48th meeting of the Open-ended Working Group of the Parties

Title: Interlinkages between Climate and Ozone Treaties

Description: Methane (CH4) plays a well-established role in stratospheric ozone chemistry, recognised in the 1989 Vienna Convention for the Protection of the Ozone Layer. Its atmospheric oxidation in the stratosphere produces water vapour and hydrogen oxides (HOx), influencing both ozone destruction and formation. The net effect of current anthropogenic methane emissions is an increase in global stratospheric ozone levels, partially offsetting losses from other ozone-depleting substances (ODSs). However, this positive effect should not be considered a justification for continued methane emissions.

In a future where the Paris Agreement is successfully implemented, bringing large reductions in methane and CO2, nitrous oxide (N2O) will become the dominant anthropogenic ozone-depleting emission. This amplifies the need for urgent N2O mitigation alongside methane abatement. The Montreal Protocol framework has historically focused on halogenated ODSs, but scientific and political dialogue on the methane-ozone layer link could support synergies between climate and ozone regimes without undermining current commitments.

It is therefore useful to examine the interlinkages between the two treaties, as there is opportunity for policymakers to use the methane/ozone layer link to reinforce integrated action on methane and N2O, not to delay or weaken climate commitments.

Contact(s):

Denise San Valentin

denise.sanvalentin@un.org