all the glaciers in the area, except the relatively small Haynes glacier. 鈥淓ven if the ocean was not warming up, it鈥檚 now a chain reaction that鈥檚 unstoppable,鈥� he says.
鈥淭he only thing that would stop it is a mountain where glaciers would have to climb uphill,鈥� adds Rignot. 鈥淲e are fairly confident there鈥檚 no such hill or mountain.鈥�
Journal references: Joughin et al: ; Rignot et al:
