Global Pattern Formation of Net Ocean Surface Heat Flux Response to Greenhouse Warming

This study examines global patterns of net ocean surface heat flux changes (Delta Q(net)) under greenhouse warming in an ocean-atmosphere coupled model based on a heat budget decomposition. The regional structure of Delta Q(net) is primarily shaped by ocean heat divergence changes (Delta OHD): excessive heat is absorbed by higher-latitude oceans (mainly over the North Atlantic and the Southern Ocean), transported equator-ward, and stored in lower-latitude oceans with the rest being released to the tropical atmosphere. The overall global pattern of Delta OHD is primarily due to the circulation change and partially compensated by the passive advection effect, except for the Southern Ocean, which requires further investigations for a more definitive attribution. The mechanisms of North Atlantic surface heat uptake are further explored. In another set of global warming simulations, a perturbation of freshwater removal is imposed over the subpolar North Atlantic to largely offset the CO2-induced changes in the local ocean vertical stratification, barotropic gyre, and the Atlantic meridional overturning circulation (AMOC). Results from the freshwater perturbation experiments suggest that a significant portion of the positive Delta Q(net) over the North Atlantic under greenhouse warming is caused by the Atlantic circulation changes, perhaps mainly by the slowdown of AMOC, while the passive advection effect can contribute to the regional variations of Delta Q(net). Our results imply that ocean circulation changes are critical for shaping global warming pattern and thus hydrological cycle changes.