Antarctic ozone hole ranks seventh largest in 48 years, NASA and NOAA say

Sole source: The 2026 Antarctic ozone hole was the seventh largest by seasonal area in 48 years of monitoring, NASA and the National Oceanic and Atmospheric Administration (NOAA) said in their annual assessment. Its average area during the peak depletion season, from 7 September to 13 October, was about 25 million square kilometers.

The largest hole observed since monitoring began reached its maximum extent in September 2000. NASA and NOAA say the ozone layer remains on track for long-term recovery, and this year’s hole was not as deeply depleted as record holes in previous decades.

Butler on the large polar vortex

The Antarctic polar vortex creates cold conditions that allow chlorine and bromine from human-made compounds to deplete stratospheric ozone. NOAA research scientist Amy Butler said the vortex was unusually large partly because planetary-scale weather systems that usually weaken it were especially weak in August and September. That left the strongest vortex winds farther from the pole and enlarged the area with conditions favorable to ozone depletion.

Area and depth measure different things

Scientists define the hole’s area as the region where ozone falls below 220 Dobson units, a standard measure of ozone. Its largest daily area was 27.1 million square kilometers on 18 September; the seasonal average covers a longer period.

Depth describes how low ozone levels fall. NOAA instruments carried by balloons measured a minimum of 105 Dobson units over the South Pole on 17 October. The station’s record low was 92 Dobson units in October 2006. The assessment also used ground observations and satellite measurements, which have contributed to ozone monitoring since 1979. Instruments aboard NASA’s Aura, NOAA-20, NOAA-21 and the jointly operated Suomi National Polar-orbiting Partnership satellite contributed to the report.

The longer recovery

NASA and NOAA scientists say controls under the 1987 Montreal Protocol continue to drive recovery. Countries committed under the agreement to replace ozone-depleting substances with less-harmful alternatives. NOAA senior scientist Stephen Montzka said Antarctic stratospheric chlorine from those substances has fallen from its peak by about a third relative to 1980s levels.

Some of those chemicals, once used in refrigerators, air conditioners and insulation, can remain in the atmosphere or leak from old products and landfills for decades. As the compounds break down, scientists estimate that the Antarctic ozone hole will recover by the 2070s.