Antarctic sea ice at ‘astonishing’ low warning experts
- Written by Georgina Ranard, Becky Dale and Erwan Revolt
- BBC News climate, science and data journalism team
Satellite data shows that the sea ice surrounding Antarctica is far below any previous recorded winter level, a worrying new indicator for a region that once seemed resistant to global warming.
“It’s so far beyond anything we’ve seen, it’s almost astonishing,” says Walter Mayer, who monitors sea ice at the National Snow and Ice Data Center.
Polar experts warn that Antarctica’s instability could have far-reaching consequences.
Antarctica’s huge expanse of ice regulates the planet’s temperature, as the white surface reflects the sun’s energy back into the atmosphere and also cools the water below and near it.
Without ice to cool the planet, Antarctica could turn from Earth’s refrigerator into a cooler, experts say.
The area of ice now floating on the surface of the Antarctic Ocean is less than 17 million square kilometers – that is 1.5 million square kilometers of sea ice less than the September average, and well below record winter lows.
This is an area of lost ice about five times the size of the British Isles.
Dr. Mayer is not optimistic that sea ice will recover significantly.
Scientists are still trying to determine all the factors that led to the decline in sea ice this year, but studying trends in Antarctica has been historically difficult.
“We can see how vulnerable it is,” says Dr. Robbie Mallett, of the University of Manitoba, who is based on the Antarctic Peninsula.
Challenged by isolation, extreme cold and strong winds, this year’s thin sea ice made his team’s work more difficult. “There is a risk that it will break and drift out to sea and we are on it,” says Dr. Mallett.
Sea ice forms in the continent’s winter (March to October) before largely melting in the summer, and is part of an interconnected system that also consists of icebergs, land ice and massive ice shelves – floating extensions of land ice jutting out from the coast.
Sea ice acts as a protective blanket of ice that covers the land and prevents the ocean from heating.
Dr Caroline Holmes of the British Antarctic Survey explains that the effects of shrinking sea ice may become apparent as the season moves into summer – when there is the potential for an unstoppable feedback loop of ice melt.
As more sea ice disappears, it exposes dark areas of the ocean, which absorb sunlight rather than reflect it, adding thermal energy to the water, which in turn melts more ice. Scientists call this the ice albedo effect.
This could add more heat to the planet, disrupting Antarctica’s usual role as a global temperature regulator.
“Shall we wake this giant in Antarctica?” asks Professor Martin Siegert, a glaciologist at the University of Exeter. He says that would be “an absolute disaster for the world.”
Professor Anna Hogg, an earth scientist at the University of Leeds, says there are signs that what is actually happening to Antarctica’s ice sheets is in the worst-case scenario range than expected.
Even modest increases in sea levels can lead to dangerously high storm surges that can wipe out coastal communities. If large amounts of land ice began to melt, the effects would be catastrophic for millions of people around the world.
“We never thought that extreme weather events could happen there.”
As an independent continent surrounded by water, Antarctica has its own weather and climate system. Until 2016, the extent of Antarctica’s winter sea ice was actually growing.
But in March 2022, an intense heatwave hit East Antarctica, pushing temperatures to -10°C when they should have been closer to -50°C.
“When I started studying Antarctica 30 years ago, we never thought that extreme weather events could occur there,” says Professor Siegert.
Antarctica’s remoteness and lack of historical information means that much remains unknown.
The region still represents the “Wild West” in scientific terms, according to Dr. Robbie Mallett.
Scientists know how widespread sea ice is, but they don’t know, for example, how thick it is. Solving this puzzle could radically change climate models in the region.
At Rothera Science Base, Dr Mallett is using radar instruments to study the thickness of sea ice for an international research project called Defiant.
He and other scientists are still trying to uncover the reasons for the disappearance of winter ice.
“There’s a possibility that this is a strange expression of natural fluctuations,” he says, meaning that a lot of natural factors may have built up and are affecting the area at once.
Scientists point out that the oceans, which recorded record high temperatures this year, are likely a contributing factor, as the warm water will not freeze.
There may also have been changes in the ocean currents and winds that drive temperatures in Antarctica.
It is also possible that the El Niño climate phenomenon currently developing in the Pacific region is contributing to the shrinkage of sea ice, although it is still weak.
Dr Mallett says there are “very good reasons to be concerned”.
“It’s potentially a really worrying sign of climate change in Antarctica that wasn’t there 40 years ago. It’s only emerging now.”