NASA and NOAA scientists ranked the 2025 Antarctic ozone hole as the fifth smallest since 1992, a finding that reflects decades of global chemical regulation but does not mean the threat has passed. The hole still formed this year over Antarctica during Southern Hemisphere spring, and natural disruptions like volcanic eruptions continue to complicate the recovery timeline. The short answer to whether the ozone hole is truly gone is that it is not, but it is shrinking in ways that science can now trace directly to policy action.
The 2025 Ozone Hole by the Numbers
Measured by satellite instruments, the ozone hole is typically defined as the area where ozone concentration drops below 220 Dobson Units south of 40 degrees latitude, according to long-running NASA monitoring updated through October 2025. By that standard, the hole still appears every year during the Antarctic winter and spring, then closes as temperatures warm and sunlight returns. The 2025 season produced one of the smallest holes in decades, and the Copernicus Atmosphere Monitoring Service reported that it closed on December 1, the earliest closure since 2019 and much earlier than the persistently large and long-lived holes seen in the early 2000s.
Using 46 years of satellite and balloon observations, this year’s hole ranked 14th smallest over the full record, but the more policy-relevant comparison is the post-1992 period when ozone-depleting substances were near their peak. In that window, a joint analysis by NASA and NOAA placed 2025 as the fifth smallest Antarctic ozone hole, underscoring a sustained improvement since the worst years. The record low for October ozone concentration occurred in 2006, when chemical depletion and favorable meteorological conditions coincided; by contrast, 2025 saw higher minimum values and a smaller maximum area, signaling that the underlying chemistry of the stratosphere is gradually becoming less hostile to ozone.
Fingerprinting Recovery to the Montreal Protocol
A recurring criticism of upbeat ozone news is that a small hole in any single year might simply reflect unusual weather rather than genuine chemical healing. A 2025 study in Nature by Wang and colleagues directly tested that concern using a detection-and-attribution framework that separates the signal of declining chlorine and bromine from the noise of natural variability. By comparing modeled scenarios with and without policy controls to actual observations, the authors were able to isolate the recovery signal associated with reduced emissions of chlorofluorocarbons and related compounds. Their conclusion was that the observed Antarctic ozone increase since the late 1990s is dominated by the chemical impact of the Montreal Protocol and its subsequent amendments, not by a lucky run of benign polar weather.
The chemical backdrop for that conclusion is quantified by NOAA’s Ozone Depleting Gas Index, which tracks the combined effect of chlorine- and bromine-bearing gases in the lower atmosphere and converts them into an estimate of their eventual impact in the stratosphere. The index incorporates the time it takes for air to ascend into the upper atmosphere and the greater efficiency of bromine in destroying ozone, producing a single number that declines only as long-lived compounds slowly break down. Even though production of most major ozone-depleting substances ended years ago, the index shows that a substantial reservoir remains aloft, explaining why the ozone hole still appears each spring even as its average size and depth trend downward.
Why the Danger Has Not Fully Passed
Natural events can temporarily derail this slow improvement. The January 2022 eruption of the Hunga Tonga (Hunga Ha‘apai) volcano injected an unprecedented pulse of water vapor into the stratosphere, altering the chemistry of ozone destruction in ways that were only fully quantified later. A study led by Evan and collaborators, summarized by NOAA researchers, documented accelerated ozone loss following that injection, particularly in the Southern Hemisphere. The added moisture promoted the formation of polar stratospheric clouds, whose icy surfaces host reactions that convert inert chlorine compounds into active, ozone-destroying forms; the result was a measurable, eruption-driven dip in ozone that came on top of the ongoing human-caused depletion.
Climate change adds a second, more persistent complication. While greenhouse gases warm the surface and lower atmosphere, they tend to cool the stratosphere, strengthening the polar vortex and extending the cold, dark conditions that favor ozone loss each winter and spring. Analyses of the year-to-year ozone record reveal that some of the largest holes on record occurred in years with especially strong, stable vortices, even after chlorine levels had begun to decline. At the same time, the ozone hole itself has altered Southern Hemisphere wind patterns and circulation, feeding back on climate and complicating projections of how quickly the system will return to its pre-industrial state. Together, these factors mean that even in a world with falling halogen levels, future years could still produce anomalously large or long-lived holes.
What Full Recovery Actually Looks Like
The most comprehensive projections for the ozone layer’s future come from the quadrennial scientific assessments coordinated under the auspices of the World Meteorological Organization and the United Nations Environment Programme. The latest of these, published in 2022 as GAW Report No. 278, synthesizes observational records, emission inventories, and chemistry–climate model simulations into a detailed set of timelines for different regions and altitudes. According to this global assessment, Antarctic springtime ozone is expected to return to its 1980 baseline levels around the middle of this century if compliance with the Montreal Protocol continues and no major new sources of ozone-depleting substances emerge. Mid-latitude ozone, which never declined as dramatically as over the pole, is projected to recover somewhat earlier, while the Arctic—more sensitive to year-to-year weather swings—shows a broader range of possible dates.
Recovery, however, does not mean that the ozone layer will look exactly as it did in 1980. The same chemistry–climate models used in the assessment indicate that rising greenhouse gases will continue to reshape stratospheric temperatures and circulation, subtly changing where and when ozone is produced and destroyed. Agencies such as NASA and NOAA emphasize that “pre-depletion levels” refer to broad benchmarks in total column ozone rather than a perfect re-creation of past patterns. In practical terms, full recovery will be recognized when the frequency of extremely low ozone events drops back to historical norms, the average thickness of the layer stabilizes or increases across latitudes, and the Antarctic hole ceases to dominate springtime conditions in the Southern Hemisphere as it has for the past four decades.
Lessons for Global Environmental Policy
The 2025 ozone hole, small by recent standards but still a recurring feature of the Antarctic sky, illustrates both the power and the limits of international environmental agreements. On the one hand, the combination of observational evidence from satellites, balloon sondes, and ground-based instruments and the statistical “fingerprints” identified in peer-reviewed studies shows that the Montreal Protocol has bent the curve of atmospheric chemistry in a measurable way. The decline in the Ozone Depleting Gas Index, the gradual rise in Antarctic springtime ozone, and the ranking of 2025 as the fifth smallest hole since 1992 collectively demonstrate that coordinated action on long-lived pollutants can reverse even severe global-scale damage, albeit on multi-decade timescales.
On the other hand, the lingering annual appearance of the hole, the sensitivity of ozone to volcanic eruptions and stratospheric water vapor, and the intertwined effects of climate change all underscore that success is neither instantaneous nor guaranteed. Continued monitoring by national and international agencies, enforcement of existing controls, and vigilance against new or unexpected emissions will be essential to keep the recovery on track. As policymakers look to tackle other atmospheric challenges, from greenhouse gases to short-lived climate pollutants, the story unfolding over Antarctica in 2025 offers a cautiously hopeful template: decisive, science-based regulation can work, but the atmosphere remembers our choices for generations, and the path back from the brink is long, uneven, and impossible to rush.
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*This article was researched with the help of AI, with human editors creating the final content.
