Antarctica had lost three trillion tonnes of ice in less than three decades

What happens in only the next decade could determine the fate of Antarctica - and the world. Photo / Regina Eisert

What happens in only the next decade could determine the fate of Antarctica - and the melting continent's future impact on our coastal cities and communities.

Scientists have sketched two 2070 scenarios - one leaving warming unchecked, another avoiding the worst effects of climate change - alongside new research that revealed Antarctica had lost three trillion tonnes of ice in less than three decades.

In the first scenario, the world's greenhouse gas emissions kept rising, with little policy action taken to slow climate change's impact on Antarctica.

That meant a dramatic loss of major ice shelves, sea warming, sea-ice retreat and ocean acidification and metres of global sea-level rise over coming centuries.

But under the low emissions scenario - which could be achieved if future temperature rise was limited to the 2C threshold sought by the Paris Agreement - Antarctica would look much as it did in the earlier decades of the century, and global sea-level rise would remain under the one-metre mark.

The new reasearch shows global sea levels are rising three times faster than a quarter of a century ago because of global warming.

Ice losses from Antarctica have increased sea levels by almost 8mm since 1992, with two-fifths of this rise coming in the past five years alone.

"The bad news is that time is short and emissions need to peak in the next decade and reduce to zero before the end of the century," said co-author Professor Tim Naish, of Victoria University's Antarctic Research Centre.

Naish said other risks - such as competition for resources and food security - could threaten the long-standing Antarctic Treaty, and New Zealand's own influence on the continent's preservation.

"Urgent action is needed," Naish said.

"Put simply, if we cannot collectively tackle climate change, then it's unlikely we will maintain Antarctica as a place for peace, nature and science."

A special edition of the major scientific journal Nature also included a raft of new research on the continent, which bore an equivalent 58m of potential sea-level rise.

Before 2012, Antarctica lost ice at a steady rate of 76 billion tonnes per year – a 0.2 mm per year contribution to sea level rise.

But since then there has been a sharp, threefold increase.

Between 2012 and 2017 the continent lost 219 billion tonnes of ice per year – a 0.6 mm per year sea-level contribution.

And between 1992 and 2017, the Antarctic Ice Sheet lost about three trillion tonnes of ice - equivalent to around 8mm of mean sea-level rise.

During this 26-year period, ocean-driven melting led to a tripling of ice-loss rates from West Antarctica, from 53 billion to 159 billion tonnes per year.

The rate of ice loss from the Antarctic Peninsula increased from about 7 billion to 33 billion tonnes per year as a result of ice-shelf collapse.

In West Antarctica, ice shelves were being eaten away by warm ocean water, and those in the Amundsen and Bellingshausen seas are up to 18 per cent thinner than in the early 1990s.

At the Antarctic Peninsula, where air temperatures had risen sharply, ice shelves have collapsed as their surfaces have melted.

Altogether, 34,000 sq km of ice shelf area had been lost since the 1950s.

While East Antarctica's mass balance remained highly uncertain and was indistinguishable from zero, reassessments of the models could improve understanding of what was happening.

"The new collection of research and review papers paint a clear and coherent picture about the things that keep Antarctic scientists up at night," said Professor Christina Hulbe, of the University of Otago.

While massive change was clearly underway in Antarctica and in the Southern Ocean, Hulbe said that didn't mean the new evidence should be read as doom and gloom.

"While some amount of change is already locked in, there are always choices to be made and it's still possible to avert the worst of the climate projections."