A Method for Calculating Offsets to Ozone Depletion and Climate Impacts of Ozone-Depleting Substances.

By phasing out production and consumption of most ozone depleting substances (ODSs), the Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol) has avoided consequences of increased ultraviolet (UV) radiation, and it will restore stratospheric ozone to pre-1980 conditions by mid-century, assuming compliance with the phaseout. However, several studies have documented an unexpected increase in emissions and unreported production of trichlorofluoromethane (CFC-11) and other ODSs that occurred after 2012 despite production phaseouts under the Montreal Protocol. Furthermore, because most ODSs are powerful greenhouse gases there are significant climate protection benefits in collecting and destroying the substantial quantities of historically allowed products under the Montreal Protocol that are contained in existing equipment and products and referred to as ODS "banks". Here we present a framework for considering offsets to ozone depletion, climate forcing, and other environmental impacts arising from this or other occurrences of unexpected emissions and unreported production of Montreal Protocol controlled substances. We also show how this methodology could be applied to the destruction of banks of controlled ODSs and GHGs, or to halon or other production allowed under a Montreal Protocol Essential Use Exemption or emergency exemption. Further, we explore a range of potential actions that could offset the ozone depletion, climate, and other environmental impacts arising from instances of unexpected emissions or unreported production should Montreal Protocol Parties agree require remedial action. [ABSTRACT FROM AUTHOR]