The focus of DOE carbon cycle research is primarily on Terrestrial Carbon Processes (TCP) and provides scientific knowledge of terrestrial components of the global carbon cycle. In general, the TCP research provides insight into the fate of excess CO2 from human activities, including a scientific understanding of carbon cycle mechanisms and controls on CO2 as a forcing factor of climate change. Objectives are to (i) provide accurate predictions of atmospheric CO2 change; (ii) quantify terrestrial carbon sources and sinks and how they are changing in relation to other atmospheric, climatologic and hydrologic influences; (iii) assess terrestrial feedbacks on carbon cycle and climate; and (iv) use modeling approaches. TCP results from these investigations are extended to larger scales, thereby contributing to continental scale analysis of carbon sources and sinks.

Four components of the TCP Program include AmeriFlux, the FACE experiments, soil carbon research and carbon cycle modeling. 

• AmeriFlux focuses primarily on net ecosystem exchange of CO2 using the eddy covariance method (although data on water and energy flux are also obtained), with supporting observations of ecological/biological/physiological processes at the ecosystem scale.
• FACE experiments focus on the processes by which elevated CO2 (eCO2) influences carbon cycle dynamics, and includes measures of ecosystem level responses to eCO2.
• Soil carbon research involves quantification of rates and magnitudes of soil carbon accretion, including processes and properties that control transformation of biomass into soil organic matter and stabilization mechanisms of the long residence time components.
• Terrestrial carbon cycle modeling focuses on the assimilation of ecosystem-scale carbon cycle processes, and taking advantage of AmeriFlux, FACE, NACP and other data products, to develop an architecture for integrating and evaluating the terrestrial carbon cycle at regional and continental scales. 

In addition, TCP supports carbon isotope tracer research as a powerful method for understanding and quantifying carbon transformations, and for estimating rate parameters of terrestrial carbon processes. The research involves state-of-the-art observations and experiments that provide a quantitative and predictive understanding of the terrestrial carbon cycle processes that can affect atmospheric CO2 trends and inter-annual variability, which influence the CO2 forcing of climate. TCP research contributes observations, experimental results and models to regional or continental scale analysis of CO2 exchange, including new knowledge of terrestrial carbon sources and sinks needed for periodic assessments of the State of the Carbon Cycle for North America.