The Stratospheric response to doubled CO2 in two chemistry-climate models

This study examines the impact of doubling CO₂ on stratospheric dynamics and ozone in two chemistry-climate models. Previous work by these authors, using a climate model with parameterized stratospheric ozone chemistry, found a dependence of northern hemisphere (NH) polar vortex strength on background CO₂ concentration; the polar vortex showed a weakening due to O₃ depletion in present-day conditions, but a strengthening in a double-CO₂ atmosphere. This work is compared with results from the UK Chemistry and Aerosol model (UKCA), a new chemistry-climate model with interactive stratospheric chemistry. Integrating UKCA at both present-day and doubled CO₂ concentrations, small ensembles are constructed by imposing small changes on the initial CO₂ concentrations for each of the ensemble members. The ensemble mean changes in polar vortex strength and ozone concentrations during mid- and late winter, in both hemispheres, are assessed.