Figure S1. Conceptual diagram of observations available for testing carbon-climate models. Ice core measurements of the atmospheric CO2 record provide constraints on the sum of ocean and land carbon fluxes when this information is combined with fossil fuel inventory time series. Isotope measurements from ice cores allow for similar constraints but including gross exchanges and reservoir turnover times. Contemporary atmospheric CO2 observations from flask networks (NOAA GMD) and satellites (e.g., the Orbiting Carbon Observatory) provide information about the seasonal dynamics of net ecosystem exchange and continental-scale fluxes on timescales of years to decades. Biomass inventories are sparse but crucial for constraining allocation, tree mortality, and the mass of carbon vulnerable to deforestation. Satellite observations of leaf area index and other ecosystem variables provide global coverage at a high temporal resolution for a period of almost three decades, although cross-platform calibrations introduce considerable uncertainty. Free-Air Carbon dioxide Enrichment (FACE) experiments have quantified elevated CO2 effects on ecosystem processes in temperate ecosystems, but less information exists for tropical forest and boreal biomes that account for most of terrestrial GPP and aboveground carbon storage.

Figure S2. Comparison of net primary production for a) CASA' and b) CN models with class A observations from the Ecosystem Model Data Intercomparison Initiative (EMDI). The same comparison for class B observations is shown in c) and d).

Figure S3. Zonal mean net primary production from MODIS satellite-based estimates compared with the models. We used the MOD17A3 collection 4.5 product from MODIS for this comparison (Heinsch et al., 2003). We show the 200-2004 zonal mean and compare this model experiment 1.4 during the same period.

Figure S4. The zonal mean response of NPP to a step change in atmospheric CO2 following the FACE experimental protocol. The model NPP response was averaged over the first 5 years after enrichment.

Figure S5. a) The global net land flux from experiment 1.4. This simulation includes climate variability and time-varying atmospheric CO2 and nitrogen deposition. Climate for a 25-year span (1948-1972) was cycled until 1948, the beginning of the NCAR/NCEP reanalysis period. b) The difference in flux between experiments 1.4 and the climate only simulation (experiment 1.3). This panel shows the fluxes caused solely from the atmospheric CO2 and nitrogen deposition forcing. c) The land flux driven solely by climate (experiment 1.3) during 1973-2004.

Figure S6. Conceptual diagram showing how a climate ecosystem data-model intercomparison system (CEDMIS) might function in the context of existing data centers and model archiving capabilities. CEDMIS would extract information from archived data sets and models to generate intercomparison diagnostics, using a series of scoring, visualization, and data extraction software tools. A key goal would be make the intercomparison diagnostics into modules that could be reused in multiple model-intercomparison projects (MIPs) in an open source format. This system could be used in a stand alone mode for individual model development or as the basis for community wide MIPs. Key data sources would include the Carbon Dioxide Information and Analysis Center (CDIAC), NASA's Oak Ridge National Lab (ORNL) and Land Processes (LP) Distributed Active Archiving Centers (DAACs), NOAA's Global Monitoring Division trace gas archives (including retrieved fluxes by means of atmospheric inversions such as TRANSCOM and CarbonTracker), and NSF's Long Term Ecological Research (LTER).

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