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Integrated ozone depletion as a metric for ozone recovery


The Montreal Protocol is successfully protecting the ozone layer. The main halogen gases responsible for stratospheric ozone depletion have been regulated under the Protocol, their combined atmospheric abundances are declining and ozone is increasing in some parts of the atmosphere1. Ozone depletion potentials2,3,4, relative measures of compounds’ abilities to deplete stratospheric ozone, have been a key regulatory component of the Protocol in successfully guiding the phasing out in the manufacture of the most highly depleting substances. However, this latest, recovery phase in monitoring the success of the Protocol calls for further metrics. The ‘delay in ozone return’ has been widely used to indicate the effect of different emissions or phase-down strategies, but we argue here that it can sometimes be ambiguous or even of no use. Instead, we propose the use of an integrated ozone depletion (IOD) metric to indicate the impact of any new emission. The IOD measures the time-integrated column ozone depletion and depends only on the emission strength and the whole atmosphere and stratospheric lifetimes of the species considered. It provides a useful complementary metric of the impact of specific emissions of an ozone depleting substance for both the scientific and policy communities.

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Fig. 1: A schematic of ozone recovery under different halogen emission scenarios based on CCM calculations.
Fig. 2: Total column ozone trajectories calculated in our CCM.
Fig. 3: Relationship between IOD, total halogen emissions and the stratospheric and whole atmosphere lifetimes.

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Data availability

The simulation data used in this study are archived in the UKCA group workspace on the JASMIN platform ( maintained by the Centre for Environmental Data Analysis and are available on reasonable request from the corresponding authors. Source data are provided with this paper.

Code availability

The UM-UKCA model is available for use under licence. Several research organizations and national meteorological services use the UM in collaboration with the Met Office to undertake basic atmospheric process research, produce forecasts, develop the UM code and build and evaluate Earth system models. For further information on how to apply for a licence see (last accessed 27 September 2021).


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J.A.P, J.K., N.L.A. and P.T.G. were financially supported by NERC through NCAS (grant no. R8/H12/83/003). M.P.C. was supported by NERC through the grant nos. NE/R001782/1 (SISLAC) and NE/V011863/1 (LSO3). Model simulations have been performed using the ARCHER UK National Supercomputing Service. This work used the UK Research Data Facility (, last accessed 2 June 2021). This work used JASMIN, the UK collaborative data analysis facility.

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Authors and Affiliations



J.A.P. proposed the initial study, which was developed jointly by J.K., J.A.P. and M.P.C. J.K. performed most of the calculations with support from N.L.A. and P.T.G. J.A.P. and J.K. led the writing to which all authors contributed.

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Correspondence to John A. Pyle or James Keeble.

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Nature thanks the anonymous reviewers for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 Time series, from 1960 to 2100, of total column ozone (TCO, DU), averaged from 90°S-90°N, from the simulations analysed in this study.

Part a) plots annual mean model data and b) plots the data after it has been smoothed using an 11-point boxcar smoothing, following Dhomse et al34. The large difference at 2100 between Base and the scenario with 30-year emissions of CFC-11 and CFC-12 arises from the large increase in (and subsequent emission from) their banks, assumed in that scenario (as discussed in Keeble et al.25).

Extended Data Fig. 2 Integrated ozone depletion (IOD, in DU years) from all UM-UKCA integrations plotted against the total halogen emission in Tg Cl, EEq, multiplied by the whole atmosphere lifetime of the emitted species divided by its stratospheric lifetime, for comparison with Figure 3.

The IOD for short-lived gases is calculated over the perturbation period as defined in the text, otherwise as in Figure 3. The correlation coefficient, r, is now 0.90, and when the scenario with the emission of CFC-11 and CFC-12 is not included, the correlation coefficient remains high (0.83).

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Pyle, J.A., Keeble, J., Abraham, N.L. et al. Integrated ozone depletion as a metric for ozone recovery. Nature 608, 719–723 (2022).

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