Countries are doing the right thing by continuing to ban chemicals called CFCs and HCFCs, which deplete the ozone layer above Earth. However, while this helps restore the protective ozone layer, scientists have found that restoring the ozone layer will lead to greater global warming than originally thought. Air pollution from vehicles, factories, and power plants also degrades the ozone layer near the Earth’s surface, causing health problems and warming the planet.
The Antarctic ozone hole formed in 2025 closed on December 1, 2025, marking the earliest closure since 2019. The 2025 ozone hole was also relatively small for the second year in a row compared to the large and long-lasting ozone holes of 2020–2023, and its ozone concentrations were higher, raising hopes for ozone layer recovery.
According to the Copernicus Atmosphere Monitoring Service, some unusual features of the 2025 ozone hole compared to previous years were higher-than-normal minimum ozone column values and lower-than-normal ozone mass deficit values.
The extent of the ozone hole and its duration since 2020 are still under investigation, but it is generally accepted that it is related to exceptional atmospheric conditions, including the massive eruption of Hunga Tonga Volcano in 2022, which released large amounts of ash and water vapor into the stratosphere, playing a role in major atmospheric pollution.
CAMS / ECMWF
The ozone hole over Antarctica exhibits pronounced seasonal cycles, forming annually in the Southern Hemisphere spring (September-December) when the cold polar vortex activates ozone-depleting chemical reactions. It “opens” and “closes” during these months, but has been shrinking and closing earlier in recent years thanks to international efforts to ban ozone-depleting substances, foreshadowing a full recovery by the mid-21st century.
Formation and Closure Cycle:
Emergence (August-September): After the polar winter, a cold, isolated polar vortex forms over Antarctica. Sunlight returns, triggering chemical reactions involving chlorine and bromine (from CFCs) on the surface of the polar stratospheric clouds, leading to rapid ozone depletion.
Peak (September-October): The hole reaches its maximum size and depth.
Closure (November-December): As the Southern Hemisphere warms, the polar vortex weakens and collapses, ending conditions for active ozone destruction, and the hole “heals.”
The WMO Ozone Bulletin reports that the low level of ozone depletion observed in 2024 was partly due to natural atmospheric factors that cause interannual variations. However, the long-term positive trend reflects the success of concerted international action.
The WMO Ozone Bulletin was released to mark the International Day for the Preservation of the Ozone Layer on 16 September 2025 and the 40th anniversary of the Vienna Convention, which recognized stratospheric ozone depletion as a global problem and laid the foundation for mobilizing international cooperation in ozone layer research, systematic observations and scientific assessments.
To date, the Montreal Protocol has led to the phase-out of over 99% of the production and consumption of controlled ozone-depleting substances used in refrigeration, air conditioning, firefighting foam, and even hairspray. As a result, the ozone layer will recover to 1980s levels by the middle of this century, significantly reducing the risk of skin cancer, cataracts, and ecosystem damage due to excessive UV exposure.
Pixabay
According to the WMO Bulletin, the total amount of stratospheric ozone in 2024 was higher than in previous years over most of the globe. The depth of the Antarctic ozone hole in 2024, which appears over Antarctica every spring, was lower than the 1990–2020 average, and the maximum ozone mass deficit (MMD) on September 29 was 46.1 million tonnes. This is smaller than the relatively large holes observed between 2020 and 2023.
The ozone hole in 2024 developed relatively slowly, with a slow depletion of the ozone layer observed throughout September, followed by a relatively rapid recovery after reaching its maximum deficit. This persistent, later appearance was identified as a reliable sign of the initial recovery of the Antarctic ozone hole, the Bulletin reports.
NASA and NOAA have estimated the 2025 ozone hole to be the fifth-largest since 1992. Despite its continental scale, the ozone hole over Antarctica in 2025 was small compared to previous years and is likely to recover by the end of this century, according to NASA and the National Oceanic and Atmospheric Administration (NOAA). This year’s ozone hole was the fifth-largest since 1992, when the historic international agreement to phase out ozone-depleting substances took effect.
At the peak of this year’s ozone depletion season, from September 7 to October 13, the average ozone hole area was approximately 18.71 million square kilometers (7.23 million square miles). The 2025 ozone hole has already begun to disappear, almost three weeks earlier than usual over the past decade.
On September 9, the hole reached its largest single-day size of the year, measuring 8.83 million square miles (22.86 million square kilometers). It was about 30% smaller than the largest hole ever observed in 2006, with an average area of 10.27 million square miles (26.6 million square kilometers).
“As predicted, we’re seeing a trend toward smaller ozone holes compared to the early 2000s,” said Paul Newman, a senior scientist at the University of Maryland, Baltimore County, and the leader of the ozone research team at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “They’re forming later in the season and decaying earlier. But we still have a long way to go before they recover to 1980s levels.”
Monitoring conducted this year has shown that ozone-depleting chemical controls established by the Montreal Protocol and subsequent amendments are promoting a gradual recovery of the stratospheric ozone layer, which is likely to be fully restored by the end of this century, according to scientists from NASA and NOAA.
The ozone layer acts as a planetary sunscreen, helping protect life from the sun’s harmful ultraviolet (UV) radiation. It is located in the stratosphere, which ranges from 11 to 50 kilometers above the Earth’s surface. A depleted ozone layer allows more UV rays to reach the surface, causing crop damage and increasing the incidence of skin cancer and cataracts, among other negative health effects.
The process of ozone depletion begins when artificial compounds containing chlorine and bromine rise high into the stratosphere, many miles above the Earth’s surface. Freed from their molecular bonds by intense ultraviolet radiation, the chlorine and bromine molecules then react to destroy ozone molecules. Chlorofluorocarbons and other ozone-depleting compounds were previously widely used in aerosol sprays, foams, air conditioners, and refrigerators. The chlorine and bromine in these compounds can persist in the atmosphere for decades, even centuries.
“Since peaking around 2000, levels of ozone-depleting substances in the Antarctic stratosphere have decreased by about a third compared to pre-ozone hole levels,” said Steven Montska, a senior scientist at NOAA’s Global Monitoring Laboratory.
NOAA scientists launch a weather balloon carrying an ozone probe near the South Pole in September 2025. Simeon Bash/IceCube/NOAA
Under the 1987 Montreal Protocol, countries agreed to replace ozone-depleting substances with less harmful alternatives.
“The hole would be a million square miles larger this year if there was the same amount of chlorine left in the stratosphere as there was 25 years ago,” Newman said.
However, now-banned chemicals persist in old products, such as building insulation, and in landfills. As emissions from these outdated methods decline over time, projections indicate that the Antarctic ozone hole will recover by the late 2060s.
Previously, NASA and NOAA estimated the depth of the ozone hole using a time interval dating back to 1979, when scientists began monitoring ozone levels in Antarctica using satellites. According to these data, the ozone hole’s area this year was the 14th smallest in 46 years of observations.
Factors such as temperature, weather, and the strength of the winds that wash over Antarctica, known as the polar vortex, also influence ozone levels from year to year. A weaker-than-normal polar vortex this August contributed to above-normal temperatures and likely contributed to the shrinking of the ozone hole, according to Laura Chiasto, a meteorologist at NOAA’s Climate Prediction Center.
This map shows the size and shape of the ozone hole over the South Pole on the day of its maximum extent in 2025. Moderate ozone loss (orange) is visible against a backdrop of areas of more intense ozone loss (red). Scientists describe the ozone “hole” as an area in which ozone concentrations fall below the historical threshold of 220 Dobson units. Photo by Lauren Dauphin, NASA Earth Observatory. This image uses NASA Ozone Watch and GEOS-5 data from the NASA Global Modeling and Assimilation Facility (GSFC) Office of Global Climate Change (GMC).
Researchers monitor the ozone layer around the world using instruments on NASA’s Aura satellite, the NOAA-20 and NOAA-21 satellites, and the Suomi National Polar-Orbiting Partnership satellite, jointly operated by NASA and NOAA.
NOAA scientists also use instruments mounted on weather balloons and upward-facing instruments to measure stratospheric ozone directly above the South Pole Atmospheric Baseline Observatory. Data from the balloons showed that ozone concentrations reached their lowest point of 147 Dobson Units on October 6 of this year. The lowest value ever recorded over the South Pole was 92 Dobson Units in October 2006.
A Dobson unit is a unit of measurement indicating the total number of ozone molecules in the atmosphere above a given point. A value of 100 Dobson units corresponds to a layer of pure ozone 1 millimeter thick (approximately the thickness of a dime) under standard temperature and pressure conditions.
On the other hand, researchers believe the ozone layer amplifies global warming. As the ozone layer recovers, global warming also intensifies. Researchers predict that by 2050, ozone will be second only to carbon dioxide as a warming factor, negating many of the benefits of banning chlorofluorocarbons (CFCs). While this gas protects life on Earth from dangerous ultraviolet radiation, the portion of it located near the Earth’s surface acts as a greenhouse gas, trapping heat in the atmosphere.
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Banning the use of ozone-depleting chemicals, such as CFCs, has allowed the protective layer to gradually recover. However, researchers warn that, combined with increased air pollution, ozone could cause 40% more warming than previously estimated.
Countries are doing the right thing by continuing to ban chemicals called CFCs and HCFCs, which deplete the ozone layer above Earth. However, while this helps restore the protective ozone layer, scientists have found that restoring the ozone layer will lead to greater global warming than originally thought. Air pollution from vehicles, factories, and power plants also degrades the ozone layer near the Earth’s surface, causing health problems and warming the planet.
A study published in the journal Atmospheric Chemistry and Physics used computer models to simulate how the atmosphere will change by mid-century. The models assumed a scenario with low levels of air pollution control, but with the gradual phase-out of CFCs and HCFCs, as required by the Montreal Protocol. The results show that phasing out CFC and HCFC production, primarily to protect the ozone layer, is having less of a climate benefit than previously thought. CFCs and HCFCs are greenhouse gases that warm the planet. Countries banned them to preserve the ozone layer, expecting this to also help combat climate change. But as the ozone layer recovers, this leads to even greater warming. Countries that reduce air pollution partially limit the formation of the ozone layer at the earth’s surface. However, the ozone layer will continue to recover for decades, regardless of air quality policies, inevitably leading to warming.
Protecting the ozone layer remains crucial for human health and skin cancer prevention. The ozone layer protects the Earth from dangerous ultraviolet radiation, which can harm people, animals, and plants. However, research shows that climate policy needs to be updated to account for the more significant warming effects caused by ozone exposure.
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