The Montreal Protocol on Substances that Deplete the Ozone Layer, agreed in 1987, committed states to phasing out chlorofluorocarbons and other chemicals that destroy stratospheric ozone. Universally ratified and repeatedly strengthened, it has succeeded in cutting the production of the controlling substances and putting the ozone layer on a path to recovery. Because many of the banned chemicals were also potent greenhouse gases, it has delivered substantial climate benefit as well. It is widely regarded as the most effective global environmental treaty.
It is the benchmark of successful global environmental governance, proving that binding international agreement can reverse a planetary-scale problem and setting a precedent for later climate diplomacy.
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