Montreal Protocol

The Montreal Protocol on Substances that Deplete the Ozone Layer was signed on September 16, 1987, and entered into force on January 1, 1989. It was negotiated under the framework of the Vienna Convention for the Protection of the Ozone Layer, adopted in 1985. The protocol has been amended several times, most notably in London (1990), Copenhagen (1992), and Kigali (2016).

The Montreal Protocol is widely considered the most successful international environmental treaty ever enacted. The ozone layer is projected to recover to 1980 levels by around the middle of the 21st century over most of the world, with the Antarctic ozone hole expected to heal by approximately the 2060s. Global production of CFCs has been reduced by over 98% since the protocol entered into force.

The Montreal Protocol is the only UN treaty to achieve universal ratification—all 197 UN member states are parties. This makes it the most universally ratified treaty in the history of international law. Every recognized country on Earth has committed to phasing out ozone-depleting substances.

The protocol mandates the phase-out of chlorofluorocarbons (CFCs), halons, carbon tetrachloride, methyl chloroform, and hydrochlorofluorocarbons (HCFCs). The Kigali Amendment, adopted in 2016, extended controls to hydrofluorocarbons (HFCs), which do not deplete ozone but are potent greenhouse gases. The HFC phase-down alone is projected to prevent up to 0.5°C of global warming by the end of the century.