Ecosystem responses to rising CO 2 concentrations are a major source of uncertainty in climate change projections. Data from ecosystem-scale Free-Air CO 2 Enrichment (FACE) experiments provide a unique opportunity to reduce this uncertainty. The recent FACE Model-Data Synthesis project aimed to use the information gathered in two forest FACE experiments to assess and improve land ecosystem models. A new 'assumption-centred' model intercomparison approach was used, in which participating models were evaluated against experimental data based on the ways in which they represent key ecological processes. By identifying and evaluating the main assumptions causing differences among models, the assumption-centred approach produced a clear roadmap for reducing model uncertainty. Here, we explain this approach and summarize the resulting research agenda. We encourage the application of this approach in other model intercomparison projects to fundamentally improve predictive understanding of the Earth system.
Bibliographical noteFunding Information:
The ORNL and Duke FACE sites and synthesis activities were supported by the US Department of Energy Office of Science, Biological and Environmental Research programme. This work was initiated under the Benchmarking Ecosystem Response Models with Experimental Data from Long-Term CO2Enrichment Experiments Working Group supported by the National Center for Ecological Analysis and Synthesis, a centre financially supported by the National Science Foundation (grant EF-0553768), the University of California, Santa Barbara, and the state of California. M.D.K. was also supported by ARC discovery grant DP1094791. S.Z. was also supported by the European Community’s Seventh Framework Programme FP7 people programme through grants PERG02-GA-2007-224775 and 238366. T.H. was also supported through the LOEWE initiative for scientific and economic excellence of the German federal state of Hesse. This work is a contribution to the AXA Chair Programme in Biosphere and Climate Impacts and the Grand Challenges in Ecosystems and the Environment initiative at Imperial College. A.K.J. was also supported by the NSF (NSF AGS 12-43071), the US Department of Energy (DOE DE-SC0006706) and NASA LCLUC programme (NASA NNX14AD94G).
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