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Fingerprinting the recovery of Antarctic ozone

Abstract

The Antarctic ozone ‘hole’ was discovered in 1985 (ref. 1) and man-made ozone-depleting substances (ODSs) are its primary cause2. Following reductions of ODSs under the Montreal Protocol3, signs of ozone recovery have been reported, based largely on observations and broad yet compelling model–data comparisons4. Although such approaches are highly valuable, they do not provide rigorous statistical detection of the temporal and spatial structure of Antarctic ozone recovery in the presence of internal climate variability. Here we apply pattern-based detection and attribution methods as used in climate-change studies5,6,7,8,9,10,11 to separate anthropogenically forced ozone responses from internal variability, relying on trend pattern information as a function of month and height. The analysis uses satellite observations together with single-model and multi-model ensemble simulations to identify and quantify the month–height Antarctic ozone recovery ‘fingerprint’12. We demonstrate that the data and simulations show compelling agreement in the fingerprint pattern of the ozone response to decreasing ODSs since 2005. We also show that ODS forcing has enhanced ozone internal variability during the austral spring, influencing detection of forced responses and their time of emergence. Our results provide robust statistical and physical evidence that actions taken under the Montreal Protocol to reduce ODSs are indeed resulting in the beginning of Antarctic ozone recovery, defined as increases in ozone consistent with expected month–height patterns.

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Fig. 1: Month–height patterns of ozone trends in observations and simulations.
Fig. 2: Ozone variability modulated by external forcing.
Fig. 3: The local S/N pattern of ozone changes.
Fig. 4: S/N characteristics for the overall month–height fingerprint pattern.

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Data availability

MLS and OMI satellite data are publicly available at https://disc.gsfc.nasa.gov. CCMI model outputs are available at https://archive.ceda.ac.uk and the CESM model outputs are available at https://www.earthsystemgrid.org. All of the pre-processed model data (for example, monthly mean ozone averaged over 66° S–82° S from the CCMI and the WACCM and interpolated onto the MLS vertical coordinates) are available at Zenodo (https://doi.org/10.5281/zenodo.14497873)57.

Code availability

The code used to generate all of the figures in this analysis is available at Zenodo (https://doi.org/10.5281/zenodo.14497873)57.

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Acknowledgements

We thank C. Deser and P. Lin for helpful discussions. We also thank L. Horowitz and M. Lin for providing GFDL model data for this analysis. S.S. and P.W. gratefully acknowledge support from the Atmospheric Chemistry division of the National Science Foundation under grant nos. 2316980 and 2128617. B.D.S. was supported by the Francis E. Fowler IV Center for Ocean and Climate at Woods Hole Oceanographic Institution (WHOI). D.E.K. was financed in part by NASA grant 80NSSC19K0952. Q.F. was supported in part by NSF grant AGS-2202812. The Community Earth System Model (CESM) project is supported by the National Science Foundation and the Office of Science of the U.S. Department of Energy. We gratefully acknowledge high-performance computing support from Cheyenne (https://doi.org/10.5065/D6RX99HX) provided by NCAR’s Computational and Information Systems Laboratory (CISL), sponsored by the National Science Foundation. Work at the Jet Propulsion Laboratory, California Institute of Technology, was carried out under a contract with the National Aeronautics and Space Administration (NASA; 80NM0018D0004).

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Contributions

P.W., S.S. and B.D.S. designed the study. D.E.K. designed and performed the WACCM simulations. P.W. analysed the data and produced the figures. P.W. and S.S. drafted the initial text. B.D.S., Q.F., K.A.S., J.Z., G.L.M. and L.F.M. contributed substantially to the interpretation of findings.

Corresponding authors

Correspondence to Peidong Wang or Susan Solomon.

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Extended data figures and tables

Extended Data Fig. 1 Variability superimposed on external forcing.

Ozone trends from 2005–2018 in individual WACCM realizations (top two rows, with the realization number indicated in the title of each panel) and in individual models from the CCMI-1 (last four rows, with model names indicated in the title of each panel) under the refC2 scenario. The MLS observed trend is shown in the bottom-right panel.

Extended Data Fig. 2 Ozone trends owing to different forcings.

Ensemble-mean ozone trends (2005–2018) averaged over ten WACCM members for each scenario. Results indicate the forced responses in ozone owing to: combined time-evolving GHG and ODS forcing (refC2) (a), evolving GHG forcing only (fODS) (b) and evolving ODS forcing only (fGHG) (c). A detailed description of each scenario is given in Methods. The observed ozone trend from the MLS in 2005–2018 is also shown in panel d for visual comparison with forced ozone trends owing to different forcings.

Extended Data Fig. 3 Ozone variability modulated by external forcing.

Similar to Fig. 2 but for the CCMI models. Note that the spread in ozone trends in the CCMI arises not only from internal variability but also from cross-model differences and errors (discussed in detail in Methods). This convolving of internal variability with model differences and errors contributes to the larger noise in panel a compared with the noise derived from the WACCM single-model refC2 ensemble in Fig. 2b.

Extended Data Fig. 4 The local S/N characteristics of ozone changes.

Similar to Fig. 3 but with results for the CCMI models.

Extended Data Fig. 5 The local S/N pattern of ozone changes.

Similar to Fig. 3 but for signal and noise estimates based on ozone trends over 2005–2023 (rather than over 2005–2018). There is a marked decrease in the MLS ozone in October and November in the mid-stratosphere and in January to May in the lowermost stratosphere. This raises the question of whether these two features may be linked. The bottom panel shows the time series of ozone mixing ratios from the MLS in October at 12.1 hPa (blue) and in February at 82.5 hPa (orange). The decrease in February at 82.5 hPa is mainly because of continued low ozone after 2021 (panel c), which lags the behaviour in October by about a season, suggesting that they may be linked.

Extended Data Fig. 6 Time of emergence of springtime TCO recovery.

Similar to the top and bottom panels in Fig. 3 except the trends are the TCO from the WACCM and the OMI.

Extended Data Fig. 7 Map of the MLS ozone anomalies and polar vortex in October at 12.1 hPa.

The colour shadings indicate the ozone anomaly relative to the zonal mean in 2005–2018. Because the location of the polar vortex can vary considerably over time, dotted markers indicate that the polar vortex has occupied a given grid box for more than 25% of the time in that month. Black dashed lines encompass the area between latitudes 66° S and 82° S.

Extended Data Fig. 8 MLS springtime ozone trends (2005–2018) using fixed latitude averages versus vortex averages.

Monthly mean ozone trends in September, October and November from 2005 to 2018 are shown as blue lines (in which ozone is averaged across fixed latitudes between 66° S and 82° S) and red lines (in which ozone is averaged inside the polar vortex) at different pressure levels. A detailed description of the vortex calculation is provided in Methods. Dots and crosses indicate trends significant at the 5% and 10% levels, respectively. Note that the statistical confidence in this figure is based solely on P-values from linear regression. It does not rely on internal variability noise generated by the WACCM or the CCMI model, as shown in the other figures.

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Wang, P., Solomon, S., Santer, B.D. et al. Fingerprinting the recovery of Antarctic ozone. Nature 639, 646–651 (2025). https://doi.org/10.1038/s41586-025-08640-9

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