1Department of Geosciences, University of Oslo, Oslo, Norway
2Hadley Centre, Met Office, Exeter, Devon, UK
3Climate Change Unit, Joint Research Centre, Climate Change Unit, Ispra, Italy
4Department of Meteorology, University of Reading, Reading, UK
5Institut für Physik der Atmosphäre, DLR, Oberpfaffenhoffen, Germany
6Laboratoire des Sciences du Climat et de L’Environnement (LSCE), Gif-sur-Yvette, France
7Dipartimento di Fisica, Università de L’Aquila, Coppito, L’Aquila, Italy
8Atmospheric Chemistry Division, NCAR, Boulder, Colorado, USA
9Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA
10Earth System Science Department, University of California at Irvine, USA
11Cambridge University, Chemistry Department, Cambridge, UK
12School of Geosciences, University of Edinburgh, Edinburgh, UK
13Frontier Research Center for Global Change, JAMSTEC, Yokohama, Japan
Abstract. Changes in atmospheric ozone have occurred since the preindustrial era as a result of increasing anthropogenic emissions. Within ACCENT, a European Network of Excellence, ozone changes between 1850 and 2000 are assessed for the troposphere and the lower stratosphere (up to 30 km) by a variety of seven chemistry-climate models and three chemical transport models. The modeled ozone changes are taken as input for detailed calculations of radiative forcing.
When only changes in chemistry are considered (constant climate) the modeled global-mean tropospheric ozone column increase since preindustrial times ranges from 7.9 DU to 13.8 DU among the ten participating models, while the stratospheric column reduction lies between 14.1 DU and 47.9 DU in the models considering stratospheric chemistry. The resulting radiative forcing is strongly dependent on the location and altitude of the modeled ozone change and varies between 0.26 Wm−2 and 0.53 Wm−2 due to ozone change in the troposphere and −0.25 Wm−2 and +0.12 Wm−2 due to the stratospheric ozone change.
Changes in ozone and other greenhouse gases since preindustrial times have altered climate. Six out of the ten participating models have performed an additional calculation taking into account both chemical and climate change. The isolated effect of climate change is an enhancement of the tropospheric ozone column increase in all models, ranging from 1% to 37%, while the stratospheric reduction becomes slightly less severe in most models. In the three climate-chemistry models with detailed tropospheric and stratospheric chemistry the inclusion of climate change increases the resulting radiative forcing due to tropospheric ozone change by up to 0.08 Wm−2, while the radiative forcing due to stratospheric ozone change is reduced by up to 0.14 Wm−2.
Considering tropospheric and stratospheric change combined, the total ozone column change is negative while the resulting net radiative forcing is positive.