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Discussion papers
https://doi.org/10.5194/acp-2019-734
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-734
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 23 Sep 2019

Submitted as: research article | 23 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Inconsistencies between chemistry climate model and observed lower stratospheric trends since 1998

William T. Ball1,2, Gabriel Chiodo1,3, Marta Abalos4, and Justin Alsing5,6 William T. Ball et al.
  • 1Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology Zurich, Universitaetstrasse 16, CHN, CH-8092 Zurich, Switzerland
  • 2Physikalisch-Meteorologisches Observatorium Davos World Radiation Centre, Dorfstrasse 33, 7260 Davos Dorf, Switzerland
  • 3Department of Applied Physics and Applied Mathematics, 5 Columbia University, New York, NY, USA
  • 4Earth Physics and Astrophysics Dep., Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid, Spain
  • 5Oskar Klein Centre for Cosmoparticle Physics, Stockholm University, Stockholm SE-106 91, Sweden
  • 6Imperial Centre for Inference and Cosmology, Department of Physics, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK

Abstract. The stratospheric ozone layer shields surface life from harmful ultraviolet radiation. Following the Montreal Protocol ban of long-lived ozone depleting substances (ODSs), rapid depletion of total column ozone (TCO) ceased in the late 1990s and ozone above 32 km now enjoys a clear recovery. However, there is still no confirmation of TCO recovery, and evidence has emerged that ongoing quasi-global (60° S–60° N) lower stratospheric ozone decreases may be responsible, dominated by low latitudes (30° S–30° N). Chemistry climate models (CCMs) used to project future changes predict that lower stratospheric ozone will decrease in the tropics by 2100, but not at mid-latitudes (30°–60°). Here, we show that CCMs display an ozone decline similar to that observed in the tropics over 1998–2016, likely driven by a increase of tropical upwelling. On the other hand, mid-latitude lower stratospheric ozone is observed to decrease, while CCMs show an increase. Despite opposing lower stratospheric ozone changes, which should induce opposite temperature trends, CCM and observed temperature trends agree; we demonstrate that opposing model-observation stratospheric water vapour (SWV) trends, and their associated radiative effects, explain why temperature changes agree in spite of opposing ozone trends. We provide new evidence that the observed mid-latitude trends can be explained by enhanced mixing between the tropics and extratropics. We further show that the temperature trends are consistent with the observed mid-latitude ozone decrease. Together, our results suggest that large scale circulation changes expected in the future from increased greenhouse gases (GHGs) may now already be underway, but that most CCMs are not simulating well mid-latitude ozone layer changes. The reason CCMs do not exhibit the observed changes urgently needs to be understood to improve confidence in future projections of the ozone layer.

William T. Ball et al.
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BASIC ozone composite 1998–2018 J. Alsing and W. T. Ball https://doi.org/10.17632/2mgx2xzzpk.3

William T. Ball et al.
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Short summary
Recent lower stratospheric ozone decreases remain unexplained. We show that chemistry climate models are not generally able to reproduce mid-latitude ozone and water vapour changes. Our analysis of observations provides evidence that climate change may be responsible for the ozone trends. While model projections suggest extra-tropical ozone should recover by 2100, our study raises questions about their efficacy to simulate lower stratospheric changes in this region.
Recent lower stratospheric ozone decreases remain unexplained. We show that chemistry climate...
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