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Antarctic glaciers emptying into the Bellinghausen Sea all suddenly started melting around 2009. Scientists warn the sea level rise could be dramatic.

THE FIRST SIGNS Antarctic glaciers have reached some kind of melting 'tipping point' have been noticed by scientists from Europe. The group of eight scientists, led by Dr Bert Wouters from the University of Bristol used sophisticated satellite measurements of the Antarctic glaciers that empty into the Bellinghausen Sea, on the Southern Antarctic Peninsula which reaches up almost to South America. Glaciers are in effect, frozen rivers of snowpack, moving incrementally towards the ocean. These glaciers have existed in their current form for at least 5,000 years. The scientists found that the height of the glaciers had dropped — some by as much as four metres. By analysing years of data, they could rule out the snow becoming more compact or a reduction in snowfall as the cause. This left only one possibility: that the glaciers were sliding faster towards the sea. "The most likely explanation is that the glaciers have accelerated because the temperature of the ocean water has increased in the area, which we know from measurements. These warm waters will melt the floating ice shelves and the glaciers where they enter the sea from below and cause them to lose more ice," said Dr Wouters, Marie Curie Research Fellow at the University of Bristol. As the sea ice holding back the glaciers melts away, the glaciers slide faster into the sea. Last week researchers warned that elsewhere in Antarctica, the Larsen C ice shelf could collapse this century and what remains of the Larsen B ice shelf would be all gone by 2020, the majority of it having collapsed in 2002.

A tipping point

Curiously, the glaciers studied were relatively stable until 2009. After then, Dr Wouters said the glaciers appeared to have reached a "tipping point" with the glaciers studied simultaneously starting to slip into the sea. "We don't know exactly [what happened]. We do know that the water has been warming since at least the 1980s and that as a result, the ice shelves floating in front of the glaciers have been thinning since at least the 1990s," said Dr Wouters. "For many things in the climate system, a critical point needs to passed before big changes occur, and it seems that around 2009 such a point was passed for the glaciers on the coast of the Bellingshausen Sea." Dr Wouters said the slipping glaciers are of concern because of the potential contribution they could make to sea level rise. "In the area we studied, there's enough ice to raise sea level by 35 cm," he said. And while the glaciers won't completely melt in the near future, they could still make a significant contribution to global sea level rise. Since 2010 the glacier melt in just the area studied has added roughly 55 trillion litres of water to the ocean, accounting for 0.16mm of global sea level rise each year. Although climate change certainly plays a part in the warmer Antarctic waters, other factors are at play as well. "The increase in water temperature is a result of changing wind patterns around Antarctica. There's a band of westerly winds blowing around Antarctica and these winds have increased in strength the past decades. The reasons for this are not 100 per cent understood, but most studies indicate that this is a result of global warming and the ozone hole above Antarctica." Dr Wouters warns that if these glaciers can start slipping away so rapidly, there is every chance other glaciers could behave in the same way. "Our study shows that the ice sheet responds very rapidly to changes in its environment and that rapid ice loss can start within a couple of years, without any 'warning' signs beforehand. This could also happen in other regions which are now quiet, if the conditions are right."

The study is published today in the journal Science.

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