The Montreal Protocol: how today’s successes offer a pathway to the future

The Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol) is widely considered to be the most successful multilateral environmental agreement (MEA) because: 1) it is working to protect the ozone layer, 2) it is the only treaty that enjoys universal membership, and 3) both developing and developed countries are committed to phasing out controlled ozone-depleting substances (ODSs) and are almost continuously in full compliance with the phase-out schedule. In addition, the abundance of ozone-depleting chlorine and bromine from manufactured chemicals is declining and is expected to continue to decline in the stratosphere to pre-Antarctic ozone hole levels by the middle of this century. The Montreal Protocol is a double success because the phase out of ODSs also protects the climate. Most ODSs are powerful greenhouse gases (GHGs), while many alternatives to ODSs are not or have lower global warming potential than the ODSs they replace. Furthermore, although the Kyoto Protocol already controls emissions of certain alternatives to ODSs that are powerful GHGs, amendments to the Montreal Protocol are proposed to control both their production and consumption. This paper explains how the Montreal Protocol has achieved its success and raises questions of practical and academic interest as to how the Montreal Protocol can guard against backsliding, loopholes, illegal trade, and other actions that are threatening, making the world safe for future generations. It also explores how the Kyoto and Montreal Protocols can be made stronger and more cost-effective by taking advantage of the synergy of separate and joint actions.