Another Surprising Turn in the Global Emission of CFC-11

Abstract:

It has been just over two years since we documented an unexpected increase in global CFC-11 emission. The emission increase is likely the result of renewed CFC-11 production and, therefore, suggests a violation of the Montreal Protocol on Substances that Deplete the Ozone Layer. If emissions remain elevated in the future, a substantial delay in ozone recovery would be expected. These findings prompted a substantial international response by scientists, industry, policymakers, and non-governmental organizations to elucidate the underlying causes for this apparent breach of the Protocol and ensure that the elevated emissions and enhanced ozone depletion be minimized. Despite these efforts, the underlying causes of the emission increase, and the region(s) responsible for much of this increase and all of the renewed production remain unclear. As atmospheric scientists, our role during this secondary phase of the issue can be to provide accurate and timely feedback on emission changes during the two years since mid-2018 when this issue was first raised. In this presentation, we will consider updated measurements of atmospheric CFC-11 at remote sites around the world from two independent networks, NOAA and AGAGE. These results provide an objective evidence-based means for deriving global emission magnitudes and their changes over time. We will also consider up-to-date 3-D global model analyses to estimate the influence of dynamical variability on the interpretation of our results, since this variability can substantially influence global emission rates and year-to-year changes when derived from surface measurements. In this talk we will discuss progress we have made in quantifying the impacts of non-emissive influences on trace gas abundances measured at Earth’s surface. By accounting for these influences, our initial results indicate a decline in global CFC-11 emissions since 2018, consistent with the successful elimination of a portion of the unexpected global emission increase. Implications of these results for future CFC-11 emissions and the timing of ozone-layer recovery will also be addressed.