What next?

Antarctic glaciers calving faster into the ocean

The edges of the Antarctic ice sheets are slipping into the ocean at an unprecedented rate, raising fears of a global surge in sea levels, glaciologists warned on Monday.

The findings confound predictions made just four years ago, by the UN’s Intergovernmental Panel on Climate Change (IPCC), that Antarctica would not contribute significantly to sea level rise in the 21st century.

In one area, around the Amundsen Sea in West Antarctica, glaciers are dumping more than 110 cubic kilometres of ice into the ocean each year, Eric Rignot of NASA’s Jet Propulsion Laboratory in California, US, told a meeting at the Royal Society in London, UK. This loss, which is increasing each year, is many times faster than the ice can be replaced by snowfall inland, he says.

The impending ice disaster centres on Pine Island Bay on the shores of the Amundsen Sea, where the Pine Island and Thwaites glaciers enter the sea. These glaciers, like many in West Antarctica, are perched on underwater mountains. The meeting heard that warmer ocean waters are circulating beneath the ice and melting their bases at a rate of 50 metres a year....

These glaciers are being dubbed the “plug hole” of the West Antarctic Ice Sheet. If the Pine Island and Thwaites glaciers disappeared, they alone could raise sea levels worldwide by more than a metre, says Rignot....

Researchers also warned that the larger East Antarctic Ice Sheet is not as stable as thought. A recent study suggested that it might be accumulating snow in its high interior – possibly supporting the IPCC’s predictions – but it warned that little was known about events on the coast (Science, vol 308, p 1898).

Last February I mentioned (in response to an ealier piece about the failing WAIS) that should the East Antarctive Ice Sheet start to collapse, we could see very rapid, very large increases in the sea level. If all of the EAIS collapsed we could conceivably see a 60 metre (180 feet) increase in sea levels. That's obviously the worst-case scenario, but the corollary to that fact is that even a much smaller rate of loss would lead to massive changes.

For a brief moment, it looked like global-warming induced sea level changes would in fact be quite minor, or at least something we could adjust to over the next century. The IPCC report mentioned above predicted something like a half-meter rise over 100 years. That's a lot, but it's liveable. In the last four years, we've got evidence that the two largest reserves of ice on the planet - Greenland and Antarctica - are becoming increasingly unstable. This is bad, bad news.