EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Evaluating stratospheric ozone and water vapor changes in CMIP6 models from 1850-2100 

James Keeble1, Birgit Hassler2, Antara Banerjee3, Ramiro Checa-Garcia4, Gabriel Chiodo5, Sean Davis4, Veronika Eyring2, Paul Griffiths1, Olaf Morgenstern6, Peer Nowack7, Guang Zeng6, and Jiankai Zhang8
James Keeble et al.
  • 1University of Cambridge, Department of Chemistry, Cambridge, United Kingdom of Great Britain – England, Scotland, Wales (
  • 2Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 3NOAA Earth System Research Laboratory Chemical Sciences Division, Boulder, CO, USA
  • 4Laboratoire des sciences du climat et de l'environnement: Gif-sur-Yvette, Île-de-France, France
  • 5Department of Environmental Systems Science, Swiss Federal Institute of Technology, Zurich, Switzerland
  • 6National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand
  • 7Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, UK
  • 8Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou, 730000, Gansu, China

Stratospheric ozone and water vapor are key components of the Earth system, and past and future changes to both have important impacts on global and regional climate. Here we evaluate long-term changes in these species from the pre-industrial (1850) to the end of the 21st century in CMIP6 models under a range of future emissions scenarios. There is good agreement between the CMIP multi-model mean and observations for total column ozone (TCO), although there is substantial variation between the individual CMIP6 models. For the CMIP6 multi-model mean, global mean TCO has increased from ~300 DU in 1850 to ~305 DU in 1960, before rapidly declining in the 1970s and 1980s following the use and emission of halogenated ozone depleting substances (ODSs). TCO is projected to return to 1960’s values by the middle of the 21st century under the SSP2-4.5, SSP3-7.0, SSP4-3.4, SSP4-6.0 and SSP5-8.5 scenarios, and under the SSP3-7.0 and SSP5-8.5 scenarios TCO values are projected to be ~10 DU higher than the 1960’s values by 2100. However, under the SSP1-1.9 and SSP1-1.6 scenarios, TCO is not projected to return to the 1960’s values despite reductions in halogenated ODSs due to decreases in tropospheric ozone mixing ratios. This global pattern is similar to regional patterns, except in the tropics where TCO under most scenarios is not projected to return to 1960’s values, either through reductions in tropospheric ozone under SSP1-1.9 and SSP1-2.6, or through reductions in lower stratospheric ozone resulting from an acceleration of the Brewer-Dobson Circulation under other SSPs. In contrast to TCO, there is poorer agreement between the CMIP6 multi-model mean and observed lower stratospheric water vapour mixing ratios, with the CMIP6 multi-model mean underestimating observed water vapour mixing ratios by ~0.5 ppmv at 70hPa. CMIP6 multi-model mean stratospheric water vapor mixing ratios in the tropical lower stratosphere have increased by ~0.5 ppmv from the pre-industrial to the present day and are projected to increase further by the end of the 21st century. The largest increases (~2 ppmv) are simulated under the future scenarios with the highest assumed forcing pathway (e.g. SSP5-8.5). Tropical lower stratospheric water vapor, and to a lesser extent TCO, show large variations following explosive volcanic eruptions.

How to cite: Keeble, J., Hassler, B., Banerjee, A., Checa-Garcia, R., Chiodo, G., Davis, S., Eyring, V., Griffiths, P., Morgenstern, O., Nowack, P., Zeng, G., and Zhang, J.: Evaluating stratospheric ozone and water vapor changes in CMIP6 models from 1850-2100 , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15994,, 2021.


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