The Montreal Protocol remains a landmark achievement in international environmental policy, having successfully reduced the production and use of many ozone-depleting substances (ODS). However, recent atmospheric observations have revealed trends that are inconsistent with the full implementation of the Protocol’s controls. This talk will explore how atmospheric records were used to detect unreported emissions of CFC-11, a banned chlorofluorocarbon, years after its global phase-out. I will also examine the ongoing case of HFC-23, a potent greenhouse gas and industrial by-product, whose emissions have persisted despite reports of near-total elimination in advance of the Kigali Amendment to the Protocol. These case studies, based on observations, modelling and Bayesian inference, illustrate the critical role of independent atmospheric monitoring in verifying compliance and identifying discrepancies. Additional emerging issues will be discussed, emphasizing the need for expanded, transparent, and globally coordinated observation networks to ensure the continued success of the Protocol and the protection of the stratospheric ozone layer and mitigation of climate change.

Prof. Matt Rigby is a Professor in the Atmospheric Chemistry Research Group at the University of Bristol. His research focusses on the interpretation of atmospheric measurements of greenhouse gases and ozone depleting substances. He is a member of the Advanced Global Atmospheric Gases Experiment (AGAGE) and leads the Investigating HALocarbon impacts on the Global Environment (InHALE) project. He has twice served as a lead author of the World Meteorological Organisation Scientific Assessment of Ozone Depletion.