Eventual saturation of the climate–carbon cycle feedback studied with a conceptual model

A saturation of climate–carbon cycle feedback was found earlier in the simulations with the IAP RAS climate model of intermediate complexity. Here, this eventual saturation is interpreted by using a conceptual linearised coupled model. It is shown that this saturation is due to weak, logarithmic, dependence of the carbon dioxide radiative forcing on its atmospheric concentration. This eventual saturation leads to the non-monotonic behaviour of climate–carbon cycle parameter f   in time. If the time scale of the atmospheric CO2CO2 build up is tptp then, starting from an initial equilibrium, f   approaches maximum in time ≃tp≃tp. Afterwards, climate–carbon cycle parameter decreases and eventually tends to unity. The time scale of the latter decrease is t1=(1−5)tpt1=(1−5)tp. A dependence of tmtm and t1t1 on governing parameters of the conceptual model is studied. It is argued that an eventual saturation of the climate–carbon cycle feedback is expected to occur also in the other integrations of sufficient length with coupled climate–carbon cycle models.