We assess the response of atmospheric CO2 (pCO2) and ocean chemistry to carbon perturbations, placing modern carbon-cycle sensitivity in the context of the Cenozoic. We use the carbon-cycle model LOSCAR to study the effect of perturbations over the past 67 Ma. Our results indicate that atmospheric CO2 and surface ocean pH were slightly more sensitive to carbon perturbations during the Miocene (∼15 Ma ago) compared to modern conditions and less sensitive during the earlier part of the Cenozoic. We find that the sensitivity to carbon input at the Paleocene-Eocene boundary (∼56 Ma ago) was most likely lower compared to modern conditions. Further, we show that the Cenozoic evolution of steady state pCO2 and seawater Mg/Ca ratios is critical for the system's sensitivity to a carbon release.