The 2018 UNEP/WMO Scientific Assessment of Ozone Depletion

The “Scientific Assessment of Ozone Depletion: 2018” is the latest in a long series that is mandated by the Parties to the Montreal Protocol (MP) every four years. It is authored by a large international group of scientists and managed by the Scientific Assessment Panel of the Montreal Protocol. The Executive Summary of the 2018 assessment was released to the Parties and the public in September 2018 and was followed by the underlying assessment chapters in late-December 2018. Since the 1987 adoption of the MP, the atmospheric abundances of controlled ozone-depleting substances (ODSs) have decreased substantially and the recovery of stratospheric ozone in underway. The assessment highlights that Antarctic ozone is still occurring with signs of recovery and that upper stratospheric ozone has increased outside polar regions. In global ozone, no significant upward trend has yet been observed. Future scenarios of global ozone identify recovery milestones around mid-century for ozone returning to 1980 abundances in different regions.

Important events since the 2014 assessment include the adoption of the Kigali Amendment to phasedown global production of hydrofluorocarbons (HFCs), which are used to replace ODSs in many applications. The avoided emissions resulting from the global phasedown are projected to reduce future global average warming in 2100 due to HFCs from a baseline of 0.3-0.5˚C to less than 0.1˚C. In addition, an unexpected increase in global total emissions of CFC-11 has been derived from time series of surface observations at remote sites. The increase has slowed the atmospheric removal of CFC-11, one of the most abundant ODSs in the atmosphere. This presentation will discuss these highlights as well as the assessment process and its role in the Montreal Protocol.