Quantitative assessment of Southern Hemisphere ozone in chemistry-climate model simulations
Stratospheric ozone recovery in the Southern Hemisphere is expected to drive pronounced trends in atmo-spheric temperature and circulation from the stratosphere to the troposphere in the 21st century; therefore ozone changes need to be accounted for in future climate simulations. Many climate models do not have interactive ozone chemistry and rely on prescribed ozone fields, which may be obtained from coupled chemistry-climate model (CCM) simulations. How-ever CCMs vary widely in their predictions of ozone evo-lution, complicating the selection of ozone boundary condi-tions for future climate simulations. In order to assess which models might be expected to better simulate future ozone evolution, and thus provide more realistic ozone boundary conditions, we assess the ability of twelve CCMs to simulate observed ozone climatology and trends and rank the models according to their errors averaged across the individual diag-nostics chosen. According to our analysis no one model per-forms better than the others in all the diagnostics; however, combining errors in individual diagnostics into one metric of model performance allows us to objectively rank the mod-els. The multi-model average shows better overall agreement with the observations than any individual model. Based on this analysis we conclude that the multi-model average ozone projection presents the best estimate of future ozone evolu-tion and recommend it for use as a boundary condition in future climate simulations. Our results also demonstrate a sensitivity of the analysis to the choice of reference data set for vertical ozone distribution over the Antarctic, highlight-ing the constraints that large observational uncertainty im-poses on such model verification.