Regional Impacts of Climate Change and Atmospheric CO

The increase in atmospheric CO sub(2) over this century depends on the evolution of the oceanic air-sea CO sub(2) uptake, which will be driven by the combined response to rising atmospheric CO sub(2) itself and climate change. Here, the future oceanic CO sub(2) uptake is simulated using an ensemble of coupled climate-carbon cycle models. The models are driven by CO sub(2) 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 CO sub(2) uptake into a CO sub(2)-induced component, due to rising atmospheric CO sub(2) concentrations, and a climate-induced component, due to global warming. The models capture the observation-based magnitude and distribution of anthropogenic CO sub(2) uptake. The distributions of the climate-induced component are broadly consistent between the models, with reduced CO sub(2) uptake in the subpolar Southern Ocean and the equatorial regions, owing to decreased CO sub(2) solubility; and reduced CO sub(2) uptake in the midlatitudes, owing to decreased CO sub(2) 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 CO sub(2) solubility in the equatorial regions. In key anthropogenic CO sub(2) uptake regions, the climate-induced component offsets the CO sub(2)-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 CO sub(2) uptake may be difficult without monitoring additional tracers, such as oxygen.