10.15.2016

CO2 and greening observations indicate increasing light-use efficiency in northern terrestrial ecosystems

2 (ASC) north of 45° N of 56 ± 9.8% over the last 50 years and an increase in vegetation greenness of 7.5-15% in high northern latitudes since the 1980’s. However the causes of these changes remain uncertain. Historical simulations from terrestrial biosphere models in the Multi-scale Synthesis and Terrestrial Model Inter-comparison Project (MsTMIP) are compared to the ASC and greenness observations, using the TM3 atmospheric transport model to translate surface fluxes into CO2 concentrations. We find that the modelled change in ASC is too small but the mean greening trend is generally captured. Modelled increases in greenness are primarily driven by warming whereas ASC changes are primarily driven by increasing CO2. We suggest that increases in ecosystem-scale light-use efficiency (LUE) have contributed to the observed ASC increase, but are underestimated by current models. We highlight potential mechanisms that could increase modelled LUE. The complete article, which appeared in Geophysical Research Letters (Vol. 43, Issue 18, Sept. 28, 2016) of the American Geophysical Union, is available at http://onlinelibrary.wiley.com/doi/10.1002/2016GL070710/abstract]]>

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