As the Northern Hemisphere swelters under a record-breaking summer heat wave, much further south, in the depths of winter, another terrifying climate record is being broken. Antarctic sea ice has fallen to unprecedented lows for this time of year.
Every year, Antarctic sea ice shrinks to its lowest levels towards the end of February, during the continent’s summer. The sea ice then builds back up over the winter.
But this year scientists have observed something different.
The sea ice has not returned to anywhere near expected levels. In fact it is at the lowest levels for this time of year since records began 45 years ago. The ice is around 1.6 million square kilometers (0.6 million square miles) below the previous winter record low set in 2022, according to data from the National Snow and Ice Data Center (NSIDC).
In mid-July, Antarctica’s sea ice was 2.6 million square kilometers (1 million square miles) below the 1981 to 2010 average. That is an area nearly as large as Argentina or the combined areas of Texas, California, New Mexico, Arizona, Nevada, Utah, and Colorado
‘The game has changed’
The phenomenon has been described by some scientists as off-the-charts exceptional – something that is so rare, the odds are that it only happens once in millions of years.
But Ted Scambos, a glaciologist at the University of Colorado Boulder, said that speaking in these terms may not be that helpful.
“The game has changed,” he told CNN. “There’s no sense talking about the odds of it happening the way the system used to be, it’s clearly telling us that the system has changed.”
Scientists are now scrambling to figure out why.
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The Antarctic is a remote, complex continent. Unlike the Arctic, where sea ice has been on a consistently downwards trajectory as the climate crisis accelerates, sea ice in the Antarctic has swung from record highs to record lows in the last few decades, making it harder for scientists to understand how it is responding to global heating.
But since 2016, scientists have begun to observe a steep downwards trend. While natural climate variability affects the sea ice, many scientists say climate change may be a major driver for the disappearing ice.
“The Antarctic system has always been highly variable,” Scambos said. “This [current] level of variation, though, is so extreme that something radical has changed in the past two years, but especially this year, relative to all previous years going back at least 45 years.”
Several factors feed into sea ice loss, Scambos said, including the strength of the westerly winds around Antarctica, which have been linked to the increase of planet-heating pollution.
“Warmer ocean temperatures north of the Antarctic Ocean boundary mixing into the water that’s typically somewhat isolated from the rest of the world’s oceans is also part of this idea as to how to explain this,” Scambos said.
In late February of this year, Antarctic sea ice reached its lowest extent since records began, at 691,000 square miles.
This winter’s unprecedented occurrence may indicate a long-term change for the isolated continent, Scambos said. “It is more likely than not that we won’t see the Antarctic system recover the way it did, say, 15 years ago, for a very long period into the future, and possibly ‘ever.’”
Others are more cautious. “It’s a large departure from average but we know that Antarctic sea ice exhibits large year to year variability,” Julienne Stroeve, a senior scientist at the National Snow and Ice Data Center told CNN, adding “it’s too early to say if this is the new normal or not.”
Cascading effects
Sea ice plays a vital role. While it doesn’t directly affect sea level rise, as it’s already floating in the ocean, it does have indirect effects. Its disappearance leaves coastal ice sheets and glaciers exposed to waves and warm ocean waters, making them more vulnerable to melting and breaking off.
A lack of sea ice could also have significant impacts on its wildlife, including krill on which many of the region’s whales feed, and penguins and seals that rely on sea ice for feeding and resting.
More broadly, Antarctica’s sea ice contributes to the regulation of the planet’s temperature, meaning its disappearance could have cascading effects far beyond the continent.
The sea ice reflects incoming solar energy back to space, when it melts, it exposes the darker ocean waters beneath which absorb the sun’s energy.
Parts of Antarctica have been seeing alarming changes for a while. The Antarctic Peninsula, a spindly chain of icy mountains which sticks off the west side of the continent, is one of the fastest warming places in the Southern Hemisphere.
Last year, scientists said West Antarctica’s vast Thwaites Glacier – also known as the “Doomsday Glacier” – was “hanging on by its fingernails” as the planet warms.
Scientists have estimated global sea level rise could increase by around 10 feet if Thwaites collapsed completely, devastating coastal communities around the world.
Scambos said that this winter’s record low level of sea ice is a very alarming signal.
“In 2016, [Antarctic sea ice] took the first big down-turn. Since 2016, it’s remained low, and now the bottom has fallen out. Something major in a huge part of the planet is suddenly behaving differently from what we saw for the past 45 years.”
CNN’s Laura Paddison contributed to this report.