Polar ice melting faster and faster

 

When the sea ice melts there is nothing to prevent Antarctic glaciers from accelerating their pace towards the ocean. Image: NOAA NMFS SWFSC Antarctic Marine Living Resources (AMLR) Program

From Climate News Network

An Antarctic glacier has begun to move more quickly towards the open ocean, as the shelf of sea ice that once held it back starts to collapse. The water in that one glacier is enough to raise global sea levels by half a metre. And that’s not all that’s raising polar concerns across the scientific world.

At the other end of the Earth global heating is accelerating the loss of Arctic ice. A new study reports that the thinning of sea ice in three separate coastal regions could now be happening twice as fast.

Both findings are linked to the inexorable rise in global average temperatures as the profligate use of fossil fuels heightens the ratio of greenhouse gases in the planet’s atmosphere.

Antarctic scientists have been worrying about warming in Antarctica for years. And they have been anxiously watching the Pine Island glacier in West Antarctica for decades.

Glaciers move at the proverbial glacial pace towards the sea, to be held in check, in the polar oceans, by vast shelves of sea ice. Between 2017 and 2020 the ice shelves have undergone a series of collapses and lost one fifth of their area, possibly because the glacier has been accelerating.

“We may not have the luxury of waiting for slow changes on Pine Island; things could actually go much quicker than expected,” said Ian Joughin, of the University of Washington in the US.

“The processes we’d been studying in this region were leading to an irreversible collapse, but at a fairly measured pace. Things could be much more abrupt if we lose the rest of that ice shelf.”

He and his colleagues report in the journal Science Advances that the Pine Island glacier has already become Antarctica’s biggest contributor to sea level rise. The pace of flow remained fairly steady from 2009 to 2017, but they found that data from Europe’s Copernicus Sentinel satellite system showed an acceleration of 12% in the past three years.

The Pine Island glacier contains roughly 180 trillion tonnes of ice, enough to raise global sea levels by 0.5 metres. Researchers had calculated that it might take a century or more for slowly-warming polar waters to thin the ice shelves to the point where they could no longer stem the glacier flow. But it now seems that the big player in the shelf ice collapse is the glacier itself, as the flow rate increases.

“The loss of Pine Island’s ice shelf now looks possibly like it could occur in the next decade or two, as opposed to the melt-driven sub-surface change playing out over more than 100 or more years,” said Pierre Dutrieux of the British Antarctic Survey, a co-author. “So it’s a potentially much more rapid and abrupt change.”

Abrupt change, too, may be on the way in the Arctic Ocean. British researchers used a new computer simulation to explore measurements from Europe’s CryoSat-2 satellite. The scientists report in the journal The Cryosphere that the thinning of ice in the Laptev and Kara Seas north of Siberia, and the Chukchi Sea between Siberia and Alaska, has stepped up by 70%, 98% and 110% respectively.

Sea ice diminishes each summer and forms again each winter; each successive summer reveals an ever-greater loss, as the ice itself thins and the area covered by ice dwindles.

Calculations of ice thickness have always allowed for the falls of fresh winter snow. But since the formation of sea ice has been later every year, there has been less time for the snow to accumulate. Such things make a difference.

“The thickness of the sea ice is a sensitive indicator of the health of the Arctic,” said Robbie Mallett, of University College London.

“It is important as thicker ice acts as an insulating blanket, stopping the ocean from warming up the atmosphere in winter, and protecting the ocean from sunshine in summer. Thinner ice is also less likely to survive the summer melt.”