Sea ice surrounding Antarctica is well below any previously recorded winter levels, satellite data shows, a worrying new benchmark for a region that once seemed resistant to global warming.
“It’s so far from anything we’ve seen, it’s almost mind-blowing,” says Walter Meier, who monitors sea ice with the National Snow and Ice Data Center.
An unstable Antarctica could have far-reaching consequences, polar experts warn.
Antarctica’s huge ice sheet regulates the planet’s temperature, as the white surface reflects the Sun’s energy into the atmosphere and also cools the water beneath and near it.
Without ice cooling the planet, Antarctica could turn from Earth’s refrigerator to a radiator, experts say.
Ice floating on the surface of the Southern Ocean now measures less than 17 million square km, which is 1.5 million square km of sea ice less than the September average and well below previous winter record lows.
This is an area of missing ice about five times larger than the British Isles.
Dr. Meier is not optimistic that sea ice will recover to any significant extent.
Scientists are still trying to identify all the factors that led to the reduction in sea ice this year, but studying trends in Antarctica is historically challenging.
In a year when several global heat and ocean temperature records have been broken, some scientists insist that low sea ice is the measure to watch.
“We can see how much more vulnerable it is,” says Dr. Robbie Mallet, of the University of Manitoba, which is based on the Antarctic Peninsula.
Already defying isolation, extreme cold and powerful winds, this year’s thin sea ice made his team’s job even more difficult. “There is a risk that it will break off and drift out to sea with us on board,” says Dr. Mallet.
Sea ice forms during the continent’s winter (March to October) before largely melting in the summer, and is part of an interconnected system that also includes icebergs, land ice, and enormous ice shelves: floating extensions of ice land that protrude from the coast.
Sea ice acts as a protective sheath for the ice that covers the land and prevents the ocean from warming.
Dr Caroline Holmes of the British Antarctic Survey explains that the impacts of shrinking sea ice could become apparent as the season shifts to summer, when there is the potential for an unstoppable feedback loop of melting ice.
As sea ice disappears, it exposes dark areas of the ocean, which absorb sunlight instead of reflecting it, meaning heat energy is added to the water, which in turn melts more ice. Scientists call this phenomenon the ice-albedo effect.
This could add much more heat to the planet, disrupting Antarctica’s usual role as a regulator of global temperatures.
“Are we awakening this Antarctic giant?” asks Professor Martin Siegert, a glaciologist at the University of Exeter. It would be “an absolute disaster for the world,” he says.
There are signs that what is already happening to Antarctica’s ice sheets is a worse-than-expected scenario, says Professor Anna Hogg, an Earth scientist at the University of Leeds.
Since the 1990s, land ice loss from Antarctica has contributed 7.2 mm to sea level rise.
Even a modest rise in sea levels can cause dangerously high storm surges that could wipe out coastal communities. If significant amounts of land ice began to melt, the impacts would be catastrophic for millions of people around the world.
“We never thought that extreme weather events could occur there”
As a self-contained continent surrounded by water, Antarctica has its own weather and climate system. As recently as 2016, Antarctica’s winter sea ice was actually growing.
But in March 2022 an extreme heat wave 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.
Sea ice has exceeded record lows in summer for three of the last seven years, including February 2023.
Some scientists even believe that these low ice levels may indicate that a fundamental change is taking place on the continent: a change in the conditions that have kept the region isolated.
The remoteness of Antarctica and the dearth of historical information mean that much is still unknown.
According to Dr. Robbie Mallet, the region is still the “Wild West” in scientific terms.
Scientists know how long sea ice extends, but not, for example, how thick it is. Unlocking this puzzle could fundamentally change the region’s climate patterns.
At the Rothera science base, Dr. Mallet studies the thickness of sea ice with radar instruments for an international research project called Defiant.
He and other scientists are still trying to unravel the causes of the disappearance of winter ice.
“There’s a possibility that this is a really bizarre expression of natural variability,” he says, meaning that many natural factors could have accumulated and affected the region at the same time.
This year’s warmer oceans are likely a contributing factor, scientists suggest: The warm water won’t freeze.
And there may also have been changes in ocean currents and winds that drive temperatures in Antarctica.
The El Niño weather phenomenon, which is currently developing in the Pacific, could also subtly contribute to the reduction of sea ice, although it is still weak.
Dr Mallet says there are “very good reasons to be concerned”.
“It’s potentially a really alarming sign of climate change in Antarctica that hasn’t happened in the last 40 years. And it’s only emerging now.”