Reaching 10.5 million square miles on September 18, 2026, the Antarctic ozone hole hit its largest one-day extent in a decade. NASA and NOAA researchers reported that an unusually powerful polar vortex prolonged ozone depletion, landing the seasonal mean area at seventh largest in 48 years of monitoring.
During the peak ozone depletion season from September 7 to October 13, 2026, the average extent of the hole covered about 9.6 million square miles, or 25 million square kilometers, according to measurements from NASA and the National Oceanic and Atmospheric Administration.
That footprint is more than twice the area of the United States. While the hole ranked seventh largest by seasonal mean area across 48 years of monitoring, it did not match the extreme depth of historical lows recorded in previous decades.
Balloon-borne instruments launched from the South Pole Baseline Atmospheric Observatory recorded a seasonal low of 105 Dobson units on October 17, 2026. That concentration is less depleted than the record-breaking low of 92 Dobson units measured in October 2006. Scientists define the ozone hole using a threshold of 220 Dobson units, a baseline derived from historic observations over Antarctica prior to 1979.
Weather Systems Drive 2026 Expansion
Researchers traced the unusual size of the 2026 hole to stratospheric dynamics rather than a resurgence of pollutants. Amy Butler, a research scientist at NOAA’s Chemical Sciences Laboratory, explained that planetary-scale weather systems originating in the lower atmosphere were especially weak in August and September. Those weak systems failed to break up the polar vortex, keeping its strongest winds farther from the South Pole.
That process created a wider expanse of ideal conditions for ozone destruction.
The polar vortex was unusually large this year in part because planetary-scale weather systems that typically well up from the lower atmosphere and break up the vortex were especially weak in August and September,
Amy Butler, research scientist at NOAA’s Chemical Sciences Laboratory
Despite the expansive area, international treaties continue to curb worse outcomes.
The 2026 ozone hole is large but could have been 1 to 2 million square miles (3.5 million square kilometers) larger if ozone-depleting substances were as prevalent in the atmosphere today as they were at their peak in 2000,
Paul Newman, a senior scientist and leader of NASA’s ozone research team
Montreal Protocol Sustains Long-Term Recovery
Measurements gathered by NASA’s Aura satellite, the NOAA-20 and NOAA-21 satellites, and the Suomi National Polar-orbiting Partnership satellite confirm that the stratospheric layer remains on track for recovery.
The annual ozone hole has been forming later in the season in recent years, which tells us the ozone layer is healing,
Paul Newman, a senior scientist and leader of NASA’s ozone research team