Antarctic Ozone Hole Ranked Seventh Largest in 48 Years as a Strong Polar Vortex Extended Depletion

The 2026 Antarctic ozone hole ranked as the seventh largest in 48 years of monitoring, NASA’s Earth Observatory reported Monday, Nov. 9. An unusually strong polar vortex created ideal conditions for depletion over a large area, the agency said. The hole was not as deep as other large holes on record, according to NASA.

Related: Human Metabolism Now Releases 2.05 Billion Tons of CO2 a Year, Up 74% Since 1985.

What the measurements showed

The peak depletion season ran from Sept. 7 to Oct. 13, NASA and the National Oceanic and Atmospheric Administration reported on Nov. 4. The hole averaged about 9.6 million square miles, or 25 million square kilometers, during that period, the agencies said. It reached its greatest one-day extent on Sept. 18, at 10.5 million square miles, or 27.1 million square kilometers.

ABC News reported that the Sept. 18 peak was about 90% as large as the record. The outlet also noted that the 2025 hole ranked as the fifth smallest since 1992.

Scientists define the hole as the area where ozone falls below 220 Dobson units, NASA said. The Dobson unit is the standard measure of ozone concentration. Balloon instruments launched from the South Pole recorded a 2026 low of 105 Dobson units directly overhead on Oct. 17, NOAA scientists found. The lowest value recorded over the South Pole was 92 Dobson units, in October 2006, according to NASA.

NASA’s two 2026 accounts name different years for the largest hole. The Nov. 4 release said the largest hole reached its maximum extent in September 2000. The Nov. 9 Earth Observatory article said the largest ozone hole occurred in 2006.

Why the hole grew

The polar vortex was unusually large in part because weather systems that usually break it up were especially weak in August and September, NOAA research scientist Amy Butler said. That weak wave activity kept the strongest vortex winds several degrees of latitude farther from the pole, Butler said. The shift created a larger area where depletion could occur, she said.

Colder conditions produce a larger hole and lower ozone values at its core, the Earth Observatory said. Year-to-year changes in area and depth come from variations in stratospheric temperature and circulation, according to NASA.

What scientists said about recovery

“The annual ozone hole has been forming later in the season in recent years, which tells us the ozone layer is healing,” said Paul Newman. Newman is a senior scientist at the University of Maryland, Baltimore County, and longtime leader of NASA’s ozone research team. He said the vortex allowed the hole to grow to proportions not seen in a decade.

Newman said the 2026 hole could have been 1 million to 2 million square miles larger if ozone-depleting substances were as prevalent as at their peak in 2000.

Chlorine levels in the Antarctic stratosphere from ozone-depleting substances have declined by about a third from their peak, relative to 1980s levels, NOAA senior scientist Stephen Montzka said.

The Montreal Protocol and the long view

The 1987 Montreal Protocol committed countries to replacing ozone-depleting substances with less harmful alternatives, NASA said. NASA and NOAA scientists said the controls in that agreement continue to drive long-term recovery of stratospheric ozone.

Chlorofluorocarbons and related compounds were once common in refrigerators, air conditioners and building insulation, according to NASA. Those chemicals can linger in the atmosphere or leach from old products and landfills for many decades, the agency said. Scientists estimate the ozone hole will recover by the 2070s, NASA and NOAA said.

The ozone layer absorbs ultraviolet light that damages DNA in plants and animals and leads to sunburn and skin cancer, according to NASA. Stratospheric ozone is distinct from ground-level ozone, which is an air pollutant, the agency said.

For more coverage, see Science and Health.

Sources

• NASA Earth Observatory: Ozone Hole Reaches Its 2026 Maximum
• NASA: NASA, NOAA Track 2026 Antarctic Ozone Hole
• ABC News via ABC7: Ozone hole in 2026 is largest in a decade, but long-term recovery remains on track

About the reporter: Theo Lin is an AI reporter covering AI, technology and science for The Boston Report. This article was produced with AI under our editorial policy. Read our AI and media disclosure.