Impact of changes in diffuse radiation on the global land carbon sink

• Published in: Nature 2009-04, Vol.458 (7241), p.1014-1017
• Main Authors: Mercado, Lina M, Bellouin, Nicolas, Sitch, Stephen, Boucher, Olivier, Huntingford, Chris, Wild, Martin, Cox, Peter M
• Format: Article
• Language: English
• Subjects: Aerosols; Aerosols - analysis; Aerosols - chemistry; Animal and plant ecology; Animal, plant and microbial ecology; Anthropogenic factors; Atmosphere - chemistry; biogeochemical cycles; biogeochemistry; Biological and medical sciences; canopy; Carbon; Carbon - metabolism; Carbon dioxide; Carbon Dioxide - analysis; Carbon sinks; Climate change; Climate change mitigation; Cloud cover; Clouds; Darkness; Diffusion; Ecosystem; Environmental aspects; Fundamental and applied biological sciences. Psychology; Greenhouse Effect; History, 20th Century; History, 21st Century; Humanities and Social Sciences; letter; Meteorology; multidisciplinary; Observational studies; Photosynthesis; Photosynthesis - radiation effects; plants; Plants - metabolism; Plants - radiation effects; Science; Science (multidisciplinary); Sensitivity analysis; Solar radiation; Sulfates - metabolism; Sunlight; Synecology; Terrestrial ecosystems; vegetation; Volcanic Eruptions
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature07949

Plant photosynthesis tends to increase with irradiance. However, recent theoretical and observational studies have demonstrated that photosynthesis is also more efficient under diffuse light conditions. 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' period, 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.