Articles | Volume 18, issue 11
Atmos. Chem. Phys., 18, 8409–8438, 2018

Special issue: Chemistry–Climate Modelling Initiative (CCMI) (ACP/AMT/ESSD/GMD...

Atmos. Chem. Phys., 18, 8409–8438, 2018
Research article
 | Highlight paper
15 Jun 2018
Research article  | Highlight paper | 15 Jun 2018

Estimates of ozone return dates from Chemistry-Climate Model Initiative simulations

Sandip S. Dhomse1, Douglas Kinnison2, Martyn P. Chipperfield1,3, Ross J. Salawitch4,5,6, Irene Cionni7, Michaela I. Hegglin8, N. Luke Abraham9,10, Hideharu Akiyoshi11, Alex T. Archibald9,10, Ewa M. Bednarz9, Slimane Bekki12, Peter Braesicke13, Neal Butchart14, Martin Dameris15, Makoto Deushi16, Stacey Frith17,18, Steven C. Hardiman14, Birgit Hassler15, Larry W. Horowitz19, Rong-Ming Hu12, Patrick Jöckel15, Beatrice Josse20, Oliver Kirner21, Stefanie Kremser22, Ulrike Langematz23, Jared Lewis22, Marion Marchand12, Meiyun Lin19,24, Eva Mancini25, Virginie Marécal20, Martine Michou20, Olaf Morgenstern26, Fiona M. O'Connor14, Luke Oman18, Giovanni Pitari27, David A. Plummer28, John A. Pyle9,10, Laura E. Revell22,29, Eugene Rozanov29,30, Robyn Schofield31,32, Andrea Stenke29, Kane Stone31,32,a, Kengo Sudo33,34, Simone Tilmes2, Daniele Visioni25, Yousuke Yamashita11,34, and Guang Zeng26 Sandip S. Dhomse et al.
  • 1School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
  • 2National Center for Atmospheric Research (NCAR), Boulder, Colorado, USA
  • 3National Centre for Earth Observation, University of Leeds, Leeds, LS2 9JT, UK
  • 4Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland, USA
  • 5Department of Atmospheric and Oceanic Science, University of Maryland, College Park, Maryland, USA
  • 6Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland, USA
  • 7Agenzia Nazionale per le Nuove Tecnologie, l'energia e lo Sviluppo Economica Sostenible (ENEA), Bologna, Italy
  • 8Department of Meteorology, University of Reading, Reading, UK
  • 9Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK
  • 10National Centre for Atmospheric Science, Cambridge, UK
  • 11National Institute for Environmental Studies (NIES), Tsukuba, 305-8506, Japan
  • 12IPSL/CNRS, 75252 Paris, France
  • 13IMK-ASF, KIT, Karlsruhe, Germany
  • 14Met Office Hadley Centre, Exeter, UK
  • 15Deutsches Zentrum fur Luft- und Raumfahrt (DLR), Institut fur Physik der Atmosphare, Oberpfaffenhofen, Germany
  • 16Meteorological Research Institute (MRI), Tsukuba, Japan
  • 17Science Systems and Applications, Inc., Lanham, MD, USA
  • 18NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
  • 19NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ 08540, USA
  • 20Meteo-France, Toulouse, France
  • 21Steinbuch Centre for Computing (SCC), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
  • 22Bodeker Scientific, Alexandra, New Zealand
  • 23Institut für Meteorologie, Freie Universitat Berlin, Berlin, Germany
  • 24Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ 08540, USA
  • 25Dept. of Physical and Chemical Sciences and Center of Excellence CETEMPS, Università dell'Aquila, 67100 L'Aquila, Italy
  • 26National Institute of Water and Atmospheric Research (NIWA), Wellington, New Zealand
  • 27Dept. of Physical and Chemical Sciences, Università dell'Aquila, 67100 L'Aquila, Italy
  • 28Climate Research Division, Environment and Climate Change Canada, Montreal, Canada
  • 29ETH Zurich, Institute for Atmospheric and Climate Science, Zurich, Switzerland
  • 30Physikalisch-Meteorologisches Observatorium Davos World Radiation Centre, Davos Dorf, Switzerland
  • 31School of Earth Sciences, University of Melbourne, Melbourne, Australia
  • 32ARC Centre of Excellence for Climate System Science, Sydney, Australia
  • 33Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
  • 34Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, 236-0001, Japan
  • anow at: Massachusetts Institute of Technology (MIT), Boston, Massachusetts, USA

Abstract. >We analyse simulations performed for the Chemistry-Climate Model Initiative (CCMI) to estimate the return dates of the stratospheric ozone layer from depletion caused by anthropogenic stratospheric chlorine and bromine. We consider a total of 155 simulations from 20 models, including a range of sensitivity studies which examine the impact of climate change on ozone recovery. For the control simulations (unconstrained by nudging towards analysed meteorology) there is a large spread (±20 DU in the global average) in the predictions of the absolute ozone column. Therefore, the model results need to be adjusted for biases against historical data. Also, the interannual variability in the model results need to be smoothed in order to provide a reasonably narrow estimate of the range of ozone return dates. Consistent with previous studies, but here for a Representative Concentration Pathway (RCP) of 6.0, these new CCMI simulations project that global total column ozone will return to 1980 values in 2049 (with a 1σ uncertainty of 2043–2055). At Southern Hemisphere mid-latitudes column ozone is projected to return to 1980 values in 2045 (2039–2050), and at Northern Hemisphere mid-latitudes in 2032 (2020–2044). In the polar regions, the return dates are 2060 (2055–2066) in the Antarctic in October and 2034 (2025–2043) in the Arctic in March. The earlier return dates in the Northern Hemisphere reflect the larger sensitivity to dynamical changes. Our estimates of return dates are later than those presented in the 2014 Ozone Assessment by approximately 5–17 years, depending on the region, with the previous best estimates often falling outside of our uncertainty range. In the tropics only around half the models predict a return of ozone to 1980 values, around 2040, while the other half do not reach the 1980 value. All models show a negative trend in tropical total column ozone towards the end of the 21st century. The CCMI models generally agree in their simulation of the time evolution of stratospheric chlorine and bromine, which are the main drivers of ozone loss and recovery. However, there are a few outliers which show that the multi-model mean results for ozone recovery are not as tightly constrained as possible. Throughout the stratosphere the spread of ozone return dates to 1980 values between models tends to correlate with the spread of the return of inorganic chlorine to 1980 values. In the upper stratosphere, greenhouse gas-induced cooling speeds up the return by about 10–20 years. In the lower stratosphere, and for the column, there is a more direct link in the timing of the return dates of ozone and chlorine, especially for the large Antarctic depletion. Comparisons of total column ozone between the models is affected by different predictions of the evolution of tropospheric ozone within the same scenario, presumably due to differing treatment of tropospheric chemistry. Therefore, for many scenarios, clear conclusions can only be drawn for stratospheric ozone columns rather than the total column. As noted by previous studies, the timing of ozone recovery is affected by the evolution of N2O and CH4. However, quantifying the effect in the simulations analysed here is limited by the few realisations available for these experiments compared to internal model variability. The large increase in N2O given in RCP 6.0 extends the ozone return globally by ∼ 15 years relative to N2O fixed at 1960 abundances, mainly because it allows tropical column ozone to be depleted. The effect in extratropical latitudes is much smaller. The large increase in CH4 given in the RCP 8.5 scenario compared to RCP 6.0 also lengthens ozone return by ∼ 15 years, again mainly through its impact in the tropics. Overall, our estimates of ozone return dates are uncertain due to both uncertainties in future scenarios, in particular those of greenhouse gases, and uncertainties in models. The scenario uncertainty is small in the short term but increases with time, and becomes large by the end of the century. There are still some model–model differences related to well-known processes which affect ozone recovery. Efforts need to continue to ensure that models used for assessment purposes accurately represent stratospheric chemistry and the prescribed scenarios of ozone-depleting substances, and only those models are used to calculate return dates. For future assessments of single forcing or combined effects of CO2, CH4, and N2O on the stratospheric column ozone return dates, this work suggests that it is more important to have multi-member (at least three) ensembles for each scenario from every established participating model, rather than a large number of individual models.

Short summary
We analyse simulations from the Chemistry-Climate Model Initiative (CCMI) to estimate the return dates of the stratospheric ozone layer from depletion by anthropogenic chlorine and bromine. The simulations from 20 models project that global column ozone will return to 1980 values in 2047 (uncertainty range 2042–2052). Return dates in other regions vary depending on factors related to climate change and importance of chlorine and bromine. Column ozone in the tropics may continue to decline.
Final-revised paper