This year’s Antarctic ozone hole was the seventh-largest in 48 years of tracking

The 2026 Antarctic ozone hole peaked at 10.5 million square miles on Sept. 18, and NASA and NOAA ranked it the seventh largest by area in 48 years of monitoring. Paul Newman, a senior scientist at the University of Maryland, Baltimore County who has led NASA’s ozone research team at Goddard Space Flight Center, attributes the size to an unusually powerful polar vortex. Both agencies say the layer is still on course for long-term recovery.

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The hole was large but not deep. NOAA’s balloon measurements over the South Pole put the year’s lowest ozone reading at 105 Dobson units on Oct. 17, well above the record low from 2006, which is why the agencies describe the season as a larger hole without the severe thinning of the worst years. A Dobson unit measures the total amount of ozone in a vertical column of atmosphere, so a lower number means a thinner shield against solar radiation overhead.

Seventh by area: the numbers behind the ranking

NASA’s Nov. 4 release by Sally Younger of the agency’s Earth Science News Team reports that the hole’s average extent from Sept. 7 to Oct. 13 was about 9.6 million square miles, or 25 million square kilometers. The one-day maximum on Sept. 18 reached 10.5 million square miles, or 27.1 million square kilometers. Scientists define the hole as the area where total ozone falls below 220 Dobson units, a threshold NASA’s explainer on how the hole is measured describes as thin enough to qualify.

The largest hole since monitoring began peaked in September 2000. NASA’s Ozone Watch table of annual maxima lists daily peaks of 29.9 million square kilometers for 2000 and 29.6 million for 2006, with no 2026 row yet. The release does not spell out which measure the seventh-place ranking uses, so the ranking stays attributed to NASA and NOAA here. Satellite data from NASA’s Aura, NOAA-20, NOAA-21 and the jointly operated Suomi NPP contributed to the tally, and satellite monitoring has been continuous since 1979.

An unusually powerful polar vortex and weak planetary waves

NOAA research scientist Amy Butler of the Chemical Sciences Laboratory explains the weather behind the size. The vortex was unusually large because planetary-scale weather waves, which normally batter and break it up, were weak in August and September. That kept the strongest vortex winds several degrees of latitude farther from the pole, leaving a bigger area of cold air favorable for ozone destruction.

The chemistry is well established. During the dark polar winter a jet stream isolates cold air in the vortex, stratospheric clouds form, and their particles host the reactions that free chlorine and bromine from the breakdown products of ozone-depleting chemicals. When sunlight returns in spring, the chlorine destroys ozone and survives to destroy more as long as the vortex stays cold.

A shallow minimum over the South Pole and falling chlorine

The yearly low of 105 Dobson units came from NOAA’s balloon-borne instruments at the South Pole Baseline Atmospheric Observatory, part of the long record at NOAA’s South Pole ozone program. The lowest value ever recorded over the pole was 92 Dobson units in October 2006.

Newman says the hole has been forming later in the season in recent years, a sign that the layer is healing, and estimates that the 2026 hole could have been 1 to 2 million square miles larger if ozone-depleting substances were as abundant as at their 2000 peak. NOAA Global Monitoring Laboratory senior scientist Stephen Montzka reports that chlorine in the Antarctic stratosphere from these substances has dropped by about one-third from its peak.

The Montreal Protocol and the 2070s recovery date

NASA credits the Montreal Protocol of 1987 for the long-term recovery. Under that agreement, countries replaced ozone-depleting substances with less harmful alternatives. The UN Environment Programme’s ozone secretariat says the treaty was signed in 1987, entered into force in 1989, and that the ozone layer is “well on its way to recovery.” A 2016 addition, the Kigali Amendment, calls for phasing down hydrofluorocarbons, which replaced some of the older chemicals and do not deplete ozone but are potent greenhouse gases.

The chemicals do not vanish quickly. Chlorofluorocarbons were once common in refrigerators, air conditioners and insulation, and they can persist in the atmosphere or leach out of old products and landfills for decades. Scientists estimate the Antarctic hole will recover by the 2070s, the release says.

The open question for next season is how the vortex behaves. Butler’s explanation ties 2026 to weak planetary waves, a weather pattern that varies year to year, while the chlorine trend Montzka describes moves only slowly downward. A calm, wave-rich winter could yield a smaller hole even though the 2070s recovery date has not changed, and a repeat of 2026 would show whether weak wave activity in August and September is a one-season quirk. The 92-unit South Pole low of October 2006 remains the benchmark against which each year’s balloon minimum is judged.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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