How Asymmetries Between Arctic and Antarctic Climate Sensitivity are Modified by the Ocean

We investigate the impact of the evolving ocean response to CO₂-forcing on hemispheric asymmetries in polar climate sensitivity. Intermodel comparison of CMIP5 CO₂-quadrupling experiments shows that even in models where hemispheric ocean heat uptake (OHU) differences are small, warming over the Arctic still substantially exceeds that over the Antarctic. The polar climate impact of this evolving ocean response to CO₂ forcing is then isolated using slab ocean experiments in the state-of-the-art Community Earth System Model. For all time scales and regions, climate feedbacks over the southern hemisphere more effectively dissipate top-of-atmosphere anomalies than those over the northern hemisphere. Furthermore, a poleward shift in ocean heat convergence in both hemispheres amplifies destabilizing ice-albedo and lapse rate feedbacks in the Arctic much more than in the Antarctic. These results suggest that the Arctic is intrinsically more sensitive to both CO₂ and oceanic forcings than the Antarctic, and that ocean-driven climate sensitivity asymmetry can be attributed to amplification of feedbacks over the Arctic rather than the stabilization of feedbacks over the Antarctic. Therefore, neither hemispheric asymmetries in ocean heat uptake nor ocean heat transport need to be invoked to explain baseline asymmetries between Arctic and Antarctic climate responses.