World Ozone Day

The International Ozone Commission, on the 38th anniversary of the Montreal Protocol, underscores the success of the protocol, and stresses the value of continued observations, modeling, and research.

The 38th International Day for the Preservation of the Ozone Layer, September 16, 2025, marks
the anniversary of the signing of the 1987 Montreal Protocol on Substances that Deplete the
Ozone Layer. This protocol, a treaty signed by every country in the world and hailed as among
the most successful international agreements to date, controls the production and use of ozone
depleting substances (ODSs) such as chlorofluorocarbons (CFCs) and the other substances
used as initial CFC replacements. As a result of the actions taken worldwide in response to the
protocol and its amendments and adjustments, atmospheric abundances of ODSs are declining,
and the stratospheric ozone layer, which shields life on Earth from harmful solar ultraviolet
radiation, is showing clear signs of recovery.
The theme of the 2025 International Day for the Preservation of the Ozone layer, “From science
to global action”, acknowledges the success of the protocol, an accomplishment whose success
was critically dependent on sustained long-term cooperation between scientists, industry, and
governments.
This year also marks the 40th anniversary of the adoption of the Vienna Convention for the
Protection of the Ozone Layer, in which countries agreed to undertake cooperative scientific
studies of the processes affecting the ozone layer and to regularly report on its health.
Furthermore, it is also 40 years since the publication in 1985 of the landmark paper by Farman,
Gardiner, and Shanklin that reported a steep decline in the amount of ozone above Antarctica
during springtime, starting in the mid-1970s. Crucially, there were no then-known processes that
could account for the existence of this “ozone hole”. These observations spurred many research
efforts in the subsequent years, including measurement campaigns, laboratory studies, and
modeling activities, all aimed at identifying the processes involved.
The 1985 discovery of the ozone hole underscores the ability of the atmosphere (and the Earth
system more broadly) to “surprise” the scientific community. It serves as a reminder of the
importance of long-term observations of key Earth system parameters, using a robust, accurate,
and well-understood measurement system based on complementary observations sampling the
atmosphere directly from balloons and aircraft and remotely both from the ground and space.
Continuation of such measurements, and of associated laboratory studies and modeling efforts
needed to robustly explain observed ozone changes, is essential for avoiding further surprises
and for ensuring that trajectories which endanger the well-being of human society and life on
Earth are avoided.
This reminder is particularly timely given the potential loss of funding for long-established
observing systems (spaceborne, ground-based, and balloon-borne) and science research that
are essential for tracking ozone layer recovery. The International Ozone Commission (io3c.org)
urges governments worldwide to continue the essential work of monitoring, diagnosing, and
verifying ozone layer recovery.
For more information contact: Dr. Corinne Vigouroux, Secretary of the International Ozone
Commission, Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Ringlaan 3, 1180 Uccle,
Belgium, Corinne.Vigouroux@aeronomie.be.

● IO3C: http://www.io3c.org
● United Nations Environment Program’s Ozone Secretariat World Ozone Day 2025:
https://ozone.unep.org/ozone-day/from-science-to-global-action
● WMO Northern Hemisphere Ozone Mapping Center: http://lap.physics.auth.gr/ozonemaps
● World Ozone and Ultraviolet Data Center: http://www.woudc.org
● O3 Global: http://www.temis.nl/protocols/O3global.html
● Ozone Hole Watch: http://ozonewatch.gsfc.nasa.gov/
● World Meteorological Organization (WMO). Scientific Assessment of Ozone Depletion:
2022, GAW Report No. 278, 509 pp.; WMO: Geneva, 2022.
https://ozone.unep.org/science/assessment/sap