The Montreal Protocol on Substances that Deplete the Ozone Layer

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.

Decision XXXV/4: Stratospheric aerosol injection and protection of the ozone layer

Taking note with appreciation of the 2022 quadrennial assessment report of the Scientific Assessment Panel[1] and its chapter 6 on stratospheric aerosol injection and its potential effect on the stratospheric ozone layer,

Noting that limited scientific information is available about the risks to the ozone layer of stratospheric aerosol injection,

Noting also the potential for negative effects that stratospheric aerosol injection may have on the ozone layer, including depleting stratospheric ozone, delaying recovery of the ozone layer, and influencing stratospheric chemistry,

  1. To invite the global scientific community to take into account risks and uncertainties for the ozone layer in any scientific studies or assessments undertaken in relation to stratospheric aerosol injection;
  2. To request the Scientific Assessment Panel to engage with the global scientific community regarding, and to continue to bring to the attention of the parties, any important developments with respect to stratospheric aerosol injection, including the inclusion of updated or new scenarios or modelling to assist with understanding of the potential impacts of stratospheric aerosol injection on the ozone layer.

[1] World Meteorological Organization, Scientific Assessment of Ozone Depletion: 2022, GAW Report No. 278 (Geneva, 2022).