The real carbon cycle has multiple reservoirs and adjustment times, rather than one universally exponential removal process. Air-sea exchange, ocean mixing and carbonatechemistry give a long-lived atmospheric tail; uptake also changes with temperature, circulation and carbon loading. For example, a warming ocean can absorb less additional carbon dioxide, so a fixed b0 omits a potentially positive climate-carbonfeedback. Terrestrial vegetation and soil responses provide further examples. One missing feature is the dependence of carbon uptake on the changing state of the ocean and climate.
