The Montreal Protocol on Substances that Deplete the Ozone Layer is a global agreement to protect the Earth’s ozone layer by phasing out the chemicals that deplete it. This phase-out plan includes both the production and consumption of ozone-depleting substances. The landmark agreement was signed in 1987 and entered into force in 1989.
The parties to the Protocol meet once a year to make decisions aimed at ensuring the successful implementation of the agreement. These include adjusting or amending the Protocol, which has been done six times since its creation. The most recent amendment, the Kigali Amendment, called for the phase-down of hydrofluorocarbons (HFCs) in 2016. These HFCs were used as replacements for a batch of ozone-depleting substances eliminated by the original Montreal Protocol. Although they do not deplete the ozone layer, they are known to be powerful greenhouse gases and, thus, contributors to climate change.
The Montreal Protocol provided a set of practical, actionable tasks that were universally agreed on. The Protocol has successfully met its objectives thus far and continues to safeguard the ozone layer today. Thanks to the collaborative effort of nations around the world, the ozone layer is well on its way to recovery.
| Group | Substance | Ozone-Depleting Potential* |
| Group I | ||
| CFCl3 | (CFC‑11) | 1.0 |
| CF2Cl2 | (CFC‑12) | 1.0 |
| C2F3Cl3 | (CFC‑113) | 0.8 |
| C2F4Cl2 | (CFC‑114) | 1.0 |
| C2F5Cl | (CFC‑115) | 0.6 |
| Group II | ||
| CF2BrCl | (halon‑1211) | 3.0 |
| CF3Br | (halon‑1301) | 10.0 |
| C2F4Br2 | (halon‑2402) | 6.0 |
* These ozone depleting potentials are estimates based on existing knowledge and will be reviewed and revised periodically.