Race to save Antarctica's sleeping giant

The East Antarctic sheet, due south of Tasmania, has been dubbed a sleeping giant for good reason. If the entire area were to melt, global sea levels would rise 52 metres.

The sheet has long been considered less vulnerable to warming oceans because it sits on higher ground. As a result, it's been the subject of relatively little research.

But scientists who have just reviewed everything known so far about the behemoth now say it's not as stable and protected as once thought.

It turns out some parts of the bedrock beneath the ice sheet are very deep and sit well below sea level. Part of the Denman glacier, for example, sits on ground that's 3.5 kilometres below sea level.

Experts know that's a problem because the same features have caused big problems for the much smaller, adjoining West Antarctic ice sheet.

"That's why the West Antarctic ice sheet is so vulnerable and is already changing quickly and contributing to sea level rise," says Australian National University Professor Nerilie Abram, who worked on the new review.

"In these deep basins, the ground is below sea level and that means the front of the ice sheet is in contact with the ocean.

"As the ice sheet starts to melt and retreat, it sets up a situation where more and more of the front of the ice sheet is in contact with those ocean waters, so the ocean becomes even more effective destabilising that section of the ice."

"We know there are some of these areas around the East Antarctic so they have that same set-up to potentially become destabilised."

The review also looked at how much sea levels could rise if climate change melts the eastern sheet.

If global warming is kept to well below 2C - the primary objective of the Paris climate pact - the sheet will add less than half a metre to sea-level rise by 2500.

But failure could add five metres.

Professor Abram says the window of opportunity to shield the ice sheet from climate change is rapidly closing.

"Even though we are talking about sea level rises that are going to happen over centuries to come it's the decisions we're going to make this decade that are going to tell us what pathway we are on," she says.

"Are we going to end up in a situation where we destabilise parts of the East Antarctic ice sheet so we then have areas that no matter what we do, we're going to lose ice?

"Or can we be on that much more optimistic pathway, make the emissions reductions and limit warming to well below 2C. Then we actually have a very good news story, that we can can keep most of the ice sheet very quiet."

The review was led by Durham University in the United Kingdom in collaboration with scientists from Australia, France, the US and the UK. It has been published in the journal Nature.

Australian Associated Press