Dangerous ozone hole widened by polar vortex in 2026, Boulder researchers say

An unusually large polar vortex in the Antarctic winter pushed the dangerous “ozone hole” in the atmosphere to its seventh-largest measurement in nearly a half-century of monitoring, according to the Boulder-based scientists who co-lead the annual tests. 

The hole in the protective ozone layer peaked at 10.5 million square miles Sept. 18, and averaged 9.6 million square miles during the peak month from early September to early October, according to the National Oceanic and Atmospheric Administration. The largest single-day reading since tests began in 1979 was 11.5 million square miles in September 2000.

Atmospheric ozone is a good thing, protecting life on Earth from damaging ultraviolet rays, while ground level ozone is a bad thing for human health, with nine Colorado Front Range counties routinely violating U.S. standards for the lung-damaging gas. International scientists have been working to restore atmospheric ozone for decades, since research discovered refrigerants and other human-made aerosols rose into the atmosphere and eroded the protective layer. 

The “good” ozone layer continues to heal over time, despite weather-caused expansions of the Antarctic hole in some years. A spike in 2023 was due in part to a South Pacific underwater volcano eruption that spewed hot water vapor into the heavens. The peak day that September was 10 million square miles, and the hole averaged 8.9 million square miles for the peak month. That’s roughly the size of North America. 

Depleted atmospheric ozone leads to sunburns, more cases of skin cancer, and damaged DNA in humans and animals, as well as eye damage. 

“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, a Maryland-based senior scientist at NASA’s ozone research team at the Goddard Space Flight Center. “But an unusually powerful polar vortex has extended ozone depletion in the Antarctic this season, allowing the hole to grow to proportions we haven’t seen in a decade.” 

One NOAA researcher said, “Planetary-scale weather systems that typically well up from the lower atmosphere and break up the vortex were especially weak in August and September.” 

Ozone research is co-led by a NOAA Global Monitoring Lab in Boulder. Some Boulder-based senior scientists and lab technicians spend the winter at the Amundsen-Scott South Pole Station launching balloon-carried “ozonesondes.” The instruments are able to take direct ozone readings as they travel up through different layers of the atmosphere. The ozonesonde on the American balloons was invented in Boulder in the 1960s, and is still manufactured by Boulder companies.

It’s true that weather or atmospheric anomalies like a volcanic eruption have pushed the ozone hole wider a few times in recent years, said Boulder-based NOAA senior scientist Stephen Montzka, in an email response to questions. 

“Despite the variability in weather and ozone depletion that we see, the long-term trend is that the ozone hole is slowly recovering, and this is the result of substantial declines in the concentrations of ozone-depleting gases. Unfortunately, those gases get removed from the atmosphere only very slowly over time, through natural removal processes, so recovery is taking a long time,” he said. 

While varied, progress will continue measurably if nations keep complying with past phase-out agreements for the damaging chemicals, Montzka added. International agreements cut the use of the most damaging chemicals in aerosols, refrigeration and propellants for foam and other materials. 

“Once the atmospheric concentrations of these gases drop below a certain point, ozone holes will no longer be seen, even with variations in weather that happen from year-to-year,” he said.