Scientists say that Antarctic sea ice has been behaving erratically in recent years. (Supplied: AAD/Gemma Woldendorp)
In short:
Scientists have expressed alarm after Antarctic sea ice again fell to a near-record low in recent days.
It comes as a new study shows the system is undergoing a significant "structural change".
What's next?
Experts say repeated reductions in sea ice could have global consequences.
Antarctic sea ice has again fallen to a near-record low as a new study shows the system is undergoing a significant "structural change".
Scientists have been using satellite images over the past 45 years to track the extent of sea ice on the fringe of the continent.
During that time, sea ice has fallen below 2 million square kilometres on four occasions — 2022, 2023, 2024 and 2025 — according to the Australian Antarctic Program Partnership (AAPP).
This year's data, captured on March 1, was the third-lowest annual daily minimum on record, it said.
Sea ice cover has been much more variable than it used to be, with anomalies lasting much longer than previously, the report states. (Supplied: AAD/Kym Newbery)
Will Hobbs, an AAPP sea ice researcher at the University of Tasmania, said the recent repeated lows were part of a downward trend observed since about 2016.
"What's alarming about it is how we're not alarmed anymore, because this is now the new normal,"
Dr Hobbs said.
"It's another summer with really low sea ice and that's not surprising to us anymore, because we've seen it back-to-back.
"It's just really worrying that we're seeing this long-term structural change."
Continuous satellite records of Antarctic sea ice have only been available for the past 45 years, putting limitations on research. (Supplied: AAD/Todor Iolovski)
Scientists 'reconstruct' historical record of sea ice
Dr Hobbs is part of an international research team that recently used a novel approach to ascertain the extent of Antarctic sea ice prior to satellite records.
Antarctica's icy pulse
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"Obviously, we don't have a time machine, but what we can do is do something called 'reconstructions'," he said.
Sea ice fluctuates significantly between summer and winter and is heavily affected by atmospheric conditions, including temperature, and wind speed and direction.
"Antarctic sea ice has historically been very slavish to the atmosphere," Dr Hobbs said.
"If we can reconstruct what the atmosphere looked like going back to the early 20th century, then we can probably say something about what sea ice looked like at that time."
The publication of the study coincides with the latest satellite data showing there is currently less total sea ice in Antarctica and the Arctic than previously recorded. (Supplied: AAD/Jan Lieser)
Using historical data from 30 weather stations across the Southern Hemisphere, the team was able to "reconstruct" the likely extent of Antarctic sea ice back to 1899.
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"It allows us to have a context for these extreme variabilities in Antarctic sea ice," Professor Marilyn Raphael, from the University of California in Los Angeles, said.
The results showed there was less than a 1-in-1,000 chance that the extreme minimums seen in recent years would have occurred during the 20th Century.
"The system has changed," Professor Raphael said.
"And it's changed from one where we could normally look at the [long-term] average … and have a sense of what will happen.
"We can no longer look at our average because we've tipped into a system of extremes."
Warmer ocean 'wielding an influence' on sea ice
'Five-sigma' event unfolding in Antarctica
Photo shows Iceberg in the Southern Ocean, seen from a ship.
Dr Hobbs said the recent low levels of sea ice were likely linked to warmer ocean temperatures.
"The atmosphere alone is not enough to explain what we're seeing," he said.
"The ocean has to be wielding an influence."
He said further research was needed to better understand the cause and effect of the altered conditions in the Southern Ocean.
"It's either because anthropogenic climate change has caused the ocean changes that are driving these events, or these kind of ocean events have happened in the past [prior to 1899]."
Co-authors of the sea ice reconstruction (from left) Will Hobbs, lead author Marilyn Raphael and Mark Handcock. (Supplied: AAD/Mark Horstman)
Dr Hobbs said low levels of Antarctic sea ice could have significant flow-on effects, including reduced protection of ice shelves and glaciers, which could contribute to sea level rise if they melt.
"This is potentially a global problem," he said.
The study, titled A Twenty-First Century Structural Change in Antarctica's Sea Ice System, has been published in the journal Nature Communications, Earth & Environment.