Arctic’s coldest sea ice is vulnerable to melting

For the walrus and other species that rely on the floes, the fate of the Last Ice Refuge is critical. Image: By NOAA (public domain), via Wikimedia Commons

Every year an ice floe as big as Austria simply vanishes. That’s climate change, as the Arctic’s coldest sea ice risks melting.

LONDON, 6 July, 2021 − The frozen world is dwindling fast. New research suggests that the cryosphere − the area of the planet covered by snow and ice − is dwindling by around 87,000 square kilometres every year. This is an area bigger than Austria, almost as big as Hungary, or Jordan. Even the Arctic’s coldest sea ice is threatened.

A second, separate study warns that what glacier scientists call the Last Ice Refuge − the tract of Arctic Ocean that will stay frozen when the rest of it becomes open water during some summers in the next decades − is itself at risk: the coldest and most secure reaches of sea ice just north of Greenland and Canada could be vulnerable to summer melt.

That the polar regions and the high-altitude frozen rivers and lakes are at risk is not news: climate scientists have been warning for decades of accelerating melt in Antarctica, ever-higher losses of ice mass from Greenland, and a loss of northern polar sea ice so comprehensive that by 2050, much of the Arctic Ocean could be clear blue water most summers.

The cryosphere matters: it is a reservoir of two-thirds of the planet’s fresh water. Its gleaming white surface acts as planetary insulation: most of the sunlight that falls upon it is reflected back into space. As the ice thins and retreats, the exposed darker ocean below it warms up, to accelerate global heating and trigger yet more ice loss.

“In years when you replenish the ice cover in this region with older, thicker ice, that doesn’t seem to help as much as you might expect”

Scientists from Lanzhou University in China report in the journal Earth’s Future that they tried to look at the picture of change on a planetary scale. The cryosphere has always expanded and shrunk with the seasons in both hemispheres. Scientists calculated the daily extent of all the world’s snow and ice cover and then averaged it to get yearly estimates.

The Arctic is perhaps the fastest-warming zone on the planet and the northern hemisphere cover has been losing 102,000 sq kms a year, every year. This is an area bigger than Iceland, or Eritrea. The southern hemisphere ice however has been expanding by about 14,000 sq kms a year − think of the Bahamas − to offset a little of the loss.

The researchers also found that much of the cryosphere was now frozen for shorter periods: the day of first freezing now happens about 3.6 days later than it did in 1979, and the ice thaws 5.7 days earlier than it did 40 years ago.

But until now, one stretch of Arctic sea ice had shown no particular signs of change. When glaciologists repeatedly warned that the Arctic could be ice-free in summer by mid-century, they meant that the region would be down to its last million sq km of ice floe. This would be the last stronghold of the frozen world: the last place where seals, walruses and polar bears could find the surfaces they needed for survival.

Essential Refuge

But researchers aboard the German icebreaker Polarstern observed that the ice cover of the Wandel Sea off Greenland and Canada in the summer of 2020 was at a record low. This was a surprise, because at the beginning of the season it had been as dense as ever.

Permanent ice is a matter of life and death to the Arctic’s apex mammal predators: seals haul out onto the ice, to become potential prey for polar bears. Walruses use the ice as a platform for foraging. As the summer sea ice thins and shrinks a little more every year over the rest of the Arctic, the Last Ice Refuge becomes ever more important for their survival as species. The big question is: were the weather conditions unusual, or was this a sign of global heating?

“During the winter and spring of 2020 you had patches of older, thicker ice that had drifted into there, but there was enough thinner, newer ice that melted to expose open ocean,” said Axel Schweiger of the University of Washington in the US, who led the research.

“That began a cycle of absorbing heat energy to melt more ice, in spite of the fact that there was some thick ice. So in years when you replenish the ice cover in this region with older, thicker ice, that doesn’t seem to help as much as you might expect.” − Climate News Network