Background/Question/Methods Top predators, by suppressing herbivores, often have positive indirect effects on plant biomass. We demonstrate, using sea otters as a case study because their indirect impacts on plant biomass have been extensively studied, that this predator effect can substantially reduce atmospheric carbon levels. Results/Conclusions In the presence of sea otters, kelp forest habitats sequester 11% more of the 1.53 kg/m^2 of atmospheric carbon above otter home ranges than they do in the absence of sea otters. For terrestrial predators to have a similar impact on atmospheric carbon sequestration, they would need to reduce plant biomass by 1-10% through indirect effects, depending on the ecosystem. Large predators have been extensively depleted or lost throughout much of the globe and in many places are in rapid decline. We show that maintaining predators where they occur and recovering them where they have been depleted would have a pronounced impact on atmospheric CO2 mitigation.