A decline in global CFC-11 emissions during 2018-2019.

Montzka, Stephen A; Dutton, Geoffrey S; Portmann, Robert W; Chipperfield, Martyn P; Davis, Sean; Feng, Wuhu; Manning, Alistair J; Ray, Eric; Rigby, Matthew; Hall, Bradley D; Siso, Carolina; Nance, J David; Krummel, Paul B; Mühle, Jens; Young, Dickon; O'Doherty, Simon; Salameh, Peter K; Harth, Christina M; Prinn, Ronald G; Weiss, Ray F; Elkins, James W; Walter-Terrinoni, Helen; Theodoridi, Christina

The atmospheric concentration of trichlorofluoromethane (CFC-11) has been in decline since the production of ozone-depleting substances was phased out under the Montreal Protocol1,2. Since 2013, the concentration decline of CFC-11 slowed unexpectedly owing to increasing emissions, probably from unreported production, which, if sustained, would delay the recovery of the stratospheric ozone layer1-12. Here we report an accelerated decline in the global mean CFC-11 concentration during 2019 and 2020, derived from atmospheric concentration measurements at remote sites around the world. We find that global CFC-11 emissions decreased by 18 ± 6 gigagrams per year (26 ± 9 per cent; one standard deviation) from 2018 to 2019, to a 2019 value (52 ± 10 gigagrams per year) that is similar to the 2008-2012 mean. The decline in global emissions suggests a substantial decrease in unreported CFC-11 production. If the sharp decline in unexpected global emissions and unreported production is sustained, any associated future ozone depletion is likely to be limited, despite an increase in the CFC-11 bank (the amount of CFC-11 produced, but not yet emitted) by 90 to 725 gigagrams by the beginning of 2020.