The WMO Ozone Bulletin reported that the low level of ozone depletion observed in 2024 was partly due to naturally occurring atmospheric factors which drive year-to-year fluctuations. However, the long-term positive trend reflects the success of concerted international action.

The WMO Ozone Bulletin was issued for World Ozone Day on 16 September and the 40th anniversary of the Vienna Convention, which recognized stratospheric ozone depletion as a global problem and provided the framework for mobilizing international cooperation in ozone research, systematic observations and scientific assessments.

“Forty years ago, nations came together to take the first step in protecting the ozone layer — guided by science, united in action,” said United Nations Secretary-General António Guterres.

“The Vienna Convention and its Montreal Protocol became a landmark of multilateral success.  Today, the ozone layer is healing. This achievement reminds us that when nations heed the warnings of science, progress is possible,” he said.

To date, the Montreal Protocol has led to the phase-out of over 99% of the production and consumption of controlled ozone-depleting substances, which were used in refrigeration, air conditioning, firefighting foam and even hairspray. As a result, the ozone layer is now on track to recover to 1980s levels by the middle of this century, significantly reducing risks of skin cancer, cataracts, and ecosystem damage due to excessive UV exposure.

“The theme for World Ozone Day is From Science to Global Action. It mirrors WMO’s 75th anniversary slogan Science for Action. This is no coincidence,” said WMO Secretary-General Celeste Saulo.

“WMO’s scientific research into the ozone layer dates back decades. It is underpinned by trust, international collaboration and commitment to free data exchange – all cornerstones of the world’s most successful environmental agreement,” she said.

Sustainable development goals

The WMO Ozone Bulletin is one of a suite of products issued by WMO’s Global Atmosphere Watch Programme to inform policy-making.

Scientists first sounded the alarm back in 1975, when WMO issued a statement “Modification of the ozone layer due to human activities and some possible geophysical consequences."

“Despite the great success of the Montreal Protocol in the intervening decades, this work is not yet finished, and there remains an essential need for the world to continue careful systematic monitoring of both stratospheric ozone and of ozone-depleting substances and their replacements,” said Matt Tully, Chair of WMO’s Scientific Advisory Group on Ozone and Solar UV Radiation.

Protecting the ozone layer and thereby human, environmental and agricultural health has enabled significant progress towards achieving many of the United Nations Sustainable Development Goals, including SDG 3 (Good Health and Well-Being), SDG 13 (Climate Action), SDG 2 (Zero Hunger) and SDG 15 (Life on Land), he said.

Deviation of recent annual mean total ozone columns from the geographic long-term average distribution. A dobson unit (DU) represents the integrated amount of ozone in the atmospheric column; 300 DU is a typical level for mid-latitudes, but this value can be higher or lower in the polar and tropical regions, respectively.

Third-party map. This map was provided by Wolfgang Steinbrecht and Antje Inness on 11 July 2025 and may not fully align with United Nations and WMO map guidance. Results are from the Copernicus Atmospheric Monitoring Service Reanalysis (Inness et al., 2019)

Compared to previous years, total stratospheric ozone cover was higher over much of the globe, according to the WMO Bulletin.

The depth of 2024 Antarctic ozone hole – which appears over the Antarctic every spring - was below the 1990–2020 average, with a maximum ozone mass deficit (OMD) of 46.1 million tonnes on 29 September. It was smaller than the relatively large holes between 2020 and 2023.

Its onset was relatively slow, and delayed ozone depletion was observed through the month of September, followed by a relatively rapid recovery after the maximum deficit was reached.

“This persistent later onset has been identified as a robust indication of initial recovery of the Antarctic ozone hole,” said the Bulletin.

Importance of monitoring

In support of the Montreal Protocol, the WMO-led community developed and implemented guiding principles for ozone and ultraviolet (UV) monitoring networks. These principles aim to ensure broad observational coverage, define standards for operations, data processing and calibrations, and foster a network where scientists meet, exchange knowledge, receive training and explore opportunities for collaboration.

This approach has proven invaluable for enabling effective and policy-relevant observations, and it is one of the keys to the success of the Montreal Protocol, according to one of the articles in the Bulletin which explores measuring instruments and intercomparison campaigns.