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

A positive marine chemistry‐climate feedback was originally proposed by Revelle and Suess (1957, https://doi.org/10.3402/tellusa.v9i1.9075), whereby the invasion flux of anthropogenic carbon into the ocean serves to inhibit future marine CO2 uptake through reductions to the buffering capacity of surface seawater. Here we use 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. We 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. Our 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. Key Points: Marine chemistry‐climate feedbacks plan an important role in determining climate sensitivityThe rate of reemergence of anthropogenic carbon plays an important role in determining climate sensitivityThe sensitivity identified here to perturbations to the buffering capacity of CO2 in seawater is larger than that emphasized in IPCC AR5 [ABSTRACT FROM AUTHOR]