Ocean‐atmosphere partitioning of anthropogenic carbon dioxide on centennial timescales

Abstract

A theory for the ocean‐atmosphere partitioning of anthropogenic carbon dioxide on centennial timescales is presented. The partial pressure of atmospheric CO2 (PCO2) is related to the external CO2 input (ΔΣC) at air‐sea equilibrium by: PCO2 = 280 ppm exp(ΔΣC/[IA + IO/R]), where IA, IO, and R are the pre‐industrial values of the atmospheric CO2 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 PCO2 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 PCO2 stabilization at present‐day transient levels.