Plant photosynthesis tends to increase with irradiance. However, recent theoretical and observational studies have demonstrated that photosynthesis is also more efficient under diffuse light conditions1,2,3,4,5. Changes in cloud cover or atmospheric aerosol loadings, arising from either volcanic or anthropogenic emissions, alter both the total photosynthetically active radiation reaching the surface and the fraction of this radiation that is diffuse, with uncertain overall effects on global plant productivity and the land carbon sink. Here we estimate the impact of variations in diffuse fraction on the land carbon sink using a global model modified to account for the effects of variations in both direct and diffuse radiation on canopy photosynthesis. We estimate that variations in diffuse fraction, associated largely with the ‘global dimming’ period6,7,8, enhanced the land carbon sink by approximately one-quarter between 1960 and 1999. However, under a climate mitigation scenario for the twenty-first century in which sulphate aerosols decline before atmospheric CO2 is stabilized, this ‘diffuse-radiation’ fertilization effect declines rapidly to near zero by the end of the twenty-first century.
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Goudriaan, J. Crop Micrometeorology: A Simulation Study 5–72 (Centre for Agricultural Publishing and Documentation, 1977)
Gu, L. H. et al. Response of a deciduous forest to the Mount Pinatubo eruption: enhanced photosynthesis. Science 299, 2035–2038 (2003)
Roderick, M. L., Farquhar, G. D., Berry, S. L. & Noble, I. R. On the direct effect of clouds and atmospheric particles on the productivity and structure of vegetation. Oecologia 129, 21–30 (2001)
Niyogi, D. et al. Direct observations of the effects of aerosol loading on net ecosystem CO2 exchanges over different landscapes. Geophys. Res. Lett. 31 10.1029/2004Gl020915 (2004)
Oliveira, P. H. F. et al. The effects of biomass burning aerosols and clouds on the CO2 flux in Amazonia. Tellus B 59, 338–349 (2007)
Stanhill, G. & Cohen, S. Global dimming: a review of the evidence for a widespread and significant reduction in global radiation with discussion of its probable causes and possible agricultural consequences. Agric. For. Meteorol. 107, 255–278 (2001)
Liepert, B. G. Observed reductions of surface solar radiation at sites in the United States and worldwide from 1961 to 1990. Geophys. Res. Lett. 29 10.1029/2002Gl014910 (2002)
Wild, M. et al. From dimming to brightening: decadal changes in solar radiation at Earth’s surface. Science 308, 847–850 (2005)
Jones, C. D., Cox, P. M., Essery, R. L. H., Roberts, D. L. & Woodage, M. J. Strong carbon cycle feedbacks in a climate model with interactive CO2 and sulphate aerosols. Geophys. Res. Lett. 30 10.1029/2003Gl016867 (2003)
Mercado, L. M., Huntingford, C., Gash, J. H. C., Cox, P. M. & Jogireddy, V. Improving the representation of radiation interception and photosynthesis for climate model applications. Tellus B 59, 553–565 (2007)
Dai, Y. J., Dickinson, R. E. & Wang, Y. P. A two-big-leaf model for canopy temperature, photosynthesis, and stomatal conductance. J. Clim. 17, 2281–2299 (2004)
Knohl, A., Schulze, E. D., Kolle, O. & Buchmann, N. Large carbon uptake by an unmanaged 250-year-old deciduous forest in central Germany. Agric. For. Meteorol. 118, 151–167 (2003)
Rebmann, C. et al. Influence of transport processes on CO2-exchange at a complex forest site in Thuringia, Germany. Agric. For. Meteorol. (submitted)
Knohl, A. & Baldocchi, D. D. Effects of diffuse radiation on canopy gas exchange processes in a forest ecosystem. J. Geophys. Res. 113 10.1029/2007JG000663 (2008)
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)
Bellouin, N. Improved Representation of Aerosols for HadGEM2. Technical Note 73, 〈http://www.metoffice.gov.uk/publications/HCTN/HCTN_73.pdf〉 (Met Office Hadley Centre, 2007)
Sato, M., Hansen, J., McCormick, M. & Pollack, J. Stratospheric aerosol optical depths, 1850–1990. J. Geophys. Res. 98, 22987–22994 (1993)
van Vuuren, D. P. et al. Stabilizing greenhouse gas concentrations at low levels: an assessment of reduction strategies and costs. Clim. Change 81, 119–159 (2007)
Forster, P. et al. in Climate Change 2007: The Physical Science Basis (eds Solomon, S. et al.) 129–234 (Cambridge Univ. Press, 2007)
Gu, L., Fuentes, J. D., Shugart, H. H., Staebler, R. M. & Black, T. A. Responses of net ecosystem exchanges of carbon dioxide to changes in cloudiness: results from two North American deciduous forests. J. Geophys. Res. 104, 31421–31434 (1999)
Ciais, P., Tans, P. P., Trolier, M., White, J. W. C. & Francey, R. J. A large northern-hemisphere terrestrial CO2 sink indicated by the C-13/C-12 ratio of atmospheric CO2 . Science 269, 1098–1102 (1995)
Keeling, C. D., Whorf, T. P., Wahlen, M. & Vanderplicht, J. Interannual extremes in the rate of rise of atmospheric carbon-dioxide since 1980. Nature 375, 666–670 (1995)
Lucht, W. et al. Climatic control of the high-latitude vegetation greening trend and Pinatubo effect. Science 296, 1687–1689 (2002)
Jones, C. D. & Cox, P. M. Modeling the volcanic signal in the atmospheric CO2 record. Glob. Biogeochem. Cycles 15, 453–465 (2001)
Buitenhuis, E. et al. Biogeochemical fluxes through mesozooplankton. Glob. Biogeochem. Cycles 20 10.1029/2005GB002511 (2006)
Romanou, A. et al. 20th century changes in surface solar irradiance in simulations and observations. Geophys. Res. Lett. 34 10.1029/2006GL028356 (2007)
Liepert, B. & Tegen, I. Multidecadal solar radiation trends in the United States and Germany and direct tropospheric aerosol forcing. J. Geophys. Res. 107 10.1029/2001JD000760 (2002)
Power, H. C. Trends in solar radiation over Germany and an assessment of the role of aerosols and sunshine duration. Theor. Appl. Climatol. 75, 47–63 (2003)
Russak, V. Changes in solar radiation and their influence on temperature trend in Estonia (1955–2007). J. Geophys. Res. 114 10.1029/2008JD010613 (2009)
Long, C. N., Dutton, E. G., Augustine, J. A., Wiscombe, W. & Wild, M. Investigations of surface downwelling solar radiation for the continental US. J. Geophys. Res. (in the press)
Key, J. R. & Schweiger, A. J. Tools for atmospheric radiative transfer: Streamer and FluxNet. Comput. Geosci. 24, 443–451 (1998)
We thank A. Knohl and C. Rebmann for supplying the eddy flux data for model evaluation, D. van Vuuren and the group that developed the IMAGE model for providing scenario data for the simulation of the twenty-first century. We also thank C. D. Jones for advice on the experimental design, C. M. Taylor for discussions on early results, R. Ellis and P. Harris for both scientific and technical support, A. Everitt for computer support and G. Weedon for discussions. The authors acknowledge funding from the UK Natural Environment Research Council CLASSIC programme (L.M.M., C.H. and P.M.C.) and the UK Department for Environment, Food and Rural Affairs (Defra) and the UK Ministry of Defence (MoD) (N.B., O.B. and S.S.) under GA01101 (Defra) and CBC/2B/0417_Annex C5 (MoD) and from the Swiss NCCR Climate (M.W.).
Author Contributions L.M.M. and P.M.C. developed the modification of the JULES model to include sunfleck penetration through the canopy. L.M.M. validated the model at site level, analysed and performed the global simulations and wrote the initial version of the manuscript. O.B. and N.B. developed the framework for producing the shortwave and PAR fields. N.B. developed the look-up tables to reconstruct shortwave and PAR fields under clear- and cloudy-sky conditions and validated the output against ground-based observations. O.B. provided the sulphate aerosol burden for the simulation of the twenty-first century. P.M.C. contributed to the entire study and S.S. contributed to the analysis of results. C.H. developed the IMOGEN software that enabled the global simulations to be carried out. M.W. provided ground-based observations of shortwave- and diffuse-radiation time series and also advised on model validation. All authors discussed the results and the structure of the paper and developed and improved the manuscript.
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Mercado, L., Bellouin, N., Sitch, S. et al. Impact of changes in diffuse radiation on the global land carbon sink. Nature 458, 1014–1017 (2009). https://doi.org/10.1038/nature07949
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