Montreal Protocol

The Montreal Protocol on Substances that Deplete the Ozone Layer is a protocol to the 1985 Vienna Convention for the Protection of the Ozone Layer. It was adopted on 16 September 1987 in Montreal and entered into force on 1 January 1989. The treaty commits parties to phasing down and eventually eliminating the production and consumption of ozone-depleting substances (ODS), including chlorofluorocarbons (CFCs), halons, carbon tetrachloride, methyl chloroform, hydrochlorofluorocarbons (HCFCs), and methyl bromide.

Key design features explain why the Protocol is widely regarded as the most successful multilateral environmental agreement:

• Common but differentiated responsibilities. Developing countries operating under Article 5 receive longer phase-out timetables and financial assistance.
• Multilateral Fund. Established in 1991, it finances ODS phase-out projects in developing countries and is administered with UNEP, UNDP, UNIDO, and the World Bank as implementing agencies.
• Trade measures. Parties restrict trade in controlled substances with non-parties, creating strong incentives to join.
• Adjustment and amendment mechanism. The Protocol can be tightened without renegotiation; major amendments were adopted in London (1990), Copenhagen (1992), Montreal (1997), Beijing (1999), and Kigali (2016).

The Kigali Amendment, adopted on 15 October 2016 and entering into force on 1 January 2019, extended the regime to hydrofluorocarbons (HFCs)—potent greenhouse gases used as CFC and HCFC replacements—linking ozone protection to climate mitigation. UNEP estimates the Kigali phasedown could avoid up to roughly 0.4°C of warming by 2100.

The Montreal Protocol achieved universal ratification, with all UN member states plus the EU, Holy See, Niue, Cook Islands, and the State of Palestine as parties. Scientific assessments by the WMO and UNEP indicate the Antarctic ozone hole is on a recovery trajectory, with full mid-latitude recovery projected around mid-century.