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

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

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review


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 layer1,2,3,4,5,6,7,8,9,10,11,12. 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.
Original languageEnglish
Pages (from-to)428-432
Number of pages5
Issue number7846
Early online date10 Feb 2021
Publication statusPublished - 18 Feb 2021


  • Atmospheric chemistry
  • Atmospheric dynamics
  • Environmental impact

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