The ozone hole over Antarctica in 2025 was among the smallest in recent decades, according to a new bulletin from the World Meteorological Organization (WMO). The agency regards the result as a positive sign of the ozone layer’s recovery, but notes that the size of the hole varies from year to year.
According to the WMO Ozone Bulletin, the extent and depth of the hole recorded last year were significantly below the 1990-2010 average. It was also the second consecutive year in which both indicators remained below that reference.
The WMO indicates that the 2025 hole ranked between the fourth and fifth smallest since 1992, when patterns of particularly pronounced ozone layer destruction began to be observed.
Despite the positive evolution, researchers warn that it is not possible to interpret the values of a single year in isolation. Weather conditions and the transport of air masses in the atmosphere influence the seasonal destruction of ozone and help explain the annual fluctuations.
A Montreal Protocol success
The trend observed in recent years is, however, part of a long-term recovery that the WMO attributes to the reduction of substances that destroy the ozone layer.
The Montreal Protocol, adopted in 1987, established the progressive elimination of substances such as chlorofluorocarbons (CFCs), which were used, among other applications, in refrigeration systems and foams.
“It is an environmental success story. Since 2000, the ozone layer has been recovering and we can expect a full recovery within several decades,” said Celeste Saulo, the WMO secretary-general.
Atmospheric measurements made over the past four decades show a significant reduction in the concentrations of several substances controlled by the Montreal Protocol. Still, unexpected emissions of some compounds were detected, which led the WMO to reinforce the importance of continuous atmospheric monitoring.
Less ozone is not the only concern
The recovery of the ozone layer does not mean that exposure to ultraviolet (UV) radiation no longer poses a risk.
About 90% of atmospheric ozone is located in the stratosphere, where it acts as a barrier to UV radiation harmful from the Sun. The WMO warns, however, of an increase in the number of days with high UV indices observed in recent decades.
In some regions of Europe, UV radiation has increased by as much as 20% since the mid-1990s. According to the agency, this trend is mainly due to a reduction in cloud cover and an increase in the annual duration of sunshine, and not directly to the recovery or depletion of the ozone layer.
Greater exposure to UV radiation increases the risk of skin cancer and other diseases associated with ultraviolet radiation, so the WMO considers that appropriate protective measures are necessary.
The next challenge also involves HFCs
The Montreal Protocol was subsequently strengthened by the Kigali Amendment, adopted in 2016, which established a progressive reduction of hydrofluorocarbons (HFCs).
HFCs do not destroy the ozone layer, but they are potent greenhouse gases and are used in refrigeration and air conditioning equipment, among other applications. Some can trap thousands of times more heat than carbon dioxide, though they remain in the atmosphere for a shorter period.
The WMO also stresses the importance of maintaining atmospheric monitoring networks. The number of active stations equipped with traditional ozone measurement instruments has fallen from around 130 at the start of the 2000s to about 110 today, including in regions where observations are particularly scarce.
Monitoring data are considered essential to track the recovery of the ozone layer, detect unexpected emissions of regulated substances, and support future environmental policy decisions.
