Wednesday, August 9, 2023

Antarctic sea ice levels dive in 'five-sigma event', as experts flag worsening consequences for planet

The extent of sea ice around Antarctica is falling off a cliff this winter, with Australian scientists now concerned it may not recover.
Ice levels have not returned to the Antarctic over winter — and experts are very concerned.

From ABC by Alexandra Alvaro
Antarctic sea ice has usually been able to recover in winter.
But this year, sea ice has not returned to expected levels during winter
What's next? Experts say if the sea ice trend continues, it will accelerate the warming of the planet

This winter has confirmed what scientists had feared — the sea ice around Antarctica is in sharp decline, with experts now concerned it may not recover.

Earlier this year, scientists observed an all-time low in the amount of sea ice around the icy continent, following all-time lows in 2016, 2017 and 2022.

Usually, the ice has been able to recover in winter, when Antarctica is reliably dark and cold.

But this year is different.
For the first time, the sea ice extent has been unable to substantially recover this winter, leaving scientists baffled.
'Five-sigma' event unfolding

Physical oceanographer Edward Doddridge has been communicating with scientists and the community about the drastic changes happening around Antarctica.

He said vast regions of the Antarctic coastline were ice free for the first time in the observational record.
"To say unprecedented isn't strong enough," Dr Doddridge said.
"For those of you who are interested in statistics, this is a five-sigma event.
So it's five standard deviations beyond the mean.
Which means that if nothing had changed, we'd expect to see a winter like this about once every 7.5 million years.
"It's gobsmacking."

Edward Doddridge says of the ice returning next winter: "We can hope.
I don't know that it will." (ABC News: Jordan Young)

Sea ice is important for a number of reasons.

First, it helps regulate Earth's temperature through something called ice-albedo feedback, where the ice reflects the Sun's heat back into space, helping to regulate the temperature of the planet.
"If there's less ice, then the sunlight that hits the ocean's surface is absorbed instead of being reflected out into space," Dr Doddridge said.
"That accelerates the warming in that area, and that warmth then gets carried around to the rest of the world."

One expert says a further change in the balance could trigger a tipping point, and that "we might end up in a new state".
(Supplied: Australian Antarctic Division)

Second, the annual cycle of freeze and melt drives global currents that transport nutrient-rich water into the rest of the ocean, feeding ecosystems.

The ice is also a habitat for animals such as penguins and seals, and is essential for smaller creatures such as krill, which feed on the algae underneath the ice during winter.

One scientist says if the sea ice downward trend continues, it will be "difficult to reverse the trajectory".(Supplied: Australian Antarctic Division)

Scientists are now scrambling to work out what is causing the dip.
Is it natural variability? Or is climate change responsible?

Dr Doddridge said it was more likely the latter.

"There are people saying it could be natural variability," he said.
"Absolutely we can't conclusively rule it out yet. But it's very unlikely."
"It is most definitely a window into the future.
"We know that this is what the world is going to look like as it warms.
"It may be that next winter it comes back. We can hope. I don't know that it will."

On top of that, scientists do not know where the change is coming from — the seas or the atmosphere.

Dr Doddridge believes it is due to changes in sea temperatures — but Petra Heil, a sea ice physicist from the Australian Antarctic Division, is of the opinion it is due to a combination of both changes in the atmosphere and warming seas.
"The whole system that we are looking at, we know it's strongly coupled," Dr Heil said.
"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."

Sea ice physicist from the Australian Antarctic Division, Dr Petra Heil.
(Australian Antarctic Program: Petra Heil)

But Dr Heil agreed with Dr Doddridge that the root cause most likely originated from human activity.

"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.

Either way, she fears a further change in the balance could trigger a tipping point from where it's difficult to reverse the trajectory.

"We might end up in a new state," she said.
"That would be quite concerning to the sustainability of human conditions on Earth, I suspect.
"I think a lot of people have the time line 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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