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Earlier this year it was clear Antarctic sea ice levels were low. Now, as the continent enters spring, it’s obvious that “it’s a really exceptional year.”

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Winter is over in the Southern Hemisphere and sea ice around Antarctica has likely grown as much as it’s going to for 2023, according to the National Snow and Ice Data Center. Antarctic sea ice reached its lowest peak by a wide margin for any year since 1979, when the continuous satellite record began.

“The ice this year is so far out of the range of all the other years that it’s a really exceptional year,” said Ariaan Purich, a climate scientist at Monash University in Australia.

By Sept. 10, sea ice had grown to cover 6.5 million square miles around the continent, or just under 17 million square kilometers. The difference this year from the 1981 to 2010 average is an area roughly the size of Alaska.

Why It Matters: Sea ice protects the continent’s ice shelf and wildlife.
Antarctica has ice both on land, in the form of its massive continental ice sheet, and in the waters around it, in the form of seasonal sea ice. The ice in the water helps protect the land ice from the warming ocean. Less sea ice could mean that the continental ice sheet melts and breaks faster, contributing to faster sea-level rise around the world.

That sea ice supports a whole ecosystem of wildlife, including both Adélie and emperor penguins. Last year, several emperor penguin colonies suffered a widespread loss of their chicks when the ice broke up early.

Background: This year’s record low follows several years of decline.
Antarctic sea ice has been growing sluggishly and staying at record lows for each month since April.

“Things got really strange,” said Walt Meier, a senior research scientist at the National Snow and Ice Data Center. “It started diverging from anything we’d seen before.”

Satellite data from 1966 showed a similarly low sea ice extent, but Dr. Meier cautioned that this earlier data is less reliable and should not be used as a direct comparison to today’s observations.

The departure from previous years is particularly significant right now, but follows several years of declining sea ice. Until 2016, the sea ice around Antarctica had remained relatively stable, unlike ice in the Arctic Ocean, even as the global temperature rose. But in the past seven years, Antarctic sea ice has reached record lows numerous times.

What’s Next: A potential new, unstable era for Antarctic sea ice.
A complicated mix of atmospheric and oceanic factors influence how much sea ice forms around Antarctica each year, and scientists still debate the relative importance of each factor. But ocean warming from global climate change seems to be a growing influence, said Dr. Purich, who published a study in September on trends for this year’s Antarctic sea ice, suggesting that Antarctica and the Southern Ocean may be tipping into a new state with persistently low sea ice.

This year’s trends might continue into 2024 thanks to the potential of what’s known as a positive feedback loop. White ice reflects sunlight, while dark ocean water absorbs it. So the less sea ice there is, the more local sea-surface temperatures are likely to rise and melt the ice further, said Marilyn Raphael, a geography professor and director of the Institute of the Environment and Sustainability at University of California, Los Angeles.

She recently helped reconstruct a longer record of Antarctic sea ice that includes seasonal averages stretching back to 1905 using historical weather observations. The average sea-ice cover from June through August this year was far outside any other winter average even in this longer record.

A correction was made on Oct. 5, 2023: An earlier version of this article characterized incorrectly the cycle of melting described by Marilyn Raphael. It is a positive feedback loop (because the product of the reaction leads to an increase in that reaction) not a negative feedback loop.