The Antarctic ozone hole expanded rapidly during the first half of September, reaching an estimated 25 million square kilometres on September 12, according to the Copernicus Atmosphere Monitoring Service. That measurement sat roughly 5 million square kilometres above the historical average for the period and exceeded the total land area of Antarctica.
How the Antarctic Ozone Hole Is Measured and Tracked
Scientists define the Antarctic ozone hole as any region south of 60°S where ozone column concentrations drop below 220 Dobson Units. According to the Copernicus Atmosphere Monitoring Service, researchers monitor this region throughout the Southern Hemisphere spring using multiple diagnostics alongside the physical area of the hole itself.
These supplementary metrics include the ozone-column minimum, which measures the lowest concentration inside the depleted zone, and the ozone mass deficit, which calculates the total amount of missing gas. Stratospheric temperatures also factor heavily into seasonal assessments. Laurence Rouil, Director of the Copernicus Atmosphere Monitoring Service, noted that the ozone hole’s development varies considerably from year to year based on shifting atmospheric and chemical conditions.
Cold Stratosphere Temperatures Drive Rapid September Expansion
The sharp expansion observed in mid-September coincided with a sudden drop in minimum temperatures roughly 20 kilometres above the South Pole at the 50 hectopascal level, as reported by the Copernicus Atmosphere Monitoring Service. These cold conditions allow polar stratospheric clouds to form in the lower stratosphere.
Such clouds trigger chemical reactions that activate human-made halogens like chlorine and bromine in the presence of sunlight. This process accelerates ozone destruction between August and November. The persistence of the polar vortex and stable stratospheric winds over the continent helps maintain the cold air necessary for these reactions to continue.
Comparing Recent Ozone Hole Seasons and Historical Data
The 2026 ozone hole began developing at a typical pace during the second half of August, reaching 15 million square kilometres by month’s end. That milestone arrived slightly ahead of schedule, closely tracking the 2025 season, which hit the same 15 million square kilometre threshold on August 30, according to Copernicus data.
Despite the large surface area recorded on September 12, other diagnostic markers told a different story. The ozone-column minimum and ozone mass deficit remained close to their historical averages. By comparison, the largest single ozone hole recorded in the Copernicus dataset reached 29.6 million square kilometres on September 9, 2006. Long-term monitoring by scientists using satellite and ground-based instruments since the late 1970s shows that recent years generally feature smaller and shorter-lived holes, pointing to ongoing recovery under the Montreal Protocol.
Frequently Asked Questions
What defines the Antarctic ozone hole?
The Antarctic ozone hole is classified as any area south of 60°S where total ozone column concentrations fall below 220 Dobson Units, according to the Copernicus Atmosphere Monitoring Service.
Why does the ozone hole form over Antarctica?
The hole forms because extremely cold winter and spring temperatures in the Antarctic stratosphere create polar stratospheric clouds. These clouds foster chemical reactions involving human-made halogens driven by sunlight.
Is the ozone layer recovering over the long term?
Yes. According to scientific monitoring data gathered since the late 1970s, recent years have generally seen smaller and shorter-lived ozone holes, indicating progress toward long-term recovery.
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