Antarctic ice may melt faster than thought
Rapid sheet loss could raise sea levels 46 to 86 centimetres more than forecast, study says
WASHINGTON— Warmer air, less frigid water and gravity may combine to make parts of Antarctica’s western ice sheet melt far faster than scientists had thought, raising sea levels much more than expected by the end of the century, according to a new study.
New physics-based computer simulations forecast dramatic increases in melting on the vulnerable western edge of the continent. In a worstcase scenario, that could raise sea levels in 2100 by 46 to 86 centimetres more than an international panel of climate scientists predicted just three years ago.
And even if countries control heattrapping gases at the moderate levels they pledged in Paris last year, it would still mean seas eight to 31 centimetres higher than have been forecast, according to a study published Wednesday in the journal Nature.
By the year 2500, in the worst-case scenario, the simulations predict seas 13 metres higher — purely from Antarctic melt.
“You’re remapping the way the planet looks from space with those numbers, not just subtle changes about which neighbourhoods are going to be susceptible to storm surge,” said Robert DeConto, the study’s lead author and a climate scientist at the University of Massachusetts.
This is all because Antarctica is one of the biggest wild cards when scientists try to assess the effects of manmade climate change in upcoming decades. Scientists were caught by surprise when the western portion of the continent started showing signs of rapid ice loss in the past decade or so.
The United Nations Intergovernmental Panel on Climate Change has not forecast much sea-level rise from Antarctica, just 18 centimetres by 2100 in their last report.
For this century, the panel saw water expanding from heat, glacier melt and Greenland ice sheet loss as bigger factors.
Instead of 18 centimetres, DeConto’s simulations forecast the sea-level rise from Antarctica’s melt alone as 64 to 105 centimetres in the worstcase scenario and 26 to 49 centimetres if greenhouse gas emissions are moderately controlled. If the world cracks down more dramatically on heat-trapping gases, Antarctica would essentially not add anything to sea-level rise, the study said.
But those figures are just worldwide averages. In many places on the U.S. East Coast, such as Boston, it could be 25 per cent more than that because of geological conditions, DeConto said.
“North America has a lot to fear from ice loss from West Antarctica, which is where it all begins,” DeConto said.
While other studies have looked at the effect of warming from water below ice sheets and the air that melts from above, DeConto adds in the effect of pooling water and giant ice cliffs. Those ice cliffs, which can be dozens and even hundreds of feet high, can collapse from the sheer weight of ice and that hastens glacier and ice sheet retreat, he said.
Ted Scambos at the University of Colorado, who wasn’t part of the new study, said it was plausible and used “a few simple yet underappreciated factors regarding ice retreat.”
Carnegie Institute climate scientist Chris Field said the study drives home the difference the world can make by controlling its greenhouse gas emissions.
It’s the difference between rising seas that can be managed and conditions that are “dangerously risky,” he said.