Changes in the Global Carbon Cycle and Ocean Circulation on the Millennial Time Scale

Carbon dioxide is, after water vapor, the most important greenhouse gas. Naturally, its atmospheric concentration has varied between 190 and 290 ppmv over the last half million years. The man-made CO2 increase of the last 250 years has already reached this amplitude with the potential of inducing signi¯cant global warming. Climate models suggest that the ocean circulation reacts in a sensitive way to global warming in that large circulation systems can break down. Here we discuss the question of potential feedback mechanisms between the global carbon cycle and the ocean circulation. This is done by ¯rst examining the paleoclimatic record of past CO2 changes obtained from polar ice cores. Modelling experiments provide a quantitative interpretation of the changes found in these records.