A Smaller Ozone Hole Shows What Global Action Can Achieve

The size of the Antarctic ozone hole changes from year to year because atmospheric conditions influence how much ozone disappears after the southern winter.

The Antarctic ozone hole was one of the smallest in recent decades in 2025, offering an encouraging sign that the international effort to repair Earth's protective ozone layer is delivering results. According to the World Meteorological Organization (WMO), last year's hole ranked as the fourth to fifth smallest since severe depletion patterns were observed in 1992, making it the second consecutive year that both its depth and extent stayed significantly below the 1990–2010 average.

For people who remember warnings about chemicals eating away at the planet's natural sunscreen, the findings show the lasting value of decisions made nearly four decades ago. The Montreal Protocol, adopted in 1987, helped countries phase out ozone-depleting substances used in refrigeration and other everyday applications, setting in motion a recovery that scientists expect to continue over the coming decades.

Recovery Takes More Than One Good Year

The size of the Antarctic ozone hole changes from year to year because atmospheric conditions influence how much ozone disappears after the southern winter. A smaller hole is welcome news, though scientists need decades of measurements to separate the effects of changing weather patterns from the recovery driven by falling levels of ozone-depleting chemicals. WMO Secretary-General Celeste Saulo described the progress as an environmental success story, with recovery underway since 2000 and full recovery expected within several decades.

Conditions across the Northern Hemisphere show why a single headline cannot capture the whole picture. During 2025, total column ozone was below average across a broad region stretching from Greenland and Europe to Central Asia, northern Japan and Russia's Kamchatka Peninsula. Such regional differences sit within the broader recovery trend and underline the importance of observations that track changes across the globe.

A Healing Ozone Layer Does Not Remove UV Risks

Around 90% of atmospheric ozone sits in the stratosphere, where it absorbs nearly all of the Sun's dangerous short-wave ultraviolet radiation. Compressed down to Earth's surface, that ozone would form a layer only about three millimetres thick, a remarkably thin shield for the protection it provides. Its recovery matters for human health, though the amount of UV radiation reaching people also depends on cloud cover and the duration of sunshine.

Measurements cited in the WMO bulletin show that UV radiation has increased by as much as 20% in some parts of Europe since the mid-1990s, driven mainly by fewer clouds and longer sunshine duration. Greater exposure raises the risk of skin cancer and other UV-related diseases, giving public health authorities a reason to keep UV protection firmly on the agenda even as the ozone layer heals.

Keeping Watch on a Global Success

Released for World Ozone Day on 16 September, the bulletin also recognises the Montreal Protocol's wider climate role through the 2016 Kigali Amendment. The amendment provides for a phased reduction in hydrofluorocarbons, or HFCs, used in cooling technologies and other equipment. These gases do not damage ozone, but some trap thousands of times more heat than carbon dioxide, making their reduction an important part of efforts to limit warming.

Continued progress depends on knowing what is entering the atmosphere, particularly after unexpected emissions of controlled substances exposed gaps requiring regulatory attention. The number of active stations using traditional ozone-monitoring instruments has fallen from around 130 in the early 2000s to about 110, with closures often affecting places where measurements are already scarce. Newer instruments have expanded rapidly, but their focus on air quality leaves an ongoing need for dedicated observations of the ozone layer that protects life below.