Nick Tsagaris - The Rate Of Antarctic Melting Has Nearly Tripled In The Past Five Years

The Antarctic ice sheet has lost more than 2,500 billion tonnes of ice in the past 25 years and nearly half of that has happened since 2012.

An international team of polar scientists found that melting in Antarctica has jumped sharply from an average of 76 billion tonnes per year prior to 2012, to around 219 billion tonnes each year between 2012 and 2017.

That's adding 0.6 of a millimetre to sea levels each year. Antarctica stores enough water to raise global sea levels by 58 metres, and has contributed 7.6 millimetres since 1992, according to the research published in Nature today.

The latest data is a continuation of previous assessments known as the Ice sheet Mass Balance Inter-comparison Exercise (IMBIE), which began in 2011 and tracks ice-sheet loss from 1992 onwards.

IMBIE was established with the support of NASA and the European Space Agency, to monitor the changes in ice-sheet cover around the world.

It uses combined satellite data to measure the Antarctic ice sheet's changing flow and volume.

The increase in melting should act as a wake-up call, according to project leader Professor Andrew Shepherd from the University of Leeds.

"The rapid increase in Antarctic ice loss is due to ocean melting of glaciers in the Amundsen Sea, and ice shelf collapse on the Antarctic Peninsula," he said in a statement.

"These events and the sea-level rise they've triggered are an indicator of climate change and should be of concern for the governments we trust to protect our coastal cities and communities."

Emerging Antarctic sea-level rise research points to 'worst case scenarios'

West Antarctica contributed the most ice loss from the continent, shedding nearly 160 billion tonnes each year since 2012.

Although the general trend was of reduction, there was some increase in ice cover in East Antarctica.

This region has grown by an average of around 5 billion tonnes per year over the 25-year period, although margins of error could put that figure into the negative.

The researchers attribute the increased losses in West Antarctica and the Antarctic Peninsula to changes in regional floating-ice shelves, which can provide a buffer to continental-ice sheets.

In a separate analysis piece in Nature today, climate scientist and Antarctic policy expert Professor Rob DeConto warned that Antarctica may contribute more to sea-level rise than previously thought.

"Emerging science is pointing to more extreme worst-case scenarios with regards to sea-level rise from Antarctica," he stated.

"But the good news is that a reduction in emissions in line with the aspirations of the Paris Climate Agreement dramatically reduces the risk of flooding our coastlines in future decades and centuries."

But there is also room for caution in how this latest data is interpreted.

It's too early to say whether this melting trend will continue or slow down, according to CSIRO physical oceanographer Dr Steve Rintoul, who wasn't involved in the study.

"It's a difficult one for us to answer because the time series is still pretty short," he said.

"There's still a wide range in projections between what is going to happen in Antarctica in the future."

However, he said that there is growing evidence that projections of Antarctica's influence on sea-level rise may have been underestimated.

"What we have seen as the climate has warmed is that more warm water is reaching the Antarctic ice sheet and that's what is melting the sea ice," he said.

Separate research points to devastating role of ocean swell

As sea-ice retreats, floating Antarctic ice shelves are more exposed to destruction by wave action, according to a separate paper also published in Nature today and not affiliated with the previous study.

However, the role of sea ice in buffering ice shelves and continental ice sheets is rarely factored into Antarctic ice-loss modelling, according to lead researcher Dr Rob Massom from the Australian Antarctic Institute.

His team analysed the Larsen A and Larsen B, and Wilkins ice-shelf disintegration events, and found that lack of sea-ice was a common factor.

"It just so happens that offshore from those ice shelves, it's a hotspot of sea-ice loss," Dr Massom said.

"Ice shelves play a significant role in buttressing the discharge of grounded ice from the ice sheet into the ocean, and it's that ice that contributes to sea-level rise."

He argued that sea-ice loss needs to be considered in future modelling in order to more accurately forecast the contribution of the Antarctic ice sheet to sea-level rise in coming decades.

"The disintegration was an eye-opening thing. The glaciers that were feeding into those ice shelves accelerated by up to eight-fold [after the disintegration] and that happened pretty immediately," he said.

"This is a concerning thing if you consider that ice shelves exist around 75 per cent of the periphery of Antarctica. If this kind of thing happens more in the future we have to be aware of that."

By: abc.net.au