Can the world stop polar ice sheets collapsing?

The world's ice sheets could still collapse with less than 2C of warming, a new review has found. Photo / File

The world's goal to limit global warming to no more than 2C may not be enough to stop the collapse of polar ice sheets, scientists say.

An international scientific review co-authored by Victoria University researcher Associate Professor Nick Golledge found ice sheets in Antarctica and Greenland had tipping points at which melting would rapidly ramp up, and ice sheet retreat could become unstoppable.

Golledge's colleague, Associate Professor Rob McKay, said the reason for this differed between hemispheres, with melting of Greenland controlled by atmospheric warming and Antarctica by oceanic warming.

But the threshold to reach these tipping points in both regions was between 1.5 to 2C, which suggested that even if the obligations of the Paris Agreement were met, the world would come "extremely close" to the point of no return for accelerated retreat, McKay said.

"While this melting will play out over hundreds to thousands of years, it is apparent from this work that the more we overshoot the 1.5C target, the more rapid this accelerated ice sheet melt will be."

Professor Tim Naish, also of Victoria University's Antarctic Research Centre, said the new review was timely, given the recent release of a UN special report focused on limiting warming to 1.5C.

"Without some degree of direct carbon extraction from the atmosphere, we are unlikely to avoid it," Naish said.

"This review summarises the progress made since the IPCC's 5th Assessment Report in 2013 on understanding the poorly known, but potentially very significant, dynamic contribution of the polar ice sheets to future sea-level rise."

Naish noted how a study by Golledge in 2015 was one of the first to suggest there may be a threshold in the Antarctic ice sheet somewhere close to the Paris Agreement target of 2C.

"Above this level of warming, parts of the ice sheets could be committed to irreversible loss over coming centuries to millennia."

Professor Christina Hulbe, of Otago University's School of Surveying, said better models were an opportunity to assess how different parts of the coastline would be affected by sea level rise.

"The new report makes another point that is sometimes lost in the conversation: even if we meet the Paris targets and keep the warming in check, we're still committed to continued ice loss over the 21st century, and with it continued sea level rise," she said.

"I would add to this caution that some of the tipping processes may have already been invoked, at least in some parts of Antarctica but understanding that in detail requires more work."