In these models, the assumption is made that during the 21st century, stratospheric ozone will slowly recover toward pre-industrial values due to the reduction of anthropogenic halogens (Miller et al. (2006)). The exception is CCCma where volcanic and ozone forcing are not included for both PD and GHG intervals. It should be noted that recent changes of Antarctic climate have been linked to modifications of the anthropogenic forcing associated to GHG emission, as well as to stratospheric ozone. For instance, Cai and Cowan (2007) demonstrated that climate simulations that contain time-variable stratospheric ozone forcing produced an averaged trend for the Southern Hemisphere Annular Mode (SAM) that is comparable to the trend from NNR for the late-20th century. Therefore, results presented here may be tightly related to the model treatment of the GHG forcing in particular to the coupling between the troposphere and the lower stratosphere (e.g. Kushner et al. (2001)).
Since the IPCC models investigated here vary in horizontal resolution (from 1.4° to 3.75°, Table I), the results presented have been interpolated to a 1° × 1° grid by applying OACRES (Objective Analysis using the CRESsman scheme (Cressman (1959)). Multiple passes are made through the grid with increasingly smaller radii of influence. At each pass, a new value is calculated for each grid point based on a correction factor that is determined by looking at each original grid within the radius of influence. For each such grid, an error is defined as the difference between the grid value and the value from interpolation. The correction factor is based on a distance weighted formula applied to all such errors within the radius of influence. The correction factors are applied to each grid point before the next pass is made.