http://www.abc.net.au/news/2016-05-19/warning-on-tipping-point-for-east-antarctic-glacier/7425362

 

The Totten Glacier in East Antarctica has an unstable area that could collapse and contribute to more than two metres of sea level rise beyond what is generally predicted if climate change remains unchecked, researchers say.

 

East Antarctica is the world's largest area of ice and, until recently, was thought to be more stable than the smaller West Antarctic ice sheet.

The Totten Glacier, in particular, has rapidly become recognised as the most vulnerable of all the East Antarctic glaciers, with its floating ice shelf already in retreat.

"While traditional models haven't suggested this glacier can collapse, more recent models have," said Dr Alan Aitken of the University of Western Australia, co-author of a new study published today in the journal Nature.

Dr Aitken and colleagues have carried out the first study to analyse the stability of the Totten Glacier's ice sheet.

"We confirm that collapse has happened in the past, and is likely to happen again if we pass a tipping point, which would occur if we had between 3 and 6 degrees of warming above present."

Mapping reveals glacier's points of instability

The researchers studied patterns of erosion left by past ice sheet activity by mapping the topography of the land under the ice, and the thickness of its sedimentary rocks, which get eroded with glacial activity.

Beyond the ice shelf, they identified a relatively stable 100-kilometre-wide area, which slopes downwards towards the sea, allowing melting ice to be removed to the sea.

Ice sheets, glaciers, ice shelves and sea level rise

• As snow falls on the Antarctic continent it is slowly compacted over many years into vast ice sheets bigger than 50,000 square kilometres in size
• Glaciers are formed when this ice moves under gravity towards the coast
• As these glaciers flow into the sea they create permanent floating ice shelves connected to the land
• Because ice shelves are already floating in the ocean they don't contribute to sea level rise when they break up
• But, if an ice shelf collapses, the glaciers and ice sheet on land that feed it flow more quickly out to sea and do cause the sea level to rise

Beyond this was a 200-kilometre-wide unstable area that sloped down away from the sea. This would allow melted ice to pool at the bottom of the ice sheet and encourage its rapid melting.

The researchers said the first 100 kilometres of the ice sheet could melt within the next century, or it may take centuries or even millennia. But it if it all melted, it would add about 90 centimetres to sea level rise.

Then the main problem would be that it would expose the unstable section of the ice sheet to warm sea water and this section could collapse relatively rapidly in a matter of decades, adding an extra 1.5 metres, Dr Aitken said.

"We would reach a tipping point." he said.

He said the good news is that this scenario could be avoided if we limit global warming to 2 degrees above present levels.

"We have in this system at least a little bit of breathing space to cope with some temperature increase because of that stable zone," he said.

"But if we exceed that point, then we're looking at a large additional contribution that could have been avoided if we stuck to our target."