Dynamics of Ocean Heat Uptake

The ocean plays a crucial role in storing heat and carbon, therefore in setting the spatial and temporal patterns of surface temperature in response to anthropogenic forcing. The magnitude and rate of ocean heat uptake are affected by several key ocean processes such as Southern Ocean Ekman and eddy transports, the North Atlantic Deep Water formation and associated meridional overturning circulation, and diapycnal mixing. Using observations and a range of numerical simulations, we will show that most of the ocean heat uptake has been passive in the past 100 years with very little contribution from changes in ocean dynamics. Under RCP scenarios, changes in the ocean circulation can have a major impact on the heat uptake, however the uncertainty in the rate of uptake can be traced back to uncertainty in air-sea coupling. We will present a simple conceptual framework to explain these results, in the context of the transient climate response to forcing.