Multi-model assessment of stratospheric ozone return dates and ozone recovery in CCMVal-2 models
Authors: Eyring V. , Cionni I. , Bodeker G. E. , Charlton-Perez A. J. , Kinnison D. E. , Scinocca J. F. , Waugh D. W. , Akiyoshi H. , Bekki S. , Chipperfield M. P. , Dameris M. , Dhomse S. , Frith S. M. , Garny H. , Gettelman A. , Kubin A. , Langematz U. , Mancini E. , Marchand M. , Nakamura T. , Oman L. D. , Pawson S. , Pitari G. , Plummer D. A. , Rozanov E. , Shepherd T. G. , Shibata K. , Tian W. , Braesicke P. , Hardiman S. C. , Lamarque J. F. , Morgenstern O. , Pyle J. A. , Smale D. , Yamashita Y. 
Published: May 2010

Abstract. Projections of stratospheric ozone from a suite of chemistry-climate models (CCMs) have been analyzed. In addition to a reference simulation where anthropogenic halogenated ozone depleting substances (ODSs) and greenhouse gases (GHGs) vary with time, sensitivity simulations with either ODSs or GHGs concentrations fixed at 1960 levels were performed to disaggregate the drivers of projected ozone changes. These simulations were also used to assess the two distinct milestones of ozone returning to historical values (ozone return dates) and ozone no longer being influenced by ODSs (full ozone recovery). These two milestones are different. The date of ozone returning to historical values does not indicate complete recovery from ODSs in most cases, because GHG induced changes accelerate or decelerate ozone changes in many regions. In the upper stratosphere where GHG induced stratospheric cooling increases ozone, full ozone recovery has not likely occurred by 2100 while ozone returns to its 1980 or even 1960 levels well before (~2025 and 2040, respectively). In contrast, in the tropical lower stratosphere ozone decreases continuously from 1960 to 2100 due to projected increases in tropical upwelling, while by around 2040 it is already very likely that full recovery from the effects of ODSs has occurred, although ODS concentrations are still elevated by this date. In the lower midlatitude stratosphere the evolution differs from that in the tropics, and rather than a steady decrease of ozone, first a decrease of ozone is simulated between 1960 and 2000, which is then followed by a steady increase throughout the 21st century. Ozone in the lower stratosphere midlatitudes returns to its 1980 levels ${\\sim}$2045 in the NH and ~2055 in the SH, and full ozone recovery is likely reached by 2100 in both hemispheres. Overall, in all regions except the tropical lower stratosphere, full ozone recovery from ODSs occurs significantly later than the return of total column ozone to its 1980 level. The latest return of total column ozone is projected to occur over Antarctica (~2050–2060) whereas it is not likely that full ozone recovery is reached by the end of the 21st century in this region. Arctic total column ozone is projected to return to 1980 levels well before Cly does so (~2020–2030) and while it is likely that full recovery of ozone from the effects of ODSs has occurred by ~2035, at no time before 2100 is it very likely that full recovery has occurred. In contrast to the Antarctic, by 2100 Arctic total column ozone is projected to be above 1960 levels, but not in the fixed GHG simulation, indicating that climate change plays a significant role.