The carbon cycle is central to the Earth system, being inextricably coupled with climate, the water cycle, nutrient cycles and the production of biomass by photosynthesis on land and in the oceans. A proper understanding of the global carbon cycle is critical for understanding the environmental history of our planet and its human inhabitants, and for predicting and guiding their joint future. The challenge to the scientific community (e.g., the Global Carbon Project) is to monitor (quantify), understand (attribute) and predict the evolution of the carbon cycle in the context of the whole Earth system, including its feedbacks with human components. This demands new scientific approaches and syntheses that cross disciplinary and geographic boundaries and place particular emphasis on the carbon cycle as an integral part of the coupled carbon–climate–human system.

In this context, CarbonFlux will contribute to the efforts of the GCP by exploring and quantifying the incremental value of Earth observation products of the biosphere, hydrosphere and atmosphere on the quality of global scale biophysical and biogeochemical models through multiple constraint assimilation studies. Particular emphasize shall be put on a better understanding of the links and feedbacks of the carbon and hydrologic cycles. The Earth observation products to be considered shall be fAPAr or LAI, soil moisture and total column CO2. In particular CarbonFlux shall:

• Adopt two independent biogeochemical models to allow multiple observations from the hydrosphere, biosphere and atmosphere to be assimilated with the aim to improve terrestrial carbon cycle predictions and refine the assessment of related uncertainties in scenario analyses;
• Run data assimilation experiments to quantify the incremental value of Earth observation products of the biosphere, hydrosphere and atmosphere on the quality of global scale biophysical and biogeochemical models;
• Interpret the model analysis in terms of feedbacks between the hydrologic and carbon cycles and the vulnerability of the terrestrial carbon sinks and pools;
• Produce a global spatially explicit carbon balance, including its component fluxes in form of regional statistics and maps.