If all our fear and uncertainty over climate change could be distilled into a single statistic, then arguably it was delivered to an emergency summit on the future of the Antarctic last month.
Nerilie Abram at the Australian National University, Canberra, opened her presentation with a slide headlined “Antarctic sea ice has declined precipitously since 2014, and in July 2023 exceeded a minus 7 sigma event”.
At times, the noise of the 500 researchers who gathered for the Australian Antarctic Research Conference in Tasmania was overwhelming, as they tried to make sense of the unprecedented shifts underway at the bottom of the globe. But as Abram’s slide sunk in, it was as if the whole room was holding its breath.
Put simply, a minus 7 sigma event, meaning seven standard deviations below the average, should be all but impossible, says Ed Doddridge at the Australian Antarctic Program Partnership, who works with Abram.
It is “actually really hard to convey just how extreme this difference was, how extreme the low sea ice extent was”, he says. One way is to liken it to the concept of a one-in-100-year flood, for example. “If you run those sorts of statistics for Antarctic sea ice last year, you get a number somewhere between one in 7.5 million years and one in 700 billion years,” says Doddridge.
Of course, given this event has occurred, something must be wrong with our models. They just aren’t able to predict how radically and possibly permanently the Antarctic environment has changed, he says.
The entire Antarctic research community is now scrambling to understand what will happen to the sea ice in the coming years and what the implications will be for everything from local ecosystems to global weather.
So just how bad is it? According to the US National Snow and Ice Data Centre, the 7 sigma event was the lowest maximum since records began in 1979. This year was the second lowest, with Antarctic sea ice “stalling out” at a maximum extent of 17.16 million square kilometres, or just 200,000 square kilometres more than last year.
Remarkably, that is 1.55 million square kilometres below the expected average extent. In other words, in the past two years an area of ice nearly 6.5 times the size of the UK has disappeared. Another way to imagine it is that the ring of sea ice that forms every winter around the entire Antarctic continent has contracted by an average of 120 kilometres, says Abram.
While much of the world’s focus has been on the loss of winter sea ice in the Arctic, Abram told the conference, in just a decade the decrease in the Antarctic is equivalent to that lost in the northern hemisphere in the past 45 years. Even more alarming is the projection that Antarctica could possibly experience summers that are essentially free of sea ice before even the Arctic, which is projected to reach that point before 2050.
Though warm ocean waters mostly explain the retreats along West Antarctica, large retreats along the northeast side of the Antarctic Peninsula are more difficult to interpret.
https://eos.org/research-and-developments/antarctic-ice-sheet-has-lost-a-connecticut-sized-amount-of-ice-over-the-past-30-years