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Global increase of ozone-depleting chlorofluorocarbons from 2010 to 2020

An Author Correction to this article was published on 18 May 2023

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The production of chlorofluorocarbons (CFCs) that would ultimately be released to the atmosphere was banned globally in 2010 under the Montreal Protocol. Here we use measurements combined with an atmospheric transport model to show how atmospheric abundances and emissions of five CFCs increased between 2010 and 2020, contrary to the goals of the phase-out. The Montreal Protocol allows CFC production for use as a feedstock to produce other chemicals. Emissions of CFC-113a, CFC-114a and CFC-115 probably arise during the production of hydrofluorocarbons, which have replaced CFCs for many applications. The drivers behind increasing emissions of CFC-13 and CFC-112a are more uncertain. The combined emissions of CFC-13, CFC-112a, CFC-113a, CFC-114a and CFC-115 increased from 1.6 ± 0.2 to 4.2 ± 0.4 ODP-Gg yr-1 (CFC-11-equivalent ozone-depleting potential) between 2010 and 2020. The anticipated impact of these emissions on stratospheric ozone recovery is small. However, ongoing emissions of the five CFCs of focus may negate some of the benefits gained under the Montreal Protocol if they continue to rise. In addition, the climate impact of the emissions of these CFCs needs to be considered, as their 2020 emissions are equivalent to 47 ± 5 TgCO2.

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Fig. 1: Atmospheric abundances and growth rates.
Fig. 2: Global emissions weighted by impact on ozone depletion and climate.

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Data Availability

AGAGE data are available at (last accessed 16 November 2022) and ref. 51. NOAA atmospheric observations are available at and (last accessed 16 November 2022). All inputs to the 12-box model and the resultant estimated emissions, mole fractions and their growth rates are available at (last accessed 16 November 2022) or ref. 52, which also contains measurements analysed at UEA/FZJ.

Code Availability

The 12-box model and the inverse method used to quantify emissions are available via GitHub ( (last accessed 16 November 2022) and (last accessed 16 November 2022)) and Zenodo ( ref. 53 and ref. 54). Additional code to prepare inputs is available at (last accessed 16 November 2022) and ref. 52.

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We are indebted to UEA, FZJ, NOAA and AGAGE staff and scientists for their dedication to producing high-quality atmospheric trace gas measurements. The AGAGE Medusa GC-MS system development, calibrations and measurements at the Scripps Institution of Oceanography, La Jolla and Trinidad Head, CA, USA; Mace Head, Ireland; Ragged Point, Barbados; Cape Matatula, American Samoa; and Kennaook/Cape Grim, Australia were supported by the NASA Upper Atmospheric Research Program in the United States with grants NNX07AE89G, NNX16AC98G and 80NSSC21K1369 to MIT and NNX07AF09G, NNX07AE87G, NNX16AC96G, NNX16AC97G, 80NSSC21K1210 and 80NSSC21K1201 to SIO. The Department for Business, Energy & Industrial Strategy (BEIS) in the United Kingdom supported the University of Bristol for operations at Mace Head, Ireland (contract 1028/06/2015) and through the NASA award to MIT with sub-award to University of Bristol for Mace Head and Barbados (80NSSC21K1369). The National Oceanic and Atmospheric Administration (NOAA) in the United States supported the University of Bristol for operations at Ragged Point, Barbados (contract 1305M319CNRMJ0028) and operations at Cape Matatula, American Samoa. In Australia, the Kennaook/Cape Grim operations were supported by the Commonwealth Scientific and Industrial Research Organization (CSIRO), the Bureau of Meteorology (Australia), the Department of Climate Change, Energy, the Environment and Water (Australia), Refrigerant Reclaim Australia and through the NASA award to MIT with sub-award to CSIRO for Cape Grim (80NSSC21K1369). Measurements at Jungfraujoch are supported by the Swiss National Programs HALCLIM and CLIMGAS-CH (Swiss Federal Office for the Environment, FOEN) and by the International Foundation High Altitude Research Stations Jungfraujoch and Gornergrat (HFSJG). NOAA measurements were supported in part through the NOAA Cooperative Agreement with CIRES (NA17OAR4320101). L.M.W. received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Słodowska-Curie grant agreement no. 101030750. K.E.A. was funded by the UK Natural Environment Research Council through the EnvEast Doctoral Training Partnership (grant number NE/L002582/1). J.C.L. received funding from the ERC project EXC3ITE (EXC3ITE-678904-ERC-2015-STG).

Author information

Authors and Affiliations



L.M.W. and J.C.L. conceived and designed the study. M.K.V., P.B.K., K.E.A., M.C., P.J.F., C.M.H., R.L.L., S.A.M., J.M., S.O’D., D.E.O., S.R., I.V., R.F.W., D.Y. and J.C.L. provided measurement data and analysis. Emissions modelling was designed and performed by L.M.W. and M.R. L.M.W. led the writing of the manuscript with contributions from J.C.L., J.M., M.K.V., K.E.A., I.V., S.R. and M.R., with additional input from all authors.

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Correspondence to Luke M. Western.

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Nature Geoscience thanks Hannah Flerlage, Steve Wofsy, Ross Salawitch and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Primary Handling Editor: Xujia Jiang, in collaboration with the Nature Geoscience team.

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Extended data

Extended Data Fig. 1 Surface dry-air mole fractions and growth rates for CFCs with increasing abundances.

Surface dry-air mole fractions and growth rates are shown for (a) CFC-13, (b) CFC-112a, (c) CFC-113a, (d) CFC-114a and (e) CFC-115 for the available direct atmospheric record (that is, excluding trends derived from firn air) from 1978 through 2020 (1999 through 2020 for CFC-112a). Circles show measured monthly mean mole fractions and lines are the model estimated mole fractions and growth rates, with the colours indicating the semi-hemispheric modelled estimate in which the measurement was made. Uncertainties (1 sd) are shown by the grey shading and are only shown for the global mean mole fractions and growth rates. Details on previously published records can be found in refs. 8,9,17,18. CFC-13 abundances have increased continuously since 1978. The CFC-13 growth rate was rapid in the 1980s, slowed to 0.015 ppt yr−1 in 2000, and subsequently increased over the next two decades. From 2010 to 2020, CFC-13 increased by 9% from 3.04 ppt to 3.31 ppt (3.44 ppt in 2020 using the NOAA record, only available since 2014; see Extended Data Fig. 2). CFC-112a has the lowest abundance of the five CFCs. Its abundance was declining 1999-2006, but rapidly grew from 2010 to 2020 by 19% from 0.066 ppt to 0.078 ppt. The CFC-113a abundance grew since 1978 at a rate less than 0.02 ppt yr−1 until 2010, but from 2010 to 2020 it grew by 141% from 0.43 ppt to 1.02 ppt. CFC-114a growth rates were rapidly accelerating prior to 1990, then dropped to near zero between 1998–2003, after which they accelerated again. Between 2010 and 2020 CFC-114a increased by 9% from 1.03 ppt to 1.13 ppt. Similar to CFC-13 and CFC-114a, CFC-115 abundances also grew rapidly prior to the 1990s, but the timing is different. CFC-115 growth dropped to close to zero between 2005–2011, after which its growth rate again slowly increased. From 2010 to 2020, CFC-115 abundance grew by 4% from 8.38 ppt to 8.71 ppt (growing from 8.42 to 8.75 ppt from 2010 to 2020, or by 4%, using the NOAA record, Extended Data Fig. 2).

Extended Data Fig. 2 Surface dry-air mole fractions for CFC-13 and CFC-115 measured by the NOAA network.

(a) CFC-13 and (b) CFC-115 hemispheric monthly means (circles) and the annual global mean (black line) derived from measurements from the NOAA network. See the caption of Extended Data Fig. 1 for a discussion of these data.

Extended Data Fig. 3 Surface dry-air mole fractions and growth rates for the structural isomers of CFCs.

As Extended Data Fig. 1 but for (a) CFC-112, (b) CFC-113 and (c) CFC-114. CFC-112, CFC-113 and CFC-114 are structural isomers of CFC-112a, CFC-113a and CFC-114a, respectively. Note that the measurement approach at UEA/FJZ can measure the major isomers alone as opposed to the NOAA or AGAGE measurements of these gases (see Methods), where these gases are reported as a sum of the paired isomers. It was previously assumed that the isomers are co-produced and therefore co-emitted into the atmosphere. However, mole fractions of CFC-112 (CCl2FCCl2F) and CFC-113 (CClF2CCl2F) have been declining continuously since 1996, and those of CFC-114 (CClF2CClF2) have declined, or been indistinguishable from zero growth, since 1998.

Extended Data Fig. 4 Annual global mean emissions.

(a) CFC-112, (b) CFC-112a, (c) CFC-113, (d) CFC-113a, (e) CFC-114, (f) CFC-114a, (g) CFC-13 and (h) CFC-115. Shading shows the 1-sigma standard deviation uncertainty. Emissions are in units of gigagrams by mass of the substance released. CFC-113a emissions have grown fastest, with a 244% increase in emissions between 2010–2020 (2.5 ± 0.4 ODP-Gg yr−1 in 2020). Emissions of CFC-112a increased by 169% over the same period, although the 2020 emissions are modest at 0.10 ± 0.03 ODP-Gg yr−1 in 2020, compared to 0.6 ± 0.07 ODP-Gg yr−1 for CFC-114a, which increased by 108%. Emissions of CFC-115 were at a minimum in 2009–2010 (0.1 ± 0.1 ODP-Gg yr−1), before rapidly rising to 0.5 ± 0.1 ODP-Gg yr−1 in 2017, and slightly falling to 0.4 ± 0.1 ODP-Gg yr−1 in 2020 (2010–2020 increase of 192%). CFC-115 emissions are still substantially smaller than at its peak of around 3 ODP-Gg yr−1 in the late 1980s and early 1990s. CFC-13 emissions in 2019 (0.7 ± 0.1 ODP-Gg yr−1) were at their highest of this millennium (0.5 ± 0.1 ODP-Gg yr−1 in 2010 and 0.7 ± 0.1 ODP-Gg yr−1 in 2020), again contrasting with a rapid decline since its emissions peaked in the 1980s, and representing a 41% increase in emissions between 2010–2020.

Extended Data Fig. 5 Comparison of HFC production and CFC emissions which may be associated with HFC production.

The production of HFC-125 (a) and HFC-134a (b) is shown by the blue shading for Article 5 countries and orange shading for non-Article 5 countries. The composite of these two shading blocks shows total global production (without any metric of uncertainty). The estimates of HFC production assumes that all countries have ratified the Kigali Amendment, which to date would underestimate HFC production, and the values displayed are the mean of the lower and upper estimates from ref. 14. The production quantity is shown on the left axis. Mean global emissions are shown for CFC-115 (pink), CFC-113a (green) and CFC-114a (dark orange) by dotted lines and the shading around the line shows the 1-sigma standard deviation uncertainties in the emissions. The right axis displays the emission values for CFCs by mass. CFC-113a, CFC-114a and CFC-115 are known by-products of HFC-125 production (panel a), and CFC-113a and CFC-114a are a feedstock and intermediate, respectively, in one of the production pathways to HFC-134a (panel b).

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Western, L.M., Vollmer, M.K., Krummel, P.B. et al. Global increase of ozone-depleting chlorofluorocarbons from 2010 to 2020. Nat. Geosci. 16, 309–313 (2023).

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