Anarctic ice sheet melting faster than expected

[Chris]

The world's largest ice sheet has started to melt along its coastal fringes, raising fears that global sea levels will rise faster than scientists expected.

The East Antarctic ice sheet, which makes up three-quarters of the continent's 14,000 sq km, is losing around 57bn tonnes of ice a year into surrounding waters, according to a satellite survey of the region.

Scientists had thought the ice sheet was reasonably stable, but measurements taken from Nasa's gravity recovery and climate experiment (Grace) show that it started to lose ice steadily from 2006.

The measurements suggest the polar continent could soon contribute more to global sea level rises than Greenland, which is shedding more than 250bn tonnes of ice a year, adding 0.7mm to annual sea level rises.

Satellite data from the whole of Antarctica show the region is now losing around 190bn tonnes of ice a year. Uncertainties in the measurements mean the true ice loss could be between 113bn and 267bn tonnes.

"If the current trend continues or gets worse, Antarctica could become the largest contributor to sea level rises in the world. It could start to lose more ice than Greenland within a few years," said Jianli Chen, of the University of Texas at Austin.

World's largest ice sheet melting faster than expected | Environment | guardian.co.uk

 

[waltky]

Higher than previous predictions...

'Best estimate' for impact of melting ice on sea level rise
14 May 2013 - Researchers have published their most advanced calculation for the likely impact of melting ice on global sea levels.

The EU funded team say the ice sheets and glaciers could add 36.8 centimetres to the oceans by 2100. Adding in other factors, sea levels could rise by up to 69 centimetres, higher than previous predictions. The researchers say there is a very small chance that the seas around Britain could rise by a metre. The last Intergovernmental Panel on Climate Change (IPCC) report was highly detailed about many aspects of Earth's changing climate in the coming decades.

Advanced models

While they estimated that sea levels could rise by 18-59 centimetres by 2100, they were very unsure about the role played by the melting of ice sheets and mountain glaciers. To fill the void, the EU funded experts from 24 institutions in Europe and beyond to try and come up with more accurate figures on the melting of ice sheets and glaciers in Antarctica and Greenland and how this might swell the oceans. Called Ice2sea, the group of scientists have made what they term the "best estimate" yet of the impact of melting based on a mid-range level of carbon emissions that would increase global temperatures by 3.5C by the end of this century. "For that one scenario we have an ice sheet and glaciers contribution to sea level rise of between 3.5 and 36.8 cm by 2100," said Prof David Vaughan from the British Antarctic Survey who is the co-ordinator of the Ice2sea programme.

Researchers say they now have the most accurate estimate yet for the impact of the melting of ice sheets

While the range is wide, the scientists say it is a relatively robust calculation and based on several advances in their modelling since the last IPCC report. "In order to be able to model the ice sheet properly you need to be able to resolve things down to hundreds of metres," says Prof Tony Payne from the University of Bristol. "That's quite a task when an ice sheet is a thousand kilometres or more in size, that's a very demanding computational task. What we found is that the Pine Island glacier, the poster child of sea level rise in the Antarctic, that will continue through to the end of the century and very little else happens."

Despite the improvements, there are still many factors that are difficult to include in models. To get around this, the leading researchers were asked to estimate the worst-case scenarios. They concluded there was a one in 20 chance that the melting ice would drive up sea levels by more than 84 centimetres, essentially saying there's a 95% chance it wouldn't go above this figure. While ice melt is a major contributor to the height of the seas, there are other important factors especially thermal expansion caused by the warming of the waters. This is estimated to be raising sea levels by 3 millimetres every year. Taken together with the ice melt estimate, the scientists say the overall, maximum impact on the seas by 2100 will be a rise of 69 centimetres - just ten centimetres higher than the IPCC projection in 2007, termed AR4.

More BBC News - 'Best estimate' for impact of melting ice on sea level rise