Which processes most strongly govern terrestrial carbon cycle feedbacks in Earth system models?

Graphic comparing various turnover times for carbon in vegetation and soil carbon pools.

ESMs (Earth system models) are crucial in estimating climate sensitivity, but show large uncertainty in carbon cycle feedbacks. A key step of reducing this uncertainty is to identify the processes that govern carbon-climate and carbon-concentration feedbacks driven by changes in terrestrial carbon stocks. Are these changing carbon stocks driven by changes to inputs, or changes to output in C pools? And do these changes mostly occur in live vegetation, or in dead soil carbon pools?

Charles Koven, with team members Jeff Chambers, Katerina Georgiou, Ryan Knox, Robinson Negron-Juarez, Bill Riley (all EESA-LBNL researchers), and Vivek Arora (Canadian Centre for Climate Modelling and Analysis), Victor Brovkin (Max Planck Institute for Meteorology, Germany), Pierre Friedlingstein (University of Exeter), and Chris Jones, Met Office Hadley Centre Climate Science and Service, Exeter, developed a theoretical framework for separating these controls, and applied it to the CMIP5 models. They found that for the CMIP5 ESMs, initial condition uncertainty is driven by uncertainty in turnover times, whereas transient uncertainty is driven by changes to productivity. These patterns hold for both live and dead ecosystem components. This points to the need to determine in greater detail the processes that control turnover times of both vegetation and soil carbon pools, and to discern whether these processes are adequately represented in the models.

Primary support: Office of Science, Office of Biological and Environmental Research of the U.S. Department of Energy, as part of their Regional and Global Climate Modeling Program.

Citation: C. D. Koven, J. Q. Chambers, K. Georgiou, R. Knox, R. I. Negron-Juarez, W. J. Riley, V. Arora, V. Brovkin, P. Friedlingstein, and C. D. Jones. Controls on terrestrial carbon feedbacks by productivity versus turnover in the CMIP5 Earth System Models. Biogeosciences 12: 5211-5228, 2015. doi:10.5194/bg-12-5211-2015. Published September 7, 2015.

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