Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 8 5 2008 10.5194/acp-8-1435-2008 http://www.atmos-chem-phys.net/8/1435/2008/ http://www.atmos-chem-phys.net/8/1435/2008/acp-8-1435-2008.html http://www.atmos-chem-phys.net/8/1435/2008/acp-8-1435-2008.pdf 1435 1444 2008-03-12 On the attribution of stratospheric ozone and temperature changes to changes in ozone-depleting substances and well-mixed greenhouse gases T. G. Shepherd tgs@atmosp.physics.utoronto.ca A. I. Jonsson Department of Physics, University of Toronto, 60 St. George Street, Toronto, Ontario, M5S 1A7, Canada The vertical profile of global-mean stratospheric temperature changes has traditionally represented an important diagnostic for the attribution of the cooling effects of stratospheric ozone depletion and CO₂ increases. However, CO₂-induced cooling alters ozone abundance by perturbing ozone chemistry, thereby coupling the stratospheric ozone and temperature responses to changes in CO₂ and ozone-depleting substances (ODSs). Here we untangle the ozone-temperature coupling and show that the attribution of global-mean stratospheric temperature changes to CO₂ and ODS changes (which are the true anthropogenic forcing agents) can be quite different from the traditional attribution to CO₂ and ozone changes. The significance of these effects is quantified empirically using simulations from a three-dimensional chemistry-climate model. The results confirm the essential validity of the traditional approach in attributing changes during the past period of rapid ODS increases, although we find that about 10% of the upper stratospheric ozone decrease from ODS increases over the period 1975–1995 was offset by the increase in CO₂, and the CO₂-induced cooling in the upper stratosphere has been somewhat overestimated. 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