Regional impacts of climate change and atmospheric CO₂ on future ocean carbon uptake: A multimodel linear feedback analysis

The increase in atmospheric CO₂ over this century depends on the evolution of the oceanic air-sea CO₂ uptake, which will be driven by the combined response to rising atmospheric CO₂ itself and climate change. Here, the future oceanic CO₂ uptake is simulated using an ensemble of coupled climate-carbon cycle models. The models are driven by CO₂ emissions from historical data and the Special Report on Emissions Scenarios (SRES) A2 high-emission scenario. A linear feedback analysis successfully separates the regional future (2010-2100) oceanic CO₂ uptake into a CO₂-induced component, due to rising atmospheric CO₂ concentrations, and a climate-induced component, due to global warming. The models capture the observationbased magnitude and distribution of anthropogenic CO₂ uptake. The distributions of the climate-induced component are broadly consistent between the models, with reduced CO₂ uptake in the subpolar Southern Ocean and the equatorial regions, owing to decreased CO₂ solubility; and reduced CO₂ uptake in the midlatitudes, owing to decreased CO₂ solubility and increased vertical stratification. The magnitude of the climate-induced component is sensitive to local warming in the southern extratropics, to large freshwater fluxes in the extratropical North Atlantic Ocean, and to small changes in the CO₂ solubility in the equatorial regions. In key anthropogenic CO₂ uptake regions, the climate-induced component offsets the CO₂-induced component at a constant proportion up until the end of this century. This amounts to approximately 50% in the northern extratropics and 25% in the southern extratropics and equatorial regions. Consequently, the detection of climate change impacts on anthropogenic CO₂ uptake may be difficult without monitoring additional tracers, such as oxygen.