The ozone hole over Antarctica expanded to 27.1 million square kilometres in 2026, its largest recorded extent in ten years. Unusual weather conditions, rather than rising pollution levels, were largely responsible.
Like clockwork, the ozone hole appeared over Antarctica again this year. But its size has drawn particular attention: according to measurements by NASA and the US National Oceanic and Atmospheric Administration (NOAA), the ozone hole reached a maximum area of 27.1 million square kilometres on 18 September 2026. That is roughly three times the size of the United States and equivalent to 90 per cent of the all-time record, set on 9 September 2000.
Contrary to what might be expected, pollution played a relatively minor role in this year’s expansion. Scientists attribute much of the increase to unusual weather conditions, particularly an exceptionally strong polar vortex — a large area of low pressure and cold air circulating clockwise around the South Pole.
The unusually powerful vortex helped create polar stratospheric clouds, providing favourable conditions for ozone destruction. At the same time, weather systems that would normally help limit the hole’s expansion were weaker than usual, allowing it to grow more extensively.
The increase is significant compared with last year. On 9 September 2025, the ozone hole reached a maximum area of 22.86 million square kilometres, making it the fifth smallest recorded since 1992.
Nevertheless, scientists say the latest figures are not necessarily cause for alarm. They remain optimistic that the ozone layer could recover by the end of this century. Paul Newman, a senior researcher at the University of Maryland, points out that the ozone hole has been forming progressively later in recent years, suggesting that the layer is gradually healing.
A larger ozone hole does not mean the recovery has stalled
Ozone depletion generally begins between the end of winter and the start of spring in the Southern Hemisphere. The process is triggered by human-made gases containing chlorine and bromine, particularly chlorofluorocarbons (CFCs), which were widely used in solvents and various types of foam.
Carried into the Antarctic stratosphere by cold air currents, these gases are broken down by ultraviolet radiation, releasing chlorine and bromine atoms. These then interact with particles in stratospheric clouds, triggering chemical reactions that progressively destroy ozone molecules.
Despite this process, international efforts have significantly reduced the concentration of ozone-depleting substances. According to Stephen Montzka, a senior scientist at NOAA’s Global Monitoring Laboratory, chlorine levels in the Antarctic stratosphere have fallen by approximately 30 per cent since 1985. Much of that progress is attributed to the Montreal Protocol, adopted by the international community in 1987, two years after the ozone hole was first identified.
NASA and NOAA continue to monitor the health of the ozone layer through a combination of satellites, weather balloons and ground-based instruments that measure ozone concentrations.
Newman estimates that this year’s ozone hole could have been between 2.5 million and 5.2 million square kilometres larger if atmospheric pollutants responsible for ozone depletion had remained at levels comparable to those recorded in 2000.
The unusual figures for 2026 serve as a reminder that environmental recovery is rarely a straightforward process. While the long-term trend remains encouraging, scientists stress the importance of continuing to eliminate or reduce chemicals that contribute to ozone depletion.
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