The vast ice sheets of the Antarctic may be more stable than we thought, because a key piece of physics has been overlooked.
Glaciologists have long worried that the West Antarctic ice sheet will collapse over the next few centuries, raising sea levels dramatically. At present the ice sheet is grounded on underwater islands, which insulate some of the ice from the melting effect of the seawater upon which the rest of the sheet floats. But because the ice has started to melt because of climate change, more water is probably flowing underneath the sheet over the surface of the islands, accelerating its destruction.
The ice sheet has a defence mechanism, however. As it melts, sea levels around it will fall, say Natalya Gomez and Jerry Mitrovica of Harvard University and colleagues. That is counterintuitive, because the ice sheet will release extra water into the sea – but because the mass of ice has shrunk, its gravitational pull on the seawater will be weaker. Also, the bedrock will rise up as the weight of ice on it drops.
“You get a fall in sea level within 2000 kilometres of the ice sheet,” Mitrovica says. This means there will be less water sloshing around the sheet’s base, so it will last longer. “It will slow down the retreat,” says Gomez.
The findings need to be included in the models used to predict ice sheet melting, says David Vaughan of the British Antarctic Survey in Cambridge, UK. But he says the gravitational effect would only make a big difference if the entire sheet were melting at once – which so far it isn’t.
Journal reference: Nature Geoscience, DOI: 10.1038/ngeo1012
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