A theory for the ocean-atmosphere partitioning of anthropogenic carbon dioxide on centennial timescales is presented. The partial pressure of atmospheric CO₂ (P _CO2) is related to the external CO₂ input (ΔΣC) at air-sea equilibrium by: P _CO2 = 280 ppm exp(ΔΣC/[I _A + I _O /R]), where I _A , I _O , 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 P _CO2 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 _CO2 stabilization at present-day transient levels.

©2007 by the American Geophysical Union