The release into the atmosphere of CFCs and other halogen-containing chemical species (collectively referred to as ozone depleting substances or ODSs) have had a marked effect on the abundance of ozone in the stratosphere. The iconic images of the Antarctic ozone hole helped galvanize international action to curb the emission of a suite of industrial chemicals that were believed to be responsible for the halogen-driven destruction of ozone in the stratosphere. The results of these actions can now be seen in the continuing decrease in the stratospheric abundance of chlorine and the stabilization of ozone concentrations in the upper stratosphere. Due to the long atmospheric lifetime of ODSs, their concentration will continue to decrease for the rest of the 21 ^st century, a time when the climate of the Earth is expected to undergo significant changes. While the troposphere will warm, the stratosphere will cool and the concentration of species such as CH ₄ and N ₂ O, that play both a role in the radiative balance of the Earth and the chemistry of the atmosphere, are expected to change.

To understand how these different factors will interact and determine the future evolution of the ozone layer, the Canadian Middle Atmosphere Model (CMAM) was used to simulate the changing climate and chemistry of the atmosphere until the end of the 21 ^st century. Simulations were made with different combinations of forcings either held constant or allowed to vary following a pre-defined future scenario. The differences that develop between the simulations are then analysed to quantify the effects of the different forcings on the projected changes in stratospheric ozone.

Results from this completed study will be presented along with some on-going work with a more recent version of CMAM that includes a more robust description of the chemistry of the troposphere.