Quantifying contributions of chlorofluorocarbon banks to emissions and impacts on the ozone layer and climate

Abstract

Chlorofluorocarbon (CFC) banks from uses such as air conditioners or foams can be emitted after global production stops. Recent reports of unexpected emissions of CFC-11 raise the need to better quantify releases from these banks, and associated impacts on ozone depletion and climate change. Here we develop a Bayesian probabilistic model for CFC-11, 12, and 113 banks and their emissions, incorporating the broadest range of constraints to date. We find that bank sizes of CFC-11 and CFC-12 are larger than recent international scientific assessments suggested, and can account for much of current estimated CFC-11 and 12 emissions (with the exception of increased CFC-11 emissions after 2012). Left unrecovered, these CFC banks could delay Antarctic ozone hole recovery by about six years and contribute 9 billion metric tonnes of equivalent CO 2 emission. Derived CFC-113 emissions are subject to uncertainty, but are much larger than expected, raising questions about its sources.

Joint inference of CFC lifetimes and banks suggests previously unidentified emissions

“…both bank and illicit emissions). Earlier work has focused on 46 quantifying the size of CFC banks and potential contributions to future emissions 6 ; here we focus on jointly estimating lifetimes of CFC-11, 12 and 113 as well as the magnitude and sources of global emissions of these gases using all available information in a 49 probabilistic framework. 50…”

“…Adding these new constraints to the BPE model bank emissions over time. In this way, we can better quantify and partition recent emissions into bank emissions versus unexpected sources using all available information.To derive lifetimes, emissions and their respective sources, we build on the Bayesian 152Parameter Estimation approach to modeling banks and emissions developed by Lickley 153 and colleagues6 . The basic framework develops a bottom-up simulation model that 154 simultaneously models banks, emissions (partitioned into bank emissions versus direct 155 emissions), and mole fractions over time.…”

“…using eq 1 of Methods). This provides a useful contrast to 183 previous emissions comparisons fromLickley et al (2020) 6 , which adopted both a time-184 varying lifetime and constant scenario equal to the SPARC multi-model mean. 185Compared to Lickley et al (2020), the posterior emissions in Figure 2 show a closer 186 match between parameter-based and observationally derived emissions as well as lower 187 uncertainties, which can be explained in part by lifetimes being inferred instead of 188 as a distribution instead of fixed values, and our simulated emissions and 190 mole fractions are assumed to have lower uncertainty than in the Lickley et al (2020), 191 where lifetimes were fixed.…”

Australian chlorofluorocarbon (CFC) emissions: 1960–2017

“…Global summed emissions of CFC-11, CFC-12 and CFC-113 from atmospheric observations peaked at 1090 Gg in 1987-88 and at 1050 AE 90 (95 % confidence interval, CI) Gg in 1987-88 from a model estimating emissions from CFC production, consumption and 'banks' -so-called 'bottom-up' estimates ( Fig. 1; Rigby et al 2014;Engel and Rigby 2018;Prinn et al 2018;Lickley et al 2020). These declining CFC emissions translate into a significant decline (,90 %) in carbon dioxide equivalent (CO 2 -e) emissions of 8000 Tg (1 Tg ¼ 10 3 Gg) over the same period (Fig.…”

“…Avoiding these increased CFC-11 emissions could have a larger positive impact on stratospheric ozone than any other policy option considered in the latest assessment of stratospheric ozone depletion, including destruction of the CFCs still existing in CFC 'banks' found in foams, refrigeration and air conditioning equipment (Carpenter and Daniel 2018). However, recent re-evaluations of the magnitude of global CFC banks, and their related CFC emissions, indicate they may be underestimated (Lickley et al 2020) and destruction of the CFC banks may be comparable, in relation to ozone recovery, to avoiding the increased CFC emissions from east Asia.…”