Evidence of rapid polar ozone depletion and its attribution to chlorine emissions led to the ratification of the Montreal Protocol and now the chlorine loading in the atmosphere is in decline. The future of the polar and non-polar stratospheric ozone layer is however not certain because of the simultaneous effect of the rise in greenhouse gas (GHG) loading. Past studies have shown that the GHG increase may change significantly the thermal structure of the stratosphere and thereby affect ozone chemistry. The focus of this study is the effect of past and projected GHG increases on stratospheric ozone.

Investigations are based upon a new coupled three dimensional chemistry - general circulation model. The newly developed chemistry model FASTOC (FAst STrastospheric Ozone Chemistry) represents the chemistry of stratospheric ozone in terms of constituent relationships derived from an accurate chemical box model. The circulation is performed by the IGCM (Intermediate General Circulation Model) of the University of Reading. This model is used in its T21 version with 26 levels from the surface up to 0.1hPa. The thrust of this coupled model is the combination of a high computational speed and a realistic representation of ozone chemistry.

In this talk, effects of GHG loading on the stratospheric ozone equilibrium will be discussed in the context of time-slice experiments representing pre-industrial, present day and projected GHG conditions.