Sensitivity of the LLN climate model to the astronomical and CO2 forcings over the last 200 ky

The Louvain-la-Neuve climate model there referred to as the LLN 2-D model has been used extensively to simulate the Northern Hemisphere ice volume under both the insolation and CO2 forcings. The period analysed here covers the last 200 ky. First, sensitivity analyses to constant CO2 concentration were performed. The model was accordingly forced by insolation changes only, the CO2 concentration being kept constant to respectively 210, 250 and 290 ppmv. Results show that the simulated ice volume variations are comparable to the geological reconstructions only when the CO2 concentration is low (210 ppmv) and that the sensitivity of the simulated Northern Hemisphere ice volume to CO2 is not constant through time. Second, three CO2 reconstructions were used to force the LLN 2-D model in addition to insolation. Results show (1) a better agreement with the SPECMAP oxygen isotope time series, in particular as far as the amplitude of the signal is concerned, and (2) that the simulated Northern Hemisphere ice volume is not very sensitive to the slight differences between these three reconstructions.