Reemergence of Anthropogenic Carbon Into the Ocean’s Mixed Layer Strongly Amplifies Transient Climate Sensitivity

Rodgers, K. B., Schlunegger, S., Slater, R. D., Ishii, M., Frölicher, T. L., Toyama, K., Plancherel, Y., Aumont, O., & Fassbender, A. J. (2020). Reemergence of Anthropogenic Carbon Into the Ocean’s Mixed Layer Strongly Amplifies Transient Climate Sensitivity. Geophysical Research Letters, 47 (18), e2020GL089275. https://doi.org/10.1029/2020GL089275

Summary:

In this work, the authors demonstrate that the net ocean uptake of anthropogenic carbon is strongly sensitive to perturbations in the CO₂ buffering capacity of surface ocean waters. This result is closely connected to the process of reemergence of anthropogenic carbon from the ocean interior to the surface mixed layer. In this paper, they used an ocean circulation‐carbon cycle model to identify an upper limit on the impact of reemergence of anthropogenic carbon into the ocean’s mixed layer on the cumulative airborne fraction of CO₂ in the atmosphere. They find under an RCP8.5 emissions pathway (with steady circulation) that the cumulative airborne fraction of CO₂ has a sevenfold reduction by 2100 when the CO₂ buffering capacity of surface seawater is maintained at preindustrial levels. The results indicate that the effect of reemergence of anthropogenic carbon into the mixed layer on the buffering capacity of CO₂ amplifies the transient climate sensitivity of the Earth system.