Antarctic Sea Ice 2026: Third-Lowest Maximum on Record

Copernicus says Antarctic sea ice peaked at 18.19 million square kilometers on September 10, 2026, the third lowest on record.

Antarctic sea ice reached its yearly maximum of 18.19 million square kilometers on September 10, 2026, the third lowest in the 48-year satellite record, according to the Copernicus Climate Change Service. The UK Met Office reports a September average of 17.76 million square kilometers, also third lowest. This article on Antarctic sea ice 2026 compares the two reports and explains why Antarctic sea ice behaves differently from Arctic ice.

What did Copernicus report?

In its September 2026 bulletin, published October 14, Copernicus said the Antarctic annual maximum was 18.19 million square kilometers on September 10, the third lowest in the 48-year record. The September monthly extent was 1.2 million square kilometers, or 6.3%, below average, and the third lowest for the month. The page does not say which years had lower maxima, so we do not name them here. Our article on the Arctic sea ice minimum covers the opposite pole.

What did the Met Office report?

The Met Office, using the OSI SAF Sea Ice Index, gave a September 2026 Antarctic extent of 17.76 million square kilometers, the third lowest September on record after 2023 and 2024. That is 1.08 million square kilometers below the 1981 to 2010 average. The Met Office also reports a trend of minus 0.08 million square kilometers per decade across the satellite record since 1979, and calls it weakly negative. The page does not give the seasonal maximum or its rank.

Why do the two reports differ?

Copernicus reports a single-day annual maximum, while the Met Office reports a monthly September average. A daily peak is higher than a monthly mean for the same season. The two also use different reference periods and sea ice products, so the deficits differ: 1.2 million below the Copernicus average and 1.08 million below the Met Office 1981 to 2010 average. This explanation is general and is not stated in either source. Both agree on the main finding that the extent was the third lowest.

How is the Antarctic different from the Arctic?

The Arctic is an ocean surrounded by land, while Antarctica is a continent surrounded by ocean. Sea ice around Antarctica can spread widely in winter and mostly melts each summer, while Arctic ice is more confined. The Met Office describes the long-run Antarctic trend as weakly negative, in contrast to the larger declines in the Arctic. These geographic contrasts are general knowledge and are not drawn from the two pages. A weak long-term trend does not mean recent years are normal, because the last few years have included very low values.

What do rankings like third lowest mean?

A rank compares one year with all years in a record. A third-lowest value means two years had lower values. Copernicus counts 48 years in its record, so the 2026 maximum was in the lowest 6.3% of years, which is our own arithmetic (3 divided by 48). A rank does not show how large the gap is between years, so the extent values matter too. The gap between the 2026 monthly extent and the average is 6.3% in the Copernicus figure.

How does ice around Antarctica connect to the wider climate?

Sea ice affects how much sunlight the ocean reflects and how heat moves between the ocean and atmosphere. That is a general principle and not a finding from either source. For related Antarctic science, our article on the Antarctic ozone hole in 2025 covers a separate atmospheric measure, and our article on glacier loss covers land ice. Sea ice floating on the ocean does not raise sea level when it melts, while land ice does, which our article on sea level rise explains.

What do recent years show?

The Met Office places September 2026 third lowest after 2023 and 2024, so the two lowest Septembers in its ranking are both recent. Copernicus likewise describes the 2026 maximum as the third lowest in 48 years. Together the reports suggest that low Antarctic sea ice has not been a one-off in this period. The pages do not say whether this marks a lasting change, and the Met Office still describes the full-record trend as weakly negative. Scientists continue to study the reasons, and the sources we used do not offer a cause, so we do not suggest one.

How to read the numbers

Three habits help. Check whether a value is a daily peak or a monthly average. Check the baseline used for the average. Check which dataset produced the rank. With these checks, 18.19 million, 17.76 million and 1.2 million or 1.08 million below average all fit one picture. By our own arithmetic, the difference between the two extent values is 0.43 million square kilometers, which comes from the daily-versus-monthly distinction and the different products.

Glossary

Annual maximum: the highest sea ice extent reached during the year
Monthly extent: the average extent over a month
Baseline: the reference years used to compute an average
Sea Ice Index: a dataset that tracks sea ice extent over time
Weakly negative trend: a slight decline over the record

These definitions are general explanations and are not quoted from the sources.

What is not covered here?

Neither page gives the sea ice thickness, the regional pattern of the loss around Antarctica or the causes of the low extent. We have not guessed at them. Readers who want those details should consult the full Copernicus and Met Office reports.

Key facts at a glance

Annual maximum: 18.19 million square kilometers on September 10, 2026 (Copernicus)
Rank: third lowest in 48 years
September average: 17.76 million square kilometers (Met Office)
Deficit: 1.08 million square kilometers below the 1981 to 2010 average
Long-term trend: minus 0.08 million square kilometers per decade

Frequently asked questions

How big was the 2026 Antarctic sea ice maximum?

18.19 million square kilometers on September 10, according to Copernicus.

Was it a record low?

No. It was the third lowest in the 48-year record.

Why do two agencies give different numbers?

One reports a daily peak and the other a monthly average, and they use different products.

Does melting sea ice raise sea level?

Floating sea ice does not, in general, while melting land ice does.