Storyboard: Antarctic Sea Ice
What is sea ice?
Sea ice is the floating layer of ice 1-2 m thick that forms on the surface of the ocean around Antarctica (and the Arctic).
Sea ice can either float freely or be connected to land. Free-floating sea ice is made up of ice floes of different sizes, usually covered with snow, and often broken up by cracks, open-water leads, and polynyas.
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Why does Antarctic sea ice matter?
With its vast ice cover, Antarctica acts as the planet’s air-conditioner, helping to regulate the temperature difference between the equator and the poles. This, in turn, influences large-scale atmospheric and oceanic circulation, shaping global climate patterns.
Sea ice also serves as an important habitat for plants and animals that are vital for local ecosystems and fisheries.
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The seasonal cycle of Antarctic sea ice
Antarctic sea ice waxes and wanes, increasing in area sixfold between summer (December-February, minimum extent) and winter (June-August, maximum extent).
Figures from NSIDC (top) and Zack Labe (bottom)
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The role of albedo in Antarctic warming
Albedo is the measure of how much sunlight a surface reflects. Bright surfaces, such as snow, reflect up to 90% of sunlight, whereas darker surfaces, like ocean water, reflect less than 10%.
Sunlight absorption warms the surface, causing sea ice and snow to melt, which reduces reflectivity and accelerates further melting.
If this highly reflective Antarctic sea ice were to dissapear, it could significantly warm Antarctica.
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Recent declines in Antarctic sea ice: a historical perspective
Until 2015, Antarctic sea ice showed little year-to-year variation, and was even slightly increasing.
But since 2015, sea ice concentrations have dramatically fallen, breaking records in 2017, 2022 and then again in 2023.
However, satellite records have been available only since 1979, a relatively short period for long-term monitoring. This has led scientists to question how unusual these record-breaking low years truly are.
According to a long-term reconstruction of the 20th century (see Figure), sea ice extent in recent years has been unusually low.
Figure from NOAA
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2023: a crazy year
2023 was a very unusual year. Maximum sea ice extent was over 2 million square kilometres lower than average.
In fact, in July 2023, the area of sea ice “missing” was equivalent to the size of the world’s tenth-largest country.
You can see from the Figure that sea ice extent in winter (JJA) 2023 was very much lower than any other year in the satellite record.
Sea ice in 2024 and 2025 has also remained low, although not as low as in 2023
Figure from Gilbert & Holmes (2024)
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What happened in 2023?
Watch the full video here
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Regime shift?
The recent years of lower sea ice and several record-breaking years have led scientists to speculate that Antarctic sea ice may have entered a new regime, with low sea ice becoming the new norm.
Watch the full video here
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Takeaways
- Antarctic sea ice is a critical part of the polar climate system which regulates the weather and climate of the planet as a whole.
- Antarctic sea ice acts as the planet’s “air-conditioner” because of its albedo.
- Realistically representing Antarctic sea ice albedo is crucial for accurate climate and ocean model predictions. But while models perform well on average and over large areas, they struggle to capture the full spatial and temporal variability of albedo.
- Sea ice varies hugely throughout the year, with large changes between the summer minimum and winter maximum.
- Long-term sea ice trends remained relatively stable until 2015. Since then, Antarctic sea ice concentrations have fallen dramatically, potentially entering a new regime.
- For further reading, see these PolarRES papers:
- Gilbert & Holmes (2024): Read here
- Verro et al. (preprint): Coming soon!
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