NASA's Earth Observatory reported Monday, November 9, that the Antarctic ozone hole in 2026 ranked seventh largest by seasonal average area in 48 years of monitoring. Its average extent from September 7 to October 13 was about 25 million square kilometers, according to measurements released by NASA and the US National Oceanic and Atmospheric Administration. Scientists said the unusually large area did not mean the protective ozone layer had stopped its long-term recovery.
The ozone layer in the stratosphere absorbs ultraviolet radiation that can damage living tissue. Researchers define the ozone hole as the region where ozone falls below 220 Dobson units, a measure of the amount of gas above a given area. NASA emphasized that the term does not mean the atmosphere there contains no ozone. Scientists first identified severe seasonal thinning over Antarctica in the 1980s.
The hole reached its greatest area on September 18, at about 27.1 million square kilometers, NOAA said. That was roughly 90% of the largest daily area observed in 2000. Measurements from instruments at the South Pole put the lowest overhead concentration this year at 105 Dobson units on October 17. NASA said the 2026 hole was broad but less deep than some other large holes.
NASA and NOAA attributed the unusually wide depletion mainly to a strong Antarctic polar vortex. NOAA scientist Amy Butler said weak large-scale atmospheric disturbances in August and September allowed the vortex to remain strong across a wider area. Its cold, isolated air supports the cloud chemistry that enables chlorine and bromine from human-made chemicals to destroy ozone. Satellite observations and ground instruments provide complementary measurements.
The agencies said restrictions under the 1987 Montreal Protocol have reduced ozone-depleting chemicals despite this year's large hole. NOAA reported that chlorine levels in the Antarctic stratosphere from those substances have fallen by about one third from their 1980s levels. NASA said annual changes in weather can still make a single year's hole much larger or smaller, so its area alone is not a measure of whether recovery has reversed.
NASA's new analysis places the 2026 measurements in a satellite record extending back to 1979. The agencies expect Antarctic ozone to return to roughly 1980 levels in the 2070s as long-lived chemicals continue to decline. They will keep using satellites, balloons and ground instruments to distinguish short-term atmospheric swings from the slower recovery trend.
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