The ozone hole is slowly shrinking. In 2025, NASA and NOAA ranked the Antarctic ozone hole as the fifth smallest since 1992, confirming that the recovery trend driven by the Montreal Protocol remains on track. Full recovery over Antarctica is projected around the late 2060s, while ozone levels at middle latitudes are rebounding faster. The hole still forms every Antarctic spring, but the long arc is bending in the right direction.
How Big the Ozone Hole Is Now
Each year, the Antarctic ozone hole peaks in late September or early October as sunlight returns to the polar stratosphere and triggers chemical reactions on ice clouds. In 2024, the hole reached its maximum single-day extent on September 28 at 22.4 million square kilometers (8.5 million square miles), making it the seventh smallest since recovery began. Ozone concentration bottomed out at 109 Dobson Units on October 5. For context, anything below 220 Dobson Units is considered “ozone hole” territory, and readings in the worst years of the 1990s and 2000s dipped below 100.
The 2025 season continued the positive trend, ranking as the fifth smallest hole on record since 1992. Year-to-year variation is normal and influenced by weather patterns and volcanic activity, so scientists focus on the multi-decade trend rather than any single season. That trend is clearly headed toward smaller, shorter-lived holes.
Why It’s Recovering
The ozone layer is healing because the chemicals that destroy it are slowly leaving the atmosphere. Chlorine- and bromine-based compounds, once widely used in refrigerants, aerosol sprays, and fire suppressants, break apart ozone molecules in the stratosphere. These substances were banned under the 1987 Montreal Protocol, but they linger for decades. As of early 2024, reactive halogen concentrations over Antarctica had dropped 28% from their peak levels. Over the mid-latitudes, where most people live, the decline is even steeper at 55%, which is enough to support a nearly normal ozone layer at those latitudes.
The chemicals haven’t disappeared entirely. Legacy equipment, old stockpiles, and slow atmospheric breakdown mean chlorine and bromine will continue cycling through the stratosphere for years. But the direction is unambiguous: less of these substances enters the atmosphere each year than breaks down, and the ozone layer thickens in response.
The Arctic Tells a Different Story
While Antarctica gets most of the attention, ozone conditions over the Arctic are far more variable. The Arctic stratosphere is warmer and more disturbed by weather systems, so it rarely develops the extreme, persistent cold needed for severe ozone loss. In March 2024, Arctic ozone concentrations hit a record monthly high, the highest in the satellite era. Strong atmospheric wave events from late December 2023 through early March pushed extra ozone into the polar stratosphere. May, June, July, and August 2024 also set new monthly records.
This stands in sharp contrast to March 2020, when the Arctic experienced unusually severe ozone depletion due to an exceptionally stable and cold polar vortex. The swing between those two extremes illustrates how much Arctic ozone depends on year-to-year weather rather than long-term chemical trends. Unlike Antarctica, the Arctic doesn’t reliably produce an ozone hole each year.
Climate Change Complicates Recovery
Greenhouse gases warm the lower atmosphere but cool the stratosphere. That cooling matters because ozone destruction happens on the surface of polar stratospheric clouds, thin ice clouds that form when stratospheric temperatures drop below minus 78°C (minus 109°F). If rising greenhouse gas levels push the stratosphere colder, these clouds could form more often or persist longer, giving ozone-depleting chemicals more opportunity to do damage even as their concentrations fall.
The Arctic is particularly vulnerable. Stratospheric temperatures there already hover just a few degrees above the cloud-formation threshold. Further cooling could tip more winters into conditions that produce significant ozone loss. Over Antarctica, temperatures are already so cold each winter that this effect is less of a game-changer, but it could delay full recovery by a few years.
The Hunga Tonga Eruption Was a Minor Factor
When the Hunga Tonga volcano erupted in January 2022 and injected a massive plume of water vapor into the stratosphere, scientists worried it might worsen ozone depletion. Water vapor can enhance the chemical reactions that destroy ozone. Modeling and satellite observations confirmed that 20% to 40% more water vapor than usual entered the Antarctic polar vortex as it formed in 2023. But the actual impact on ozone was minor, less than 4 Dobson Units.
The reason: Antarctica’s stratosphere gets so cold each winter that excess water vapor simply freezes out. The condensation process resets water vapor levels before the extra moisture can meaningfully accelerate ozone loss. This was reassuring evidence that the recovery trend can withstand natural disruptions of this kind.
When Full Recovery Is Expected
Recovery timelines differ by region. The ozone layer over the mid-latitudes (roughly between the tropics and the poles) is expected to return to 1980 levels around mid-century. The Antarctic ozone hole, where depletion has been most severe, is projected to close around the late 2060s. These projections assume continued compliance with the Montreal Protocol and its amendments.
One of those amendments, the Kigali Amendment adopted in 2016, targets hydrofluorocarbons (HFCs). These chemicals replaced the ozone-destroying compounds but turned out to be potent greenhouse gases. More than 170 countries have ratified the amendment, which requires an 80% to 85% global reduction in HFC use by 2047. Developed countries started phasing down in 2019, and most developing countries began freezing HFC use in 2024. Full implementation could prevent up to 0.5°C of global warming by 2100, making it one of the most impactful single climate actions available.
UV Radiation at Ground Level
You might expect that a recovering ozone layer would mean less ultraviolet radiation reaching the ground. In practice, the changes so far are hard to detect at most locations. Measurements of the UV index at sites like San Diego going back to 1992 show values nearly indistinguishable from reconstructed pre-depletion levels, consistent with the small ozone changes seen at subtropical latitudes. At unpolluted monitoring stations worldwide, UV trends since the mid-1990s track closely with ozone changes, but those changes have been modest outside the polar regions.
Since global ozone isn’t expected to fully return to 1980 levels until around mid-century, slightly elevated UV exposure will persist for decades. The effect is most pronounced at high southern latitudes, closer to Antarctica, where ozone depletion has been greatest.
How Scientists Track the Ozone Layer
A constellation of satellites continuously monitors ozone from space. The newest addition, NASA’s TEMPO instrument, sits in geostationary orbit 22,000 miles above the equator and provides hourly ozone measurements over North America at a resolution of 2 to 4.75 kilometers per pixel. That’s roughly twice the spatial resolution of previous instruments and a major leap from older satellites in low Earth orbit, which could only observe a given location once per day.
TEMPO is part of a growing global network. South Korea’s GEMS instrument has monitored Asia since 2020, and the European Sentinel-4 instrument launched in early 2025. Together, these geostationary satellites provide near-continuous atmospheric monitoring across most of the populated world, tracking not just ozone but nitrogen dioxide and other pollutants. Ground-based stations and balloon-borne instruments continue to provide complementary measurements, particularly over Antarctica during the annual ozone hole season.