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Indirect radiative forcing of climate change through ozone effects on the land-carbon sink


The evolution of the Earth’s climate over the twenty-first century depends on the rate at which anthropogenic carbon dioxide emissions are removed from the atmosphere by the ocean and land carbon cycles1. Coupled climate–carbon cycle models suggest that global warming will act to limit the land-carbon sink2, but these first generation models neglected the impacts of changing atmospheric chemistry. Emissions associated with fossil fuel and biomass burning have acted to approximately double the global mean tropospheric ozone concentration3, and further increases are expected over the twenty-first century4. Tropospheric ozone is known to damage plants, reducing plant primary productivity and crop yields5, yet increasing atmospheric carbon dioxide concentrations are thought to stimulate plant primary productivity6. Increased carbon dioxide and ozone levels can both lead to stomatal closure, which reduces the uptake of either gas, and in turn limits the damaging effect of ozone and the carbon dioxide fertilization of photosynthesis6. Here we estimate the impact of projected changes in ozone levels on the land-carbon sink, using a global land carbon cycle model modified to include the effect of ozone deposition on photosynthesis and to account for interactions between ozone and carbon dioxide through stomatal closure7. For a range of sensitivity parameters based on manipulative field experiments, we find a significant suppression of the global land-carbon sink as increases in ozone concentrations affect plant productivity. In consequence, more carbon dioxide accumulates in the atmosphere. We suggest that the resulting indirect radiative forcing by ozone effects on plants could contribute more to global warming than the direct radiative forcing due to tropospheric ozone increases.

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Figure 1: Temporal changes of modelled ozone concentrations and gross primary productivity.
Figure 2: Temporal changes in land carbon storage and radiative forcing due to ozone.


  1. Cox, P. M., Betts, R. A., Jones, C. D., Spall, S. A. & Totterdell, I. J. Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model. Nature 408, 184–187 (2000)

    ADS  CAS  Article  Google Scholar 

  2. Friedlingstein, P. et al. Climate-carbon cycle feedback analysis: results from the C4MIP model intercomparison. J. Clim. 19, 3337–3353 (2006)

    ADS  Article  Google Scholar 

  3. Gauss, M. et al. Radiative forcing since preindustrial times due to ozone change in the troposphere and the lower stratosphere. Atmos. Chem. Phys. 6, 575–599 (2006)

    ADS  CAS  Article  Google Scholar 

  4. Gauss, M. et al. Radiative forcing in the 21st century due to ozone changes in the troposphere and the lower stratosphere. J. Geophys. Res. 108 4292 doi: 10.1029/2002JD002624 (2003)

    Google Scholar 

  5. Ashmore, M. R. Assessing the future global impacts of ozone on vegetation. Plant Cell Environ. 28, 949–964 (2005)

    CAS  Article  Google Scholar 

  6. Karnosky, D. F. et al. Tropospheric O3 modulates responses of temperate hardwood forests to elevated CO2: a synthesis of molecular to ecosystem results from the Aspen FACE project. Funct. Ecol. 17, 289–304 (2003)

    Article  Google Scholar 

  7. Gedney, N. et al. Detection of a direct carbon dioxide effect in continental river runoff records. Nature 439, 835–838 (2006)

    ADS  CAS  Article  Google Scholar 

  8. Forster, P. et al. in Climate Change 2007: The Physical Science Basis (eds Solomon, S. et al.) 129–234 (Cambridge Univ. Press, Cambridge, UK, 2007)

  9. Wang, X. & Mauzerall, D. L. Characterizing distributions of surface ozone and its impact on grain production in China, Japan and South Korea: 1900 and 2020. Atmos. Environ. 38, 4383–4402 (2004)

    ADS  CAS  Article  Google Scholar 

  10. Prather, M. et al. in Climate Change 2001: The Scientific Basis (eds Houghton, J. T. et al.) 239–287 (Cambridge Univ. Press, Cambridge, UK, 2001)

    Google Scholar 

  11. Felzer, B. S. et al. Future effects of ozone on carbon sequestration and climate change policy using a global biogeochemical model. Clim. Change 73 345–373 doi: 10.1007/s10584-005-6776-4 (2005)

    ADS  CAS  Article  Google Scholar 

  12. Field, C., Jackson, R. & Mooney, H. Stomatal responses to increased CO2: implications from the plant to the global-scale. Plant Cell Environ. 18, 1214–1255 (1995)

    Article  Google Scholar 

  13. Karnosky, D. F. et al. Scaling ozone responses of forest trees to the ecosystem level in a changing climate. Plant Cell Environ. 28, 965–981 (2005)

    CAS  Article  Google Scholar 

  14. Volk M. et al. Grassland yield declined by a quarter in 5 years of free-air ozone fumigation. Glob. Change Biol. 12 74–83 doi: 10.1111/j.1365-2486.2005.01083.x (2006)

    ADS  Article  Google Scholar 

  15. Percy, K. E. et al. New exposure-based metric approach for evaluating O3 risk to North American aspen forests. Environ. Pollut. 147, 554–566 (2007)

    CAS  Article  Google Scholar 

  16. Pleijel, H. et al. Relationships between ozone exposure and yield loss in European wheat and potato — a comparison of concentration- and flux-based exposure indices. Atmos. Environ. 38, 2259–2269 (2004)

    ADS  CAS  Article  Google Scholar 

  17. Essery, R. L. H., Best, M. J., Betts, R. A., Cox, P. M. & Taylor, C. M. Explicit representation of sub-grid heterogeneity in a GCM land-surface scheme. J. Hydrometeorol. 4, 530–543 (2001)

    ADS  Article  Google Scholar 

  18. Cox, P. M. et al. The impact of new GCM land-surface physics on the GCM simulation of climate and climate sensitivity. Clim. Dyn. 15, 183–203 (1999)

    Article  Google Scholar 

  19. Sanderson, M. G., Jones, C. D., Collins, W. J., Johnson, C. E. & Derwent, R. G. Effect of climate change on isoprene emissions and surface ozone levels. Geophys. Res. Lett. 30 1936 doi: 10.1029/2003GL017642 (2003)

    ADS  Google Scholar 

  20. Karlsson, P. E. et al. New critical levels for ozone effects on young trees based on AOT40 and simulated cumulative leaf uptake of ozone. Atmos. Environ. 38, 2283–2294 (2004)

    ADS  CAS  Article  Google Scholar 

  21. New, M., Hulme, M. & Jones, P. Representing twentieth-century space-time climate variability. Part II. Development of 1901–96 monthly grids of terrestrial surface climate. J. Clim. 13, 2217–2238 (2000)

    ADS  Article  Google Scholar 

  22. Denman, K. L. et al. in Climate Change 2007: The Physical Science Basis (eds Solomon, S. et al.) 499–587 (Cambridge Univ. Press, Cambridge, UK, 2007)

    Google Scholar 

  23. Imhoff, M. L. et al. Global patterns in human consumption of net primary production. Nature 429, 870–873 (2004)

    ADS  CAS  Article  Google Scholar 

  24. Schröter, D. et al. Ecosystem service supply and vulnerability to global change in Europe. Science 310 1333–1337 doi: 10.1126/science.1115233 (2005)

    ADS  Article  Google Scholar 

  25. Nussbaum, S. & Fuhrer, J. Difference in ozone uptake in grassland species between open-top chambers and ambient air. Environ. Pollut. 109, 463–471 (2000)

    CAS  Article  Google Scholar 

  26. Sabine, C. L. et al. The oceanic sink for anthropogenic CO2 . Science 305, 367–371 (2004)

    ADS  CAS  Article  Google Scholar 

  27. Berntsen, T. K., Myhre, G., Stordal, F. & Isaksen, I. S. A. Time evolution of tropospheric ozone and its radiative forcing. J. Geophys. Res. 105, 8915–8930 (2000)

    ADS  CAS  Article  Google Scholar 

  28. Ramaswamy, V. et al. in Climate Change 2001: The Scientific Basis (eds Houghton, J. T. et al.) 350–416 (Cambridge Univ. Press, Cambridge, UK, 2001)

  29. Dentener, F. D. et al. The global atmospheric environment for the next generation. Environ. Sci. Technol. 40, 3586–3594 (2005)

    ADS  Article  Google Scholar 

  30. van der Werf, G. R., Randerson, J. T., Collatz, G. J. & Giglio, L. Carbon emissions from fires in tropical and subtropical ecosystems. Glob. Change Biol. 9, 547–562 (2003)

    ADS  Article  Google Scholar 

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We thank N. Gedney for technical support, and M. Sanderson for information on the STOCHEM fields used in this study; we acknowledge discussions with the aforementioned and with M. Ashmore, R. Betts, D. Hemming, O. Boucher and L. Mercado. We also thank A. Everitt for computer support. S.S. was supported by the UK Department for Environment, Food and Rural Affairs (DEFRA) Climate Prediction Programme. W.J.C. was supported by the MoD, and by DEFRA Air and Environment Quality Division, and C.H. by the UK Natural Environment Research Council.

Author Contributions P.M.C. developed the modification to MOSES to include ozone effects on photosynthesis and stomatal conductance; W.J.C. provided the projections of future changes in tropospheric ozone; C.H. developed the IMOGEN software that enabled the global simulations to be carried out; and S.S. calibrated the ozone effects model against data from manipulative field experiments, and carried out and analysed the global simulations. All four authors were involved in the drafting of the paper, although SS took the lead role.

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Correspondence to S. Sitch.

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Sitch, S., Cox, P., Collins, W. et al. Indirect radiative forcing of climate change through ozone effects on the land-carbon sink. Nature 448, 791–794 (2007).

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