Atmos. Chem. Phys. Discuss., 12, 26047-26097, 2012
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Tropospheric ozone changes, radiative forcing and attribution to emissions in the Atmospheric Chemistry and Climate Model Inter-comparison Project (ACCMIP)
D. S. Stevenson1, P. J. Young2,3, V. Naik4, J.-F. Lamarque5, D. T. Shindell6, A. Voulgarakis7, R. B. Skeie8, S. B. Dalsoren8, G. Myhre8, T. K. Berntsen8, G. A. Folberth9, S. T. Rumbold9, W. J. Collins9, I. A. MacKenzie1, R. M. Doherty1, G. Zeng10, T. P. C. van Noije11, A. Strunk11, D. Bergmann12, P. Cameron-Smith12, D. A. Plummer13, S. A. Strode14, L. Horowitz15, Y. H. Lee6, S. Szopa16, K. Sudo17, T. Nagashima18, B. Josse19, I. Cionni20, M. Righi21, V. Eyring21, A. Conley5, K. W. Bowman22, and O. Wild23
1School of GeoSciences, The University of Edinburgh, Edinburgh, UK
2Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, Colorado, USA
3Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, Colorado, USA
4UCAR/NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA
5National Center for Atmospheric Research, Boulder, Colorado, USA
6NASA Goddard Institute for Space Studies and Columbia Earth Institute, New York, NY, USA
7Department of Physics, Imperial College London, London, UK
8CICERO, Center for International Climate and Environmental Research-Oslo, Oslo, Norway
9Met Office Hadley Centre, Exeter, UK
10National Institute of Water and Atmospheric Research, Lauder, New Zealand
11Royal Netherlands Meteorological Institute, De Bilt, The Netherlands
12Lawrence Livermore National Laboratory, Livermore, California, USA
13Canadian Centre for Climate Modeling and Analysis, Environment Canada, Victoria, British Columbia, Canada
14NASA Goddard Space Flight Centre, Greenbelt, Maryland, USA and Universities Space Research Association, Columbia, MD, USA
15NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA
16Laboratoire des Sciences du Climat et de l'Environment, Gif-sur-Yvette, France
17Department of Earth and Environmental Science, Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
18National Institute for Environmental Studies, Tsukuba-shi, Ibaraki, Japan
19GAME/CNRM, Météo-France, CNRS – Centre National de Recherches Météorologiques, Toulouse, France
20Agenzia Nazionale per le Nuove Tecnologie, l'energia e lo Sviluppo Economico Sostenibile (ENEA), Bologna, Italy
21Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
22NASA Jet Propulsion Laboratory, Pasadena, California, USA
23Lancaster Environment Centre, University of Lancaster, Lancaster, UK

Abstract. Ozone (O3) from 17 atmospheric chemistry models taking part in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) has been used to calculate tropospheric ozone radiative forcings (RFs). We calculate a~value for the pre-industrial (1750) to present-day (2010) tropospheric ozone RF of 0.40 W m−2. The model range of pre-industrial to present-day changes in O3 produces a spread (±1 standard deviation) in RFs of ±17%. Three different radiation schemes were used – we find differences in RFs between schemes (for the same ozone fields) of ±10%. Applying two different tropopause definitions gives differences in RFs of ±3%. Given additional (unquantified) uncertainties associated with emissions, climate-chemistry interactions and land-use change, we estimate an overall uncertainty of ±30% for the tropospheric ozone RF. Experiments carried out by a subset of six models attribute tropospheric ozone RF to increased emissions of methane (47%), nitrogen oxides (29%), carbon monoxide (15%) and non-methane volatile organic compounds (9%); earlier studies attributed more of the tropospheric ozone RF to methane and less to nitrogen oxides. Normalising RFs to changes in tropospheric column ozone, we find a global mean normalised RF of 0.042 W m−2 DU−1, a value similar to previous work. Using normalised RFs and future tropospheric column ozone projections we calculate future tropospheric ozone RFs (W m−2; relative to 1850 – add 0.04 W m−2 to make relative to 1750) for the Representative Concentration Pathways in 2030 (2100) of: RCP2.6: 0.31 (0.16); RCP4.5: 0.38 (0.26); RCP6.0: 0.33 (0.24); and RCP8.5: 0.42 (0.56). Models show some coherent responses of ozone to climate change: decreases in the tropical lower troposphere, associated with increases in water vapour; and increases in the sub-tropical to mid-latitude upper troposphere, associated with increases in lightning and stratosphere-to-troposphere transport.

Citation: Stevenson, D. S., Young, P. J., Naik, V., Lamarque, J.-F., Shindell, D. T., Voulgarakis, A., Skeie, R. B., Dalsoren, S. B., Myhre, G., Berntsen, T. K., Folberth, G. A., Rumbold, S. T., Collins, W. J., MacKenzie, I. A., Doherty, R. M., Zeng, G., van Noije, T. P. C., Strunk, A., Bergmann, D., Cameron-Smith, P., Plummer, D. A., Strode, S. A., Horowitz, L., Lee, Y. H., Szopa, S., Sudo, K., Nagashima, T., Josse, B., Cionni, I., Righi, M., Eyring, V., Conley, A., Bowman, K. W., and Wild, O.: Tropospheric ozone changes, radiative forcing and attribution to emissions in the Atmospheric Chemistry and Climate Model Inter-comparison Project (ACCMIP), Atmos. Chem. Phys. Discuss., 12, 26047-26097, doi:10.5194/acpd-12-26047-2012, 2012.
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