The stratospheric response to changes in ozone and carbon dioxide as modelled with a GCM including parameterised ozone chemistry

Abstract

To disentangle the combined effect of CO2 and O3 changes on both the large-scale circulation and global distribution of ozone, we have conducted four idealised climate change experiments using a version of the Met Office's Unified Model (UM) with a well-resolved middle atmosphere and parameterised stratospheric ozone chemistry, imposing CO2 and ozone changes. Focusing on the northern hemisphere we compare our model results with respect to existing observations of process-oriented quantities involving ozone, in particular the slope of the ozone loss-PSC volume relationship as described by REX et al. (2004). We study the sensitivities in our model system with respect to changes in trace gases and discuss problems in assessing likely future developments relating to the recovery of the ozone layer. We find a highly non-linear response in the modelled ozone at 70 hPa during northern hemisphere winter, whereas the response on the southern hemisphere is quite linear. The ozone loss-PSC volume relationship in the northern hemisphere is well-defined for all integrations, except for the case with the most extreme climate change (doubled CO2 and decreased ozone).