The Kyoto protocol and the agreement reached at Bonn requires an assessment of the net carbon balance at different scales, ranging from projects and nations to continents. In the following we give an overview about the biological control of net carbon fluxes. Depending on the processes under consideration, these range from gross primary productivity, GPP (photosynthesis), and net primary productivity, NPP (plant growth), to net ecosystem productivity, NEP (CO₂ assimilation minus heterotrophic respiration), and net biome productivity, NBP, including non-respiratory losses, such as by harvest and fire. We give an overview about the quantification of these processes based on Europe and Siberia. The Kyoto commitment is focused on the woody component of NPP, which is in the order of 1 to 2 t C ha^-1 year^-1. But, if all respiratory and non-respiratory losses are considered, the NBP decreases to less than 0.5 t C ha^-1 year^-1. Given the uncertainty of the assessments, and the difference between NPP and NBP it appears questionable to include biological sinks into the carbon accounting of fossil fuel emissions.