The hole in the ozone layer over Antarctica is one of the few global environmental problems with a documented path toward repair. The World Meteorological Organization (WMO) reported in December 2025 that the 2025 Antarctic ozone hole was small and short-lived, which it said confirms the long-term recovery trend. This article explains what the numbers show, why they matter, and what they do not yet prove.
What is the ozone layer?
The ozone layer is a region of the stratosphere with a relatively high concentration of ozone, a molecule made of three oxygen atoms. In general terms, it absorbs much of the Sun’s ultraviolet radiation before it reaches the ground. An ozone hole is a seasonal thinning of that layer over a polar region, and the Antarctic hole forms each Southern Hemisphere spring. Each season is shaped by stratospheric temperatures and winds over the Southern Hemisphere, and by the ozone-depleting substances (ODS) that humans have emitted.
How big was the 2025 ozone hole?
NASA and NOAA ranked the 2025 hole as the fifth smallest since 1992, the year the Montreal Protocol took effect. The average extent during the peak depletion period, from September 7 to October 13, was about 7.23 million square miles (18.71 million square kilometers). That is roughly 30 percent smaller than the largest hole ever observed, in 2006.
- Early breakup: NASA and NOAA found the hole was breaking up nearly three weeks earlier than the average of the past decade
- Closure: the Copernicus Atmosphere Monitoring Service (CAMS) said the hole closed on December 1, the earliest closure since 2019
- Comparison: CAMS described it as the smallest hole in five years
Why does one small year not settle the question?
NASA and NOAA note that atmospheric dynamics cause year-to-year variability. A cold, calm stratosphere can produce a larger hole even when the chemistry is improving, and a warm, disturbed one can produce a smaller hole. For that reason, scientists look at long-term trends in ODS levels and in ozone, not at a single season. The WMO framed 2025 as consistent with the trend and not as proof by itself. That reading is our own summary of how the agencies describe variability.
What are ozone-depleting substances?
Ozone-depleting substances are human-made chemicals that release chlorine or bromine in the stratosphere. They were used in refrigeration, air conditioning, firefighting foam and hairspray. The Montreal Protocol, adopted on September 16, 1987, phased out those chemicals. It is widely regarded as the most successful environmental treaty and has near-universal ratification.
How much have ozone-depleting substances fallen?
Stephen Montzka, a senior scientist at NOAA’s Global Monitoring Laboratory, said that ODS levels in the Antarctic stratosphere have fallen by about a third relative to pre-ozone-hole levels since they peaked around the year 2000. NASA scientist Paul Newman said the hole would be more than one million square miles larger if chlorine levels were still as high as they were 25 years ago. Those two statements give a sense of scale: the treaty did not eliminate the hole, but it made it smaller than it would otherwise be.
When will the ozone layer recover?
The WMO and the United Nations Environment Programme (UNEP) co-sponsor a Scientific Assessment of Ozone Depletion every four years. The 2022 assessment projected recovery to 1980 values on the following schedule, assuming current policies stay in place.
- Rest of the world: around 2040
- Arctic: around 2045
- Antarctic: around 2066
The next assessment is due in 2026. Paolo Laj, chief of the WMO’s Atmospheric and Environment Research Section, said the ozone layer is on track to recovery and is expected to return to 1980s levels by mid-century. The WMO page uses both “1980s levels” and “1980 values” for the target, so the exact reference point is worth checking in the assessment itself.
Key dates at a glance
- September 16, 1987: the Montreal Protocol is adopted
- 1992: the year the Protocol took effect, and the starting point for NASA and NOAA’s ranking of hole sizes
- Around 2000: ozone-depleting substances in the Antarctic stratosphere peak
- 2006: the largest ozone hole ever observed
- 2022: the most recent completed WMO and UNEP assessment sets the recovery schedule
- December 1, 2025: the 2025 hole closes
- 2026: the next four-year assessment is due
Why did the Montreal Protocol work?
The agencies credit the treaty for cutting the chemicals that cause the hole. Its near-universal ratification means that almost every country is bound by the same phase-out. The WMO page does not analyze why the treaty succeeded, so we offer only the simple observation that the target was a defined list of chemicals with available alternatives. That observation is our own and not the agencies’ conclusion.
What does this mean for climate policy?
The ozone story is often cited as evidence that coordinated international action can work. It is a different problem from climate change, since ODS are not the main cause of warming, but some of the same refrigerant chemicals are also potent heat-trapping gases. Readers who want the wider energy picture can see our article on global CO2 emissions and our explainer on the greenhouse effect. The link between the two issues is a general one, and the WMO page we used does not discuss it.
What are the limits of the evidence?
Three limits apply. First, the hole-size figures are season averages and ranks, not a single peak value, because the WMO page does not give a peak-day maximum. Second, the recovery dates depend on policies staying in place, as the 2022 assessment states. Third, one agency’s ranking can differ slightly from another’s because of the measurement method. We report the figures as the agencies gave them.
Frequently asked questions
Is the ozone hole closing?
The 2025 hole closed on December 1, the earliest closure since 2019, and was smaller than in recent years. Long-term recovery is projected, not complete.
What caused the ozone hole?
Human-made ozone-depleting substances used in refrigeration, air conditioning, firefighting foam and hairspray.
When will the Antarctic ozone hole recover?
Around 2066, according to the 2022 assessment, if current policies stay in place.
What is the Montreal Protocol?
A treaty adopted on September 16, 1987 that phased out ozone-depleting chemicals and has near-universal ratification.