On the attribution of stratospheric ozone and temperature changes to changes in ozone-depleting substances and well-mixed greenhouse gases

• Published in: Atmospheric chemistry and physics discussions Vol. 7; no. 4; pp. 12327 - 12347
• Main Authors: Shepherd, T G, Jonsson, AI
• Format: Journal Article
• Language: English
• Published: European Geosciences Union 21.08.2007
• Subjects: Ocean, Atmosphere; Sciences of the Universe
• ISSN: 1680-7367

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 CO sub(2) increases. However, CO sub(2)-induced cooling alters ozone abundance by perturbing ozone chemistry, thereby coupling the stratospheric ozone-temperature response to changes in CO sub(2) and ozone-depleting substances (ODSs). Here we untangle the ozone-temperature coupling and show that the attribution of global-mean stratospheric temperature changes to CO sub(2) and ODS changes (which are the true anthropogenic forcing agents) can be quite different from the traditional attribution to CO sub(2) 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 CO sub(2), and the CO sub(2)-induced cooling in the upper stratosphere has been somewhat overestimated. When considering ozone recovery, however, the ozone-temperature coupling is a first-order effect; fully 2/5 of the upper stratospheric ozone increase projected to occur from 2010-2040 is attributable to CO sub(2) increases. Thus, it has now become necessary to base attribution of global-mean stratospheric temperature changes on CO sub(2) and ODS changes rather than on CO sub(2) and ozone changes.