The Antarctic ozone hole in 2025 was one of the smallest in recent decades, the World Meteorological Organization said in its annual Ozone Bulletin.

Last year’s hole ranked as the fourth or fifth smallest since severe depletion was first observed in 1992. It was the second straight year that both its depth and extent stayed well below the 1990-2010 average.

The ozone layer sits 15 to 30 kilometres above Earth and blocks nearly all harmful short-wave ultraviolet radiation from the Sun. It was damaged by chlorofluorocarbons (CFCs), gases once used in refrigerants, aerosol sprays and fire-fighting foam.

The recovery reflects the success of the Montreal Protocol of 1987, signed by 197 countries, which phased out ozone-depleting chemicals. WMO Secretary-General Celeste Saulo called it “an environmental success story”, saying the layer has been recovering since 2000 and could fully heal within decades.

Scientists caution that the hole’s size varies year to year with weather. Warming in the stratosphere last September slowed ozone destruction and helped keep the 2025 hole small.