Successful Paris Agreement could halve ice loss by 2100

Limiting global warming to 1.5°C could halve the amount of Antarctic land ice lost by the end of the century, but maintaining current emissions – projected to raise global temperatures by 3°C by 2100 – will accelerate ice sheet loss and sea level rise past a point-of-no-return by 2060, according to two papers published today in Nature.

The Paris Agreement is an international accord among 197 nations to limit global warming this century to 2°C, while a more ambitious target of 1.5°C is seen as the preferred – but perhaps less realistic – result.

Falling short of both of these targets, current fossil fuel emissions have put the planet on track for 3°C of warming this century, substantially increasing the rate of ice loss over time.

This animation shows the rate at which the ice thickness is changing in metres per year (more red/yellow means faster thinning and thus faster ice loss) as the Antarctic Ice Sheet responds to changes in the atmosphere and ocean due to one potential climate scenario. This simulation, using the BISICLES ice sheet model, represents one of hundreds of such simulations used for this work to characterize ice sheet response to changes in the climate.
Credit: Daniel Martin and Courtney Shafer

The new projections are presented in two separate papers. In the first, Tamsin Edwards of Kings College London (KCL) and colleagues used a statistical and computationally efficient approach to predict glacier and ice sheet contributions to sea level rise under a range of scenarios.

They found that if warming was limited to 1.5°C, the contribution of land ice to sea levels could be halved by 2100, limiting sea level rise to 13 centimetres, as opposed to the currently projected 25 centimetres. They also found, however, that in the worst-case-scenario predictions of current warming, Antarctic ice loss could be five times higher, adding 42 centimetres of sea level if nothing is done to curb CO2 emissions.

In the second paper, Robert DeConto from the University of Massachusetts, Amherst (US) and colleagues found that limiting warming to the Paris Agreement’s alternative target of 2°C would maintain consistent Antarctic ice loss at current rates.

Alarmingly, the team also found that at 3°C of warming – the rate our current emissions put us on track for – sea level rise will begin to escalate drastically by 2060, past which the consequences would be “irreversible on multi-century timescales”.

“These results demonstrate the possibility that unstoppable, catastrophic sea level rise from Antarctica will be triggered if Paris Agreement temperature targets are exceeded,” the authors write in their paper.

The implications become even starker on longer timescales: according to DeConto and colleagues, Antarctica will contribute one metre of sea level rise by 2300 if warming is limited to 2°C or less, but if we fail to mitigate emissions, Antarctica may contribute up to 10 metres or more in the next 300 years – which would bring about catastrophic changes to coastal populations around the world.

“Ice-sheet collapse is irreversible over thousands of years, and if the Antarctic ice sheet becomes unstable it could continue to retreat for centuries,” says co-author Daniel M. Gilford from Rutgers University in New Brunswick. “That’s regardless of whether emissions mitigation strategies such as removing carbon dioxide from the atmosphere are employed.”

DeConto and colleagues have also detailed the unique architecture of the Antarctic ice sheet that makes it particularly vulnerable to rising temperatures. The ice sheet flows downhill at a slow rate, and creeps into the ocean where it melts. Currently, the ice sheet is buttressed by a ring of ice shelves that scrape slowly past the shallow sea floor, holding back the upstream ice like a natural dam.

Icebergs in sermilik fjord se greenland. Image jpeg small
Icebergs in Sermilik Fjord, SE Greenland. Credit: Donald Slater

As warming increases, these shelves become thinner and more fragile, ultimately disintegrating and releasing a ‘tide’ of ice, hastening sea level rise. This effect is already observable in Greenland today, but has not yet taken hold in Antarctica.

The results of both studies emphasise that aggressive efforts to curb greenhouse gas emissions are critical to curtail the most damaging effects of climate change and ice sheet loss.

But adhering to strict targets can be a challenge when the impacts appear psychologically distant – whether geographically or temporally. There’s a body of evidence that behaviour change – on an individual and a collective scale – is less likely when this psychological distance from the problem comes into play.

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