The ozone hole over Antarctica in September 2026 was the largest in 20 years, reaching more than 27 million square kilometers (10.4 million square miles). This was the second-largest ozone hole ever recorded for this time of year. The only larger holes occurred in 2000 and 2015, when the hole briefly expanded to over 28 million square kilometers (10.8 million square miles). This year’s hole formed earlier than usual, in August, and grew rapidly as temperatures in the stratosphere—Earth’s second layer of atmosphere—remained unusually low. The Montreal Protocol, an international agreement signed in 1987 to phase out ozone-depleting chemicals, has helped reduce these harmful substances in the stratosphere by about a third since their peak in the early 2000s. However, the 2026 ozone hole, while large in area, did not reach the same extreme levels of ozone depletion as some previous years. This means the overall loss of ozone was less severe than in past major holes. The ozone hole forms during early spring within the stratospheric polar vortex, a powerful wind system that encircles Antarctica and the Southern Ocean during winter. Extremely cold temperatures inside the vortex lead to the formation of rare polar stratospheric clouds. Chemical reactions on the particles in these clouds activate ozone-depleting gases, accelerating the destruction of the ozone layer. The size and depth of the hole depend on how isolated the air is within the vortex. A colder and stronger vortex can lead to a larger, deeper, and longer-lasting ozone hole. In recent years, atmospheric dynamics—large-scale wind and pressure patterns—have played a significant role in shaping the ozone hole. For example, changes in airflow in the months before spring can strengthen the polar vortex, leading to more severe ozone depletion. In 2026, satellite observations in May indicated that such conditions were developing, which led to predictions of a major ozone hole by September. Observations have confirmed these predictions, with the hole expected to persist through October and November unless atmospheric conditions change. Scientists are now working to quantify how much these atmospheric dynamics contributed to the severity of the 2026 ozone hole, which they expect to rank among the top 10 worst ozone hole seasons in history. The effects of the ozone hole extend beyond Antarctica, influencing weather and climate patterns across the Southern Hemisphere. A severe ozone hole can shift a climate pattern known as the Southern Annular Mode (SAM), bringing warmer, wetter conditions to New Zealand’s west coast and increased rainfall to Australia’s southeast. Conversely, when the SAM shifts in the opposite direction, it can bring more extreme wind events, such as the powerful storms that hit New Zealand in 2023. While the ozone layer is projected to fully recover by 2090, recent trends show that ozone holes are persisting longer into spring, possibly due to changing atmospheric dynamics. This means that the ozone hole will continue to influence weather and temperatures in New Zealand and other Southern Hemisphere regions for several more decades.