The precariously moored West Antarctic ice sheet probably won't collapse into the ocean all in one go as the climate warms. But the bad news, says a researcher, is that the sections most likely to be released into the ocean would raise sea levels globally by 3.3 metres – and rather more on the shores of North America.
The West Antarctic ice sheet, the smaller of the icy continent's two giant slabs of ancient ice, is moored to an archipelago of islands, many of them below sea level. It is held in place by floating ice shelves. Glaciologists had feared that warm water could melt the shelves, releasing the entire sheet into the ocean, raising sea levels by up to 5 metres.
Concern has increased with recent failures of floating Antarctic ice, such as the Wilkins shelf. A recent study (pdf format) found that the West Antarctic ice sheet would probably collapse if sea temperatures rose by more than 5 °C.
But now Jonathan Bamber at Bristol University, UK, has analysed which parts of the West Antarctic ice sheet are vulnerable. He concludes that a third might stay put, mostly because it is moored above sea level. "The area's potential contribution to sea level has been greatly overestimated," he says.
Unfortunately, however, the loss of Antarctic ice would shift the Earth's gravitational pull, causing water to pile up in the northern hemisphere. Around North America this could increase anticipated sea-level rise by about a quarter.
In March, Bamber argued that the other giant ice sheet vulnerable to global warming, the Greenland ice sheet, is also more resistant to temperature rise that experts had thought.
But not all glaciologists think it has significantly changed the planet's immediate prognosis.
"The crucial question is how much ice could be lost in the next 100 to 200 years, and Jonathan's work has not really changed that," says David Vaughan of the British Antarctic Survey. Most predictions, he says, put global sea-level rise in the coming century at around 1 metre – but more will follow.
Journal reference: Science (DOI: 10.1126/science.1169335)
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