Antarctic Ozone Hole Reaches Second-Largest September Size on Record, Driven by Strong Polar Vortex

Key facts

• The Antarctic ozone hole peaked at 10.6 million square miles in September 2026, the second-largest ever observed for that time of year.
• The hole began growing earlier than usual in August and by September 20 reached a size close to its October 2015 peak of 10.8 million square miles.
• The ozone hole is a patch of depleted ozone in the stratosphere over Antarctica, mainly caused by chlorofluorocarbons (CFCs) that persist for decades despite the 1987 Montreal Protocol.
• A stronger and colder polar vortex this year created conditions for the hole to grow, according to Hannah Kessenich, a physicist at the University of Otago in New Zealand.
• Kessenich told ABC News that the hole's size shouldn't cause alarm, and recovery is assessed by depth rather than area.
• Susan Solomon, an atmospheric chemist at MIT, said long-term trends show the ozone hole is slowly recovering as expected.
• A larger ozone hole shifts the Southern Annular Mode into a positive phase, causing increased rainfall on Australia's southeast coast.
• A 2023 study in Nature found that particles in wildfire smoke spark chemical reactions that break down ozone.