Largest ice shelf in Antarctica could break up: study

The largest ice shelf in the Antarctic is being thinned by global warming and could catastrophically break up, contributing significantly to sea level rise, scientists warned today.
The Larsen C Ice Shelf - whose neighbours Larsen A and B, collapsed in 1995 and 2002 - is thinning from both its surface and beneath, researchers said.
For years scientists have been unable to determine whether it is warming air temperatures or warmer ocean currents that were causing the Antarctic Peninsula's floating ice shelves to lose volume and become more vulnerable to collapse.
The new study carried out by scientists from British Antarctic Survey, the US Geological Survey, University of Colorado, University of Kansas and Scripps Institution of Oceanography takes an important step forward in assessing Antarctica's likely contribution to future sea-level rise.

The team combined satellite data and eight radar surveys captured during a 15-year period from 1998-2012. They found that Larsen C Ice Shelf lost an average of 4 metres of ice, and had lowered by an average of one metre at the surface.
"What's exciting about this study is we now know that two different processes are causing Larsen C to thin and become less stable," lead author, Dr Paul Holland from British Antarctic Survey (BAS), said.

"Air is being lost from the top layer of snow (called the firn), which is becoming more compacted - probably because of increased melting by a warmer atmosphere. We know also that Larsen C is losing ice, probably from warmer ocean currents or changing ice flow," Holland said.

"If this vast ice shelf - which is over two and a half times the size of Wales and 10 times bigger than Larsen B - was to collapse, it would allow the tributary glaciers behind it to flow faster into the sea. This would then contribute to sea-level rise," said Holland.
The Antarctic Peninsula is one of the fastest warming regions on Earth, with a temperature rise of 2.5 degrees Celsius over the last 50 years, researchers said.
The team, who continue to monitor the ice shelf closely, predicts that a collapse could occur within a century, although maybe sooner and with little warning.

A crack is forming in the ice which could cause it to retreat back further than previously observed. The ice shelf appears also to be detaching from a small island called Bawden Ice Rise at its northern edge.
"When Larsen A and B were lost, the glaciers behind them accelerated and they are now contributing a significant fraction of the sea-level rise from the whole of Antarctica," Professor David Vaughan, glaciologist and Director of Science at BAS, said.
"Larsen C is bigger and if it were to be lost in the next few decades then it would actually add to the projections of sea-level rise by 2100," Vaughan added.

The study was published in journal The Cryosphere.