Hitting Paris climate goal could cut sea level rise in half by 2100

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Sea level rise caused by melting glaciers and ice sheets could be cut in half if the toughest Paris goals are met

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The amount of sea level rise facing coastal cities as a result of ice melt could be roughly halved if the world meets the Paris Agreement’s toughest goal of holding climate change to 1.5°C of warming.

Coastal flooding would still worsen as meltwater from glaciers and ice sheets would raise seas by an average 13 centimetres by 2100, a new overview of computer modelling suggests. But failure to rein in carbon dioxide emissions leading to global warming of 3.4°C would see a 25-cm increase from ice melt.

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“We know global sea level is going to continue to rise. But we could halve that contribution from ice melting if we limit warming to 1.5°C above pre-industrial [levels]. Of course, coastal flooding will still increase, but less severely,” says Tamsin Edwards at King’s College London.

Edwards and her colleagues analysed the results of hundreds of ice and climate change models to see how loss of land ice across 19 regions of the world may affect sea level rise between 2015 and 2100 under two plausible emissions scenarios.

Curbing temperature rises makes a big difference to how much melting glaciers around the world and ice sheets on Greenland raise seas. But the new analysis notably shows the same impact from Antarctica – 5 centimetres of sea level rise per century – whether temperatures are held to 1.5°C or 3.4°C.

Edwards say this is “not because we don’t think Antarctica will respond to climate change”. Instead, there was such a wide range of results in models – from ones where extra snowfall in a warming world offsets ice melt from oceans warming, and vice versa – that it isn’t clear what Antarctica will do.

Jonathan Bamber at the University of Bristol in the UK says the research is thorough and careful. However, he notes that none of the study’s models include a process called marine ice cliff instability, a theoretical but as-yet unseen process that could lead Antarctica’s ice sheets to disintegrate faster. “Ice sheets can behave in unexpected ways,” he says.

The average rates of ice loss expected each century by the team are generally lower than those of major reports by the Intergovernmental Panel on Climate Change in 2019 and 2014. However, Edwards says that factoring in uncertainties around projections, her team’s findings should be seen as broadly consistent with the IPCC. The new results will feed into the next IPCC report, the sixth assessment, the first part of which is due to be published in August.

Eric Rignot at the University of California, Irvine, who wasn’t involved in the research, says the models’ predictions remain much lower than the 80-cm sea level rise the planet is on track for based on observations. “This study does not change my view that these model projections of sea level change are woefully optimistic,” he says.

Journal reference: Nature, DOI: 10.1038/s41586-021-03302-y

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