Sea levels may rise much faster than predicted because climate models have failed to account for the disruptive effects of stronger westerly winds, Australian-led research has found.
Recent studies of Antarctica have suggested the giant glaciers of West Antarctica may have begun an irreversible melting that will raise sea levels by as much as 3 metres over 200-500 years.
That estimate, though, may prove optimistic because models had failed to account for how strengthening westerly winds in the Southern Ocean would start to impinge coastal easterlies, upsetting a delicate balance of warm and cold waters close to the Antarctic ice sheets, said Paul Spence, an oceanographer at the University of NSW’s Climate Change Research Centre.
“It’s the first time that I looked at my science and thought, 'Oh my god, that is very concerning'!”, he said. “You hope it’s wrong and you hope it doesn’t happen.
“If you were buying land in Australia and wanting to pass it down to your kids or your grandchildren, I suggest it’s a couple of metres above sea-level,” Dr Spence said.
The research, published in Geophysical Research Letters, found that the coastal temperature structure was more sensitive to global warming, particularly the changes to winds, than previously identified.
“The dynamic barrier between cold and warm water relaxes, and this relatively warm water just offshore floods into the ice-shelf regions, increasing the temperatures by 4 degrees under the ice shelf,” he said.
“If you look at how sensitive the coastal ocean is to these changing winds, you could put a lot more heat under these ice shelves than people have previously thought,” Dr Spence said.
A study released earlier this year by UNSW’s Matt England – also an author on this new research – found westerly winds in the Southern Ocean had quickened 10-15 per cent over the past 50 years, and shifted 2 to 5 degrees closer to the South Pole.
The ozone hole over Antarctica is one factor contributing to the changing winds, along with greenhouse gas emissions, Professor England’s paper found. While the recovery of the ozone layer in coming decades – as fewer ozone-depleting chemicals are released – will slow the wind, any slack would likely be taken up by rising levels of carbon dioxide and other greenhouse gases.
Dr Spence said his team’s study was based on more than 30 models used by the Intergovernmental Panel on Climate Change, and turned up results that shocked the researchers.
The new modelling shows it doesn’t take much additional wind to the system “to really, dramatically upset" conditions, he said. “It’s a system really dramatically ripe for change.”
Tas van Ommen, a principal research scientist at the Australian Antarctic Division, said the research helped explain the mechanism that is causing the rapid melting of the West Antarctic glaciers now being observed.
“This paper is a necessary first step to actually closing some the understanding gaps,” Dr van Ommen said.
While predictions of future sea-level rise were difficult to make, “adding a few tenths of a metre from ice instability this century is a significant concern”, he said.
Even 10 centimetres of sea-level rise tripled the flooding frequency of the world’s coastal regions, he said.