The World Meteorological Organization's 2026 Scientific Assessment of Ozone Depletion, released in May 2026, confirms that the stratospheric ozone layer continues its slow but measurable recovery. The assessment, produced every four years by hundreds of scientists across 40 countries, concludes the ozone layer is on track to return to 1980 benchmark levels by 2066 over most of the globe, and by 2045 over mid-latitudes.
Ozone Layer Recovery Timeline | 2026 WMO Projections
The 2026 assessment updates the projections from the 2022 report with four additional years of satellite and ground-based measurement data. Key recovery timelines confirmed in the report:
- Mid-latitudes (45N to 45S): Full recovery to 1980 levels projected by 2045, unchanged from the 2022 estimate.
- Northern Hemisphere polar region: Recovery projected by 2045.
- Southern Hemisphere polar region: Recovery projected by 2066, five years earlier than the 2022 estimate of 2071, due to faster-than-expected decline in atmospheric chlorine levels.
- Antarctic ozone hole: Expected to close permanently by 2066.
Dr. Yamide Dagnet, WMO Deputy Secretary-General, stated at the report's press briefing in Geneva: "The Montreal Protocol is working exactly as designed. The chlorine and bromine levels that caused the hole are declining at a rate consistent with our models. The trajectory is clear."
Montreal Protocol | Why It Worked
The 1987 Montreal Protocol on Substances that Deplete the Ozone Layer remains the only United Nations treaty ever ratified by all 198 UN member states. It phased out the production and consumption of chlorofluorocarbons (CFCs), halons, and hydrochlorofluorocarbons (HCFCs) that were responsible for stratospheric ozone destruction. The 2026 assessment attributes approximately 99% of controlled substances to the Protocol, with compliance rates above 97% across all major signatory nations in 2025.
The Kigali Amendment, which entered into force in 2019, extended the Protocol's scope to include hydrofluorocarbons (HFCs). HFCs do not deplete ozone but are potent greenhouse gases. The 2026 assessment estimates the Kigali Amendment will avoid 0.3 to 0.5 degrees Celsius of global warming by 2100, a co-benefit the Protocol's drafters did not anticipate in 1987.
Antarctic Ozone Hole | 2025 Measurements
The 2025 Antarctic ozone hole season, observed from August through December, was the fifth-smallest on record in terms of peak area. The hole reached a maximum extent of 23.1 million square kilometers on September 17, 2025, compared to the 1990s average peak of 24.8 million square kilometers. The European Space Agency's Sentinel-5P satellite, launched in 2017, provided the highest-resolution daily mapping of the hole to date, with a 3.5-kilometer ground resolution that resolves boundary structures invisible to earlier instruments.
Importantly, the 2026 report notes that year-to-year variability in hole size is dominated by polar vortex dynamics and temperature fluctuations in the stratosphere, not by changes in ozone-depleting substance concentrations. This means a large hole in any given year does not indicate a reversal of the recovery trend. The underlying chemical trend is firmly downward.
Emerging Threats | Wildfire Smoke and Volcanic Aerosols
The 2026 assessment raises two new concerns that were not prominent in earlier reports. First, smoke aerosols from the extreme wildfire seasons of 2020 and 2023 were detected at stratospheric altitudes, where they can catalyze ozone-destroying reactions. Scientists at the National Oceanic and Atmospheric Administration measured smoke particles at 20 kilometers altitude following the 2023 Canadian wildfires, the first time such an injection had been directly measured. The report notes the effect is temporary but calls for more monitoring data before the magnitude can be quantified in recovery models.
Second, the January 2022 Hunga Tonga-Hunga Ha'apai eruption injected an estimated 146 teragrams of water vapor into the stratosphere, producing an unprecedented moistening of the middle atmosphere. Increased stratospheric water vapor accelerates heterogeneous ozone-destroying reactions. NOAA's Global Monitoring Laboratory reported a 2 to 3 percent decrease in column ozone over the Southern Hemisphere mid-latitudes in 2022 and 2023, attributed in part to the Tonga water vapor injection. By 2025, column ozone had returned to pre-eruption levels.
Why This Matters
The ozone layer absorbs 97 to 99 percent of the Sun's medium-frequency ultraviolet light. Without it, UV-B radiation at the surface would increase dramatically, raising skin cancer incidence, suppressing immune function in humans and animals, and reducing marine phytoplankton productivity, which underpins the oceanic food chain and accounts for roughly half of Earth's oxygen production. The Montreal Protocol's success is the clearest proof of concept humanity has for coordinated global environmental action.
Frequently Asked Questions
- Is the ozone layer healing? Yes. The 2026 WMO assessment confirms measurable recovery. The ozone layer is projected to reach 1980 levels by 2045 at mid-latitudes and by 2066 at the poles.
- What caused the ozone hole? Chlorofluorocarbons (CFCs) and halons released primarily by refrigerants and aerosol propellants from the 1950s through the 1990s. The Montreal Protocol banned these substances.
- How is ozone measured? By a network of ground-based Dobson spectrophotometers, ozonesonde balloon flights, and satellite instruments including NASA's Aura MLS and ESA's Sentinel-5P.
- Can wildfires reverse ozone recovery? The 2026 assessment says wildfire smoke aerosols can cause temporary, localized ozone reductions but are not expected to reverse the long-term recovery trend. More monitoring data is needed.