||A diverse set of ecosystem process and land surface models have been parameterized with site and weather data from the Duke University and Oak Ridge National Laboratory free-air CO2 enrichment (FACE) experiments. The ability of the models to reproduce the measured processes of the carbon, water, and nitrogen cycles of the experimental forest stands and their responses to elevated atmospheric CO2 concentration is being evaluated. The long-term (century) implications of the model results will be evaluated, including model tests of the effects of increasing temperature, changes in nitrogen cycling, and step changes in CO2 versus a gradual increase. A new analytical framework for data-model intercomparisons has been developed which permits attribution of model differences into different components so as to isolate sources of variations among model projection. The model-data comparison will be extended to additional long-term, DOE-supported CO2 enrichment experiments (Aspen FACE, Nevada FACE, and open-top chamber experiments in scrub oak and salt marsh ecosystems). This activity will test how the models compare under different circumstances, and provide a broader picture of what model behaviors we should expect. These site-specific analyses will also support and provide increased confidence in projections from a dedicated set of global model experiments, which would allow an analysis of the spatial differences in model responses across a much broader range of environments.