Ancient Antarctic ice melt increased sea levels by 3+ metres – and it could happen again

“We now have some of the first major evidence that West Antarctica melted, and drove a large part of that ancient sea level rise,” said lead researcher Professor Chris Turney from the University of New South Wales.

“This study also shows that we would lose most of the West Antarctic Ice Sheet in a warmer world,” he said.

The research was undertaken at the Patriot Hills Blue Ice Area, on the edge of the West Antarctic Ice Sheet.

“Whereas most Antarctic researchers drill down into the ice to collect their samples, in blue ice areas fierce winds erode the surface layers, causing ancient ice to flow to the surface, carrying with it evidence of earlier climates,” James Cook University’s Professor Michael Bird said.

Professor Bird and JCU colleague Dr Niels Munksgaard conducted the isotopic analysis of the ice.

“Our job was to look at the chemical signatures in the ice to help identify changes in air temperature and source of the water, and compare those with times before and after the Last Interglacial,” said Professor Bird, a chief investigator at the ARC Centre of Excellence for Australian Biodiversity and Heritage (CABAH).

“Along with other analyses, including measures of volcanic ash and DNA from bacteria trapped in the ice, the team was able to confirm the timing. The evidence all points to rapid ice loss from the West Antarctic Ice Sheet coinciding with the extreme sea level increase of the Last Interglacial.”

Professor Bird said the findings helped to fill a gap in understanding of the Last Interglacial, when global warming triggered by changes in Earth’s orbit led to sea levels between six and nine metres higher than present day.

“That degree of sea-level rise couldn’t be fully accounted for by the melting of the Greenland Ice Sheet, and ocean expansion from warmer temperatures and melting mountain glaciers,” he said. “Evidence of significant Antarctic ice loss at that time helps us better understand the Last Interglacial, which in turn gives us a clearer view of what the future might hold.”

Using data gained from their fieldwork, the team also ran model simulations, with results suggesting a 3.8 metre sea level rise during the first thousand years of a 2˚C warmer ocean.

At present, the consensus of the Intergovernmental Panel on Climate Change (IPCC) 2013 report suggests that global sea level will rise between 40cm and 80cm over the next century, with Antarctica contributing only around 5cm of this.

The researchers are concerned that Antarctica’s contribution could be much greater than this.

“Recent projections suggest that the Antarctic contribution may be up to ten times higher than the IPCC forecast, which is deeply worrying,” said Professor Christopher Fogwill, co-author and Director of The Institute for Sustainable Futures at the UK University of Keele.

“Our study highlights that the Antarctic Ice Sheet may lie close to a tipping point, which once passed may commit us to rapid sea level rise for millennia to come. This underlines the urgent need to reduce and control greenhouse gas emissions that are driving warming today.”

Notably, the researchers warn that this tipping point may be closer than we think.

“The Paris Climate Agreement commits to restricting global warming to 2˚C, ideally 1.5˚C, this century,” said Professor Turney, a Chief Investigator and leader of the Climate theme at CABAH.

“Our findings show that we don’t want to get close to 2˚C warming.”

The research is published today in Proceedings of the National Academy of Sciences.