Persistence of North Atlantic ocean heat uptake following CO2 concentration maximum

Most of net energy captured by the increase in greenhouse gasses are subsequently absorbed by the oceans, with the majority being taken up by the subpolar North Atlantic and the Southern Ocean, in the form of ocean heat uptake (OHU). In this study, we examine the temporal evolution of OHU from the Coupled Model Intercomparison Project Phase 5&6 (CMIP 5&6) data, with a focus on the time period that would follow reaching CO2 concentration maximum. Our results show that the Southern Ocean and global mean OHU would show a negative trend following abrupt CO2 quadrupling. In contrast, the OHU in the subpolar North Atlantic would still rise and then remain at a high level for a century or longer. The SSP experiments show the same phenomenon when CO2 concentration starts decreasing. This opposite trend of OHU between the Southern Ocean and subpolar North Atlantic is mainly driven by the surface latent heat flux. Further analysis and a freshwater perturbation experiment using a coupled ocean-atmosphere model suggest that the prolonged period of strong OHU over the North Atlantic in the post-CO2 concentration maximum era would be the result of an overshoot of the Atlantic Meridional Overturning Circulation (AMOC) in response to the increase of CO2 concentration.