Narrowing uncertainties of halocarbon emissions and atmospheric lifetimes and their impacts on ozone recovery

Narrowing uncertainties of halocarbon emissions and atmospheric lifetimes and their impacts on ozone recovery 
Megan Lickley, assistant professor, Georgetown University Science, Technology, and International Affairs Program

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Chlorofluorocarbons and their replacement chemicals are potent greenhouse gases whose production is regulated under the Montreal Protocol.  These halocarbons are contained in equipment such as air conditioners, fire extinguishers, and foams and continue to be emitted after production has ceased. These ‘banks’ within equipment and applications are thus potential sources of future emissions, and must be carefully accounted for in order to evaluate ongoing compliance with the Montreal Protocol.  Quantifying bank emissions versus nascent emissions has been limited by large uncertainties in bank size as well as uncertainties in atmospheric lifetimes.  In this talk I will present a probabilistic Bayesian model of halocarbon banks and emissions, incorporating the widest range of constraints to date. I will show how jointly considering production and emissions of multiple gases can reduce uncertainty in lifetimes and ultimately better constrain banks, production and emissions estimates.  I apply this model to the suite of the major banked chemicals regulated under the Montreal Protocol.  Finally, I will discuss the extent to which changing assumptions of these values have led to a consistent delay in expected recovery over the past 16 years of scientific assessments. 

Bio: 

Dr. Megan Lickley is an Assistant Professor at Georgetown in the Science, Technology, and International Affair Program and The Earth Commons.  She received her PhD in atmospheric science from MIT in 2020.  Her research uses Bayesian methods to combine deterministic models with observations to target climate policy at multiple scales, from multilateral environmental agreements to local infrastructure planning.  Her recent work evaluates emissions, production and banks of chemicals regulated under the Montreal Protocol.  Her banks model has been adopted by the 2022 International Ozone Assessment, in which she is a co-author.