Newchurch et al. (2003) were the first to claim to identify ozone recovery in the upper stratosphere. With more years and different satellite data available, it is now clear that after the ozone decline in the upper stratosphere, by 10 to 15%, from the early 1980s to the mid-1990s, the ozone amount has leveled off since then. In the last 10 years, the various records show even signs of an increase (Steinbrecht et al., 2009; Jones et al. 2009; WMO, 2011). This long term behaviour of ozone in the upper stratosphere is thus in agreement with the earlier large increase and subsequent slow decline of the stratospheric halogen load. Particular attention attracted the tropical lowermost stratosphere where ozone trends are mainly driven by the tropical upwelling and not by chemistry (SPARC CCMVal, 2010; Lamarque and Solomon, 2010). Randel and Thompson (2011) confirmed a negative trend from a combination of satellite (SAGE I+II) and ozone sondes (as expected from an increase in tropical upwelling), but noted the uncertainties in the satellite data record particularly in this altitude region. A SPARC/WMO/IO3C initiative on vertical ozone profiles has started in 2011 that attempts to better integrate all available ozone profile data records in order to improve upon the long-term consistency of the multiple datasets.

Atmospheric dynamics play a large role in the observed total ozone trends as dynamical changes (e.g. Brewer-Dobson circulation, BDC) go hand-in-hand with chemical changes in the lower stratosphere (Tegtmeier et al., 2008; Kiesewetter et al., 2010). Despite the large variability in total ozone from year-to-year, evidence of a halogen related rebound of total ozone in both hemispheres has been shown by careful separation of dynamical and chemical factors (Mäder et al., 2010, Salby et al., 2011, Weber et al., 2011). In recent years we have experienced extremes in the inter-annual variability, in particular in the NH, with unusually high ozone in spring 2010 (Steinbrecht et al., 2011) followed by record Arctic ozone loss in the recent winter 2010/11 (Manney et al., 2011, Sinnhuber et al., 2011). The last cold Arctic winter confirms trends observed by Rex et al. (2004) (updated in WMO, 2011), that the PSC volume is increasing in cold Arctic winters. There are two opposite effects expected related to increases in GHG. On the one hand the stratosphere is expected to cool in a changing climate potentially leading to more ozone depletion and on the other hand models predict that the BDC will strengthen (Butchart et al., 2010) and thereby warm the polar stratosphere leading to more ozone transport.

Substantial uncertainties still exist in the total bromine budget and in particular the contribution of very short-lived substances (VSLS) (WMO 2011) and their impact on stratospheric ozone loss in a changing climate (Sinnhuber et al., 2009, WMO 2011). Changes in the background atmosphere (NO₂, HO₂, aerosols) due to the increasingly important role of N₂O (Ravishankara et al., 2009) and CH₄ emissions will change the chemistry feedback in the future. The dynamics-chemistry coupling will, thus, likely undergo modifications as a result of a changing climate and will modify the future ozone return dates as compared to the halogen return date (Waugh et al., 2009; Oman et al., 2009; Eyring et al., 2010).