Warming of 3°C could cause major jump in Antarctic ice melt

The paper, published today in Nature, uses computer model simulations to test the impact of several warming scenarios, including the Paris Agreement targets.

If the 1.5 or 2°C Paris Agreement temperature targets are achieved, the Antarctic Ice Sheet would contribute between 6 and 11 centimetres of sea-level rise by 2100.

But if the current course towards 3°C is maintained, the model points to a drastic acceleration in the pace of sea-level rise, with a tipping point reached around 2060.

Unless ambitious action to rein in warming begins well before 2060, no human intervention, including removing carbon dioxide from the atmosphere, would be able to stop 17 to 21 centimetres of sea-level rise from Antarctic ice melt alone by 2100.

The study involved University of Exeter researcher Dr Edward Gasson and was led by Professor Rob DeConto of the University of Massachusetts, Amherst.

“The Paris Agreement is a good start, however this study highlights the importance of more ambitious greenhouse gas emissions reductions ahead of the critical COP26 climate summit in Glasgow later this year,” Dr Gasson said.

The implications of exceeding Paris Agreement warming targets become even starker on longer timescales.

Antarctica contributes about one metre of sea-level rise by 2300 if warming is limited to 2°C or less, but reaches globally catastrophic levels of 10 metres or more under a more extreme warming scenario with no mitigation of greenhouse gas emissions.
This new research is informed by what happened to the Antarctic Ice Sheet in the geological past.
The model was tested against how well it simulates past changes in the Antarctic Ice Sheet before being used to simulate what might happen in the future.
The very architecture of the Antarctic Ice Sheet itself plays a key role in ice loss.
Ice flows slowly downhill, and the Antarctic Ice Sheet naturally creeps into the ocean, where it begins to melt.
What keeps that ocean-bound ice flowing slowly is a ring of buttressing ice shelves, which float in the ocean but hold back the upstream glacial ice by scraping on shallow sea-floor features.
Those buttressing ice shelves act both as dams that keep the sheet from sliding rapidly into the ocean, and as supports that keep the edges of the ice sheet from collapsing.

As warming increases, the ice shelves thin and become more fragile.
Meltwater on their surfaces can deepen crevasses and cause them to disintegrate entirely – this causes the tipping point in the model.

This not only lets the ice sheet flow toward the warming ocean more quickly, it leaves the exposed edges of the ice sheet vulnerable to breaking off or “calving” into the ocean, adding to sea level rise.

Dr Gasson, a lecturer in Environmental Science at Exeter, is funded by the Royal Society as a University Research Fellow.

The paper is entitled: “The Paris Climate Agreement and future sea-level rise from Antarctica.”