The positive global carbon cycle climate feedback to anticipated human induced climate change is of 1st order importance (IPCC AR4, 2007). The present spread in model predictions of this feedback is of the same order of magnitude as CO2 emission reduction s which are currently under discussion by policy makers. We will use observations of carbon cycle relevant input variables (forcings) and output variables (carbon cycle tracers) to assess the performance of state-of-the-art carbon cycle component models. These are the models of the marine and terrestrial carbon cycle to be used in the emerging Norwegian coupled Earth system modelling scenarios. We will use in particular the seasonal cycle signal and inter-annual variability to calibrate the sensitivity of the component models. In addition, we will provide a strategy for following up the carbon cycle climate feedback through future observing systems.