Atmos. Chem. Phys., 13, 5277-5298, 2013
www.atmos-chem-phys.net/13/5277/2013/
doi:10.5194/acp-13-5277-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Preindustrial to present-day changes in tropospheric hydroxyl radical and methane lifetime from the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)
V. Naik1, A. Voulgarakis2, A. M. Fiore3, L. W. Horowitz4, J.-F. Lamarque5, M. Lin4,6, M. J. Prather7, P. J. Young8,9,*, D. Bergmann10, P. J. Cameron-Smith10, I. Cionni11, W. J. Collins12,**, S. B. Dalsøren13, R. Doherty14, V. Eyring15, G. Faluvegi16, G. A. Folberth12, B. Josse17, Y. H. Lee16, I. A. MacKenzie14, T. Nagashima18, T. P. C. van Noije19, D. A. Plummer20, M. Righi15, S. T. Rumbold12, R. Skeie13, D. T. Shindell16, D. S. Stevenson14, S. Strode21, K. Sudo22, S. Szopa23, and G. Zeng24
1UCAR/NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA
2Department of Physics, Imperial College, London, UK
3Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York, USA
4NOAA Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA
5National Center for Atmospheric Research, Boulder, Colorado, USA
6Atmospheric and Oceanic Sciences, Princeton University, New Jersey, USA
7Department of Earth System Science, University of California, Irvine, California, USA
8Cooperative Institute for Research in the Environmental Sciences, University of Colorado-Boulder, Boulder, Colorado, USA
9Chemical Sciences Division, NOAA Earth System Research Laboratory, Boulder, Colorado, USA
10Lawrence Livermore National Laboratory, Livermore, California, USA
11Agenzia nazionale per le nuove tecnologie, l'energia e lo sviluppo economico sostenibile (ENEA), Bologna, Italy
12Hadley Centre for Climate Prediction, Met Office, Exeter, UK
13CICERO, Center for International Climate and Environmental Research-Oslo, Oslo, Norway
14School of Geosciences, University of Edinburgh, Edinburgh, UK
15Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
16NASA Goddard Institute for Space Studies, New York City, New York, USA
17GAME/CNRM, Météo-France, CNRS – Centre National de Recherches Météorologiques, Toulouse, France
18National Institute for Environmental Studies, Tsukuba-shi, Ibaraki, Japan
19Royal Netherlands Meteorological Institute, De Bilt, the Netherlands
20Canadian Centre for Climate Modeling and Analysis, Environment Canada, Victoria, British Columbia, Canada
21NASA Goddard Space Flight Center, Greenbelt, Maryland, USA and Universities Space Research Association, Columbia, MD, USA
22Department of Earth and Environmental Science, Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
23Laboratoire des Sciences du Climat et de l'Environnement, LSCE/CEA/CNRS/UVSQ/IPSL, France
24National Institute of Water and Atmospheric Research, Lauder, New Zealand
*now at: Lancaster Environment Centre, Lancaster University, Lancaster, UK
**now at: Department of Meteorology, University of Reading, Reading, UK

Abstract. We have analysed time-slice simulations from 17 global models, participating in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP), to explore changes in present-day (2000) hydroxyl radical (OH) concentration and methane (CH4) lifetime relative to preindustrial times (1850) and to 1980. A comparison of modeled and observation-derived methane and methyl chloroform lifetimes suggests that the present-day global multi-model mean OH concentration is overestimated by 5 to 10% but is within the range of uncertainties. The models consistently simulate higher OH concentrations in the Northern Hemisphere (NH) compared with the Southern Hemisphere (SH) for the present-day (2000; inter-hemispheric ratios of 1.13 to 1.42), in contrast to observation-based approaches which generally indicate higher OH in the SH although uncertainties are large. Evaluation of simulated carbon monoxide (CO) concentrations, the primary sink for OH, against ground-based and satellite observations suggests low biases in the NH that may contribute to the high north–south OH asymmetry in the models. The models vary widely in their regional distribution of present-day OH concentrations (up to 34%). Despite large regional changes, the multi-model global mean (mass-weighted) OH concentration changes little over the past 150 yr, due to concurrent increases in factors that enhance OH (humidity, tropospheric ozone, nitrogen oxide (NOx) emissions, and UV radiation due to decreases in stratospheric ozone), compensated by increases in OH sinks (methane abundance, carbon monoxide and non-methane volatile organic carbon (NMVOC) emissions). The large inter-model diversity in the sign and magnitude of preindustrial to present-day OH changes (ranging from a decrease of 12.7% to an increase of 14.6%) indicate that uncertainty remains in our understanding of the long-term trends in OH and methane lifetime. We show that this diversity is largely explained by the different ratio of the change in global mean tropospheric CO and NOx burdens (ΔCO/ΔNOx, approximately represents changes in OH sinks versus changes in OH sources) in the models, pointing to a need for better constraints on natural precursor emissions and on the chemical mechanisms in the current generation of chemistry-climate models. For the 1980 to 2000 period, we find that climate warming and a slight increase in mean OH (3.5 ± 2.2%) leads to a 4.3 ± 1.9% decrease in the methane lifetime. Analysing sensitivity simulations performed by 10 models, we find that preindustrial to present-day climate change decreased the methane lifetime by about four months, representing a negative feedback on the climate system. Further, we analysed attribution experiments performed by a subset of models relative to 2000 conditions with only one precursor at a time set to 1860 levels. We find that global mean OH increased by 46.4 ± 12.2% in response to preindustrial to present-day anthropogenic NOx emission increases, and decreased by 17.3 ± 2.3%, 7.6 ± 1.5%, and 3.1 ± 3.0% due to methane burden, and anthropogenic CO, and NMVOC emissions increases, respectively.

Citation: Naik, V., Voulgarakis, A., Fiore, A. M., Horowitz, L. W., Lamarque, J.-F., Lin, M., Prather, M. J., Young, P. J., Bergmann, D., Cameron-Smith, P. J., Cionni, I., Collins, W. J., Dalsøren, S. B., Doherty, R., Eyring, V., Faluvegi, G., Folberth, G. A., Josse, B., Lee, Y. H., MacKenzie, I. A., Nagashima, T., van Noije, T. P. C., Plummer, D. A., Righi, M., Rumbold, S. T., Skeie, R., Shindell, D. T., Stevenson, D. S., Strode, S., Sudo, K., Szopa, S., and Zeng, G.: Preindustrial to present-day changes in tropospheric hydroxyl radical and methane lifetime from the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP), Atmos. Chem. Phys., 13, 5277-5298, doi:10.5194/acp-13-5277-2013, 2013.
 
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