There is about 10 per cent less sea ice in Antarctica this year than the previous record minimum - a stunning reversal after new highs were set in 2014.
The sea ice extent around the southern continent dropped to 2.135 million square kilometres on Sunday, and expanded 25,000 square kilometres the following day, indicating the freezing season has likely begun, said Jan Lieser, a sea ice scientist at the Hobart-based Antarctic Climate and Ecosystems Co-operative Research Centre.
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| Antarctic sea ice swings from record large extent to record lows in just two and a half years. Photo: Ross Norton |
Australasian Antarctic Expedition - Sir Douglas Mawson
Australian geologist Sir Douglas Mawson led the Australasian Antarctic Expedition (AAE); an Australasian scientific team that explored part of Antarctica between 1911 and 1914. Video courtesy of Mawson Huts Foundation.
The switch from a sea-ice maximum around Antarctica to its annual low is "one of the biggest natural cycles we see in the world", with as much as 90 per cent of the ice only a year old at the most, he said.
Reliable satellite records only go back to 1979, and it's harder to access ice thickness compared with the North Pole, with Arctic ice mostly accessible from above or via submarine below.
In the southern winter of 2014, sea ice around Antarctica reached a record large extent. At the time, climate change sceptics were keen to highlight the increase in the south as a counterpoint to the more steadily decreasing Arctic ice.
'Along came 2016'
"[Sea-ice] variability was typical of what we'd seen for the whole period [since 1979], but then along came 2016," said Ian Simmonds, from the School of Earth Sciences at the University of Melbourne. "It's remarkable."
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| Adult humpback whale breaching in the Gerlache Strait, Antarctica: More room to move than in any previous year on record. Photo: Michael Nolan |
(See chart below from the US National Snow and Ice Data Center, showing how rapidly ice coverage anomalies shifted.)
Sea ice is now at record lows at both ends of the planet, exposing more of the dark seas to solar radiation, rather it being reflected back to space.
The lack of ice will likely add to the build-up in heat in the oceans that could hinder ice recovery in the south and accelerate the melt in the north as seasons shift towards winter and summer, respectively.
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| Arctic Sea Ice Extent/Concentration |
While the loss of floating ice doesn't affect sea levels, its absence leaves shore-based ice shelves exposed to faster melting and accelerated glacier movement. "It opens up the vulnerability of the ice shelves around there," Dr Lieser said.
Professor Simmonds said several factors were at play in the Antarctic, such as the strengthening of westerly winds that tend to push sea-ice northwards.
Countering that, though, was the long-anticipated thermodynamic effect that warming ocean temperatures - with the Southern Ocean a major heat sink globally - would limit sea ice growth by melting the bergs from below.
While it's too early to tell whether the second effect is becoming a dominant factor during the current ice retreat, long-term climate models suggest that it will play the major role at some point, Professor Simmonds said..
Antarctic temperatures - along with those in the high Arctic - have been among the fastest rising anywhere, as rising greenhouse gases drive climate change.
Gwen Fenton, chief scientist of the Australian Antarctic Division, told Senate estimates on Monday that air over the Antarctic Peninsula had warmed about 2.8 degrees over the past 50 years alone.
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