Antarctic Sea Ice Hits Once-Per-2.7-Million-Year 'Six Sigma' Event

Antarctic sea ice has hit another record low, dropping into a "six sigma" event.

This means the amount of sea ice in the Antarctic has dropped by more than six standard deviations below the daily mean average for 1991 to 2020.

This drastic reduction can be seen in a graphic created by Eliot Jacobson, a retired professor of mathematics and computer science, using data from Japan's National Institute of Polar Research.

Jacobson posted his chart on Twitter, where it was shared by climate journalist John Gibbons, who tweeted: "Not to be alarmist but...this is what's called a six-sigma event, now unfolding in Antarctica. Otherwise known as a once-in-7.5-million-year event."

Jacobson and Gibbons then began discussing the statistics on Twitter, eventually agreeing that it was "about a 1-in-2.7m year event."

This comes after Antarctic sea ice reached record lows during the winter, which runs from about March to September.

On July 19, the number of square miles of ice was around 772,000 lower than at the same time last year, according to data from the Climate Reanalyzer by the University of Maine.

"Sea ice around the Antarctic has taken a nosedive in the last few years, plummeting faster than any other time since observations began," Ella Gilbert, a climate scientist and presenter, previously told Newsweek.

"It's still too early to say conclusively whether this is a blip in the record or part of an emerging trend, but we expect sea ice to decline in a warming Antarctic."

"Sea ice is sandwiched between a warming atmosphere and ocean, so is sensitive to changes from above and below, although it has previously proved difficult to predict because there are so many complex factors at play," Gilbert said.

"Despite this complexity, it seems likely that Antarctic sea ice will begin to mirror its northern counterpart as human activity continues to change our climate."

The causes of this year's sea ice decline are unclear, but it is thought to be a combination of changes in the atmosphere and increased ocean temperatures.

"The whole system that we are looking at, we know it's strongly coupled," Petra Heil, a sea ice physicist from the Australian Antarctic Division, told ABC Australia.

"Any change in any of the components, even in a region far away or it might be close by in the region that you are studying, is coupled to the whole system. We know that there's a lot more energy at the moment in our weather systems, so they obviously can contribute extensively to moving the sea ice and also be bringing different thermodynamic regimes to the sea ice."

Antarctica is losing around 150 billion tons of ice per year, according to NASA.

The decline is largely down to human action, Heil added. "The consensus statement at the moment would be that this is largely anthropogenic forces that have caused the ocean to warm, for the atmosphere to be highly disturbed and to affect the sea ice," she said.

Antarctic sea ice is incredibly important to the world's climate and ecosystems, as it helps to regulate the Earth's temperature using ice-albedo feedback, with the white ice reflecting the Sun's warmth back out into space. If the ice melts, this heat will be absorbed instead.

The ice is also home to a huge number of species, including marine mammals and penguins. The annual cycle of the Antarctic ice melting and re-freezing drives global currents that transport nutrient-rich water around the world, feeding important ecosystems. If the ice doesn't re-freeze, this effect will be stymied.

Additionally, melting sea ice contributes to global sea level rise, which is expected to displace millions of people around the world, mostly in developing nations.

Many scientists fear we have reached a point of no return for Antarctic sea ice, having heated the Earth to a point where it may be very difficult to reverse the trajectory of sea ice melt.

"We might end up in a new state," Heil said. "That would be quite concerning to the sustainability of human conditions on Earth, I suspect.

"I think a lot of people have the timeline too long out, saying this won't affect them. I'm pretty convinced that this is something my generation will experience."

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