Ocean‐atmosphere partitioning of anthropogenic carbon dioxide on centennial timescales

A theory for the ocean‐atmosphere partitioning of anthropogenic carbon dioxide on centennial timescales is presented. The partial pressure of atmospheric CO 2 ( P CO 2 ) is related to the external CO 2 input (ΔΣ C ) at air‐sea equilibrium by: P CO 2 = 280 ppm exp(ΔΣ C /[ I A + I O / R ]), where I A , I O , and R are the pre‐industrial values of the atmospheric CO 2 inventory, the oceanic dissolved inorganic carbon inventory, and the Revelle buffer factor of seawater, respectively. This analytical expression is tested with two‐ and three‐box ocean models, as well as for a version of the Massachusetts Institute of Technology general circulation model (MIT GCM) with a constant circulation field, and found to be valid by at least 10% accuracy for emissions lower than 4500 GtC. This relationship provides the stable level that P CO 2 reaches for a given emission size, until atmospheric carbon is reduced on weathering timescales. On the basis of the MIT GCM, future carbon emissions must be restricted to a total of 700 GtC to achieve P CO 2 stabilization at present‐day transient levels.