The Antarctic ozone hole expanded rapidly during the first half of September, reaching an estimated 25 million square kilometers on September 12, according to the Copernicus Atmosphere Monitoring Service (CAMS). This measurement placed the ozone hole roughly 5 million square kilometers above the historical average for that period. The rapid expansion occurred ahead of the United Nations International Day for the Preservation of the Ozone Layer on September 16, as reported by sustainabilityonline.net.
Antarctic Ozone Hole Reaches 25 Million Square Kilometers
Observations showed that the ozone hole had been developing at a typical rate through August, reaching the 15 million square kilometers threshold by the end of the month, which was similar to the timing seen during the 2025 season. However, unlike the previous year, the area remained above average as the Antarctic spring progressed. The sharp increase in mid-September coincided with a sudden decrease in minimum temperatures approximately 20 kilometers above the South Pole, according to Down To Earth.
Atmospheric Factors and Seasonal Development
The seasonal ozone depletion process in the Southern Hemisphere stratosphere is driven by cold winter temperatures that allow the formation of polar stratospheric clouds. These clouds activate halogens in the presence of sunlight, enabling the rapid destruction of ozone between August and November. The Antarctic region is particularly susceptible to these formations because its polar vortex and stratospheric winds provide stable conditions that allow cold air to persist over the continent.
Despite the larger-than-average geographic area, other key diagnostic indicators tracked by scientists remained close to historical averages. According to CAMS data, the ozone-column minimum—which measures the lowest ozone concentration within the defined hole—and the ozone mass deficit remained near their typical values. Lawrence Rouil, Director of CAMS, noted that the event demonstrates how developments can vary considerably from year to year depending on atmospheric and chemical factors. While we have seen its area increase rapidly in early September this year, other indicators remain close to historical averages,
Rouil stated, adding that CAMS provides the high-quality data, forecasts and analyses needed to understand the state of the ozone layer and track its long-term recovery.
Long-Term Recovery and Historical Context
Scientists have monitored the Antarctic ozone hole using ground-based and satellite observations since the late 1970s. The largest recorded area in the CAMS dataset reached 29.6 million square kilometers on September 9, 2006. In broader assessments, organizations such as the World Meteorological Organization (WMO) have noted that recent years have generally seen smaller and shorter-lived ozone holes, reflecting progress toward the long-term healing of the atmosphere.
These variations occur within a broader trend toward recovery supported by the Montreal Protocol on Substances that Deplete the Ozone Layer, which phased out chemicals such as chlorofluorocarbons once widely used in refrigeration and fire-fighting foam. Continued monitoring by networks such as the WMO Global Atmosphere Watch and CAMS remains essential for tracking annual fluctuations against the background of long-term ozone layer recovery.