Climate variability on decadal timescales

With the first generation ECBilt model (ECBilt1) we have investigated the interannual to decadal climate variability in the North Atlantic area and the Antarctic Circumpolar Wave (ACW), the possible effects of modulations in solar irradiance on the earth climate, the possiblity for the occurrence of rapid transitions in a 40 kY integration of ECBilt for present day orbital parameters and the predictability of climate on decadal time scales. In all of the above mentioned studies we have done experiments to test the robustness of the results by introducing variations in internal and/or external parameters. We have improved ECBilt1 in several aspects. In the atmospheric model the ratiation code was replaced. The new radiation scheme is a linearisation of the Morcrette scheme and includes the possibility of variations in trace gases like CO2. We are presentyl working on improving the boundary layer scheme. The ocean model was replaced by the MOM model of GFDL and by the CLIO model of the University of Louvain la Neuve. Both models are state of the art ocean models. MOM is less expensive than CLIO and will be used for millennial time-scale variability. CLIO will be used for studying the decadal time-scales. CLIO had a dynamic sea-ice model. With ECBilt2 coupled to CLIO we have performed greenhouse gas concentration scenario experiments and we have also studied the decadal variability in the Arctic which is associated with the dynamics of sea-ice. ECBilt2 will be integrated in the IMAGE model of RIVM for climate change scenario studies.