Ocean Heat Uptake: Drivers, Variability and Impacts

Climate change is expected to impact human societies in multiple ways. Among the most important impacts are sea level rise and changing weather extremes. This project is set to contribute to our understanding of both factors.
In a warming climate large quantities of heat (up to 90% of the energy due to global warming since 1971) are taken up by the ocean. The heat uptake and penetration depth of the warming is spatially dependent. As a consequence, the ocean warms unequally, and heat is redistributed by (changing) currents. It is essential to understand this spatial heat uptake and (re-)distribution because thermal expansion is an important component of sea level rise.
Due to its large heat capacity, the ocean is the key memory component of the climate, and small changes can have substantial atmospheric consequences, both on large-scale patterns and extreme weather events. Ocean heat uptake variability at various timescales has important effects for atmospheric warming (the warming hiatus in the early 2000s has been attributed to such variability). In addition, the ocean is ultimately the key factor in influencing future extreme events.
In this environment we have identified three knowledge gaps that we address with three key objectives: First, we want to understand the relation between the different air-sea fluxes (short- and longwave radition, sensible and latent heat fluxes) and ocean heat uptake. In doing so, we consider both the ocean response to warming-induced fluxes and the feedback the - such perturbed - ocean exerts on future fluxes. Second, given the importance of ocean heat uptake variability in transient climate change, we aim to separate it into its natural and forced components. Third, we investigate the sensitivity of (magnitude and frequency of) atmospheric extreme events to the sea surface state, in particular concerning patterns of sea surface temperatures but also heat flux components.
The project will involve the use of theory and a hierarchy of models, including coupled and ocean-only general circulation models. In order to relate fluxes to ocean heat uptake, ocean-only models will be used (setups exist that can be deployed), with coupled models used where ocean-atmosphere feedbacks are of interest. The key point is that imposed fluxes can be set separately to explore their contributions to total heat uptake. Of particular use is the FAFMIP experiment that allows to systematically explore the impacts of anomalous air-sea fluxes onto the ocean across different models. For the separation of natural from forced variability we will compare simulations in the "natural" (e.g. preindustrial) and the "forced" climate-change configuration. Very large model ensembles will be required to investigate sensitivities of extreme events, as these events are rare by definition and a large number of possible patterns needs to be scanned. For this purpose we will likely rely upon the distributed-computing system provided by the climateprediction.net project where we can also build on existing setups and configurations. We may initially focus on a specific region (such as Southern Africa) but consider methods to assess global changes.
Taken together, this project will advance our understanding of the role of the ocean in climate and climate change. Links of physical understanding between climate change-induced fluxes, ocean heat uptake, circulation change and extreme events will provide insights in the long-term effects of climate change and improve assessments of likely changes in the coming century.