Impact of Ocean Dynamics on Polar Climate Change

The role of ocean dynamics in high-latitude climate change remains uncertain: while model intercomparison studies suggest that amplification of high-latitude warming is strongly correlated with ocean heat transports into the polar regions (see, e.g., Holland & Bitz 2003; Hwang et al 2011), radiative feedback studies indicate only a minor role for the ocean (Pithan & Mauritsen 2014). In this study, we attempt to resolve this conflicting evidence by directly inspecting how changes in ocean dynamics with quasi-equilibrium CO₂-doubling impact high-latitude climate. With CO₂-doubling, we find a poleward shift in the ocean heat flux convergence (OHFC) in winter in both hemispheres. By prescribing this pattern of anomalous OHFC in a series of global climate model experiments utilizing a slab ocean model (SOM; see Table 1), we isolate the impact of these changes in ocean dynamics associated with CO₂-doubling on the polar climate system. We show that this pattern of perturbed OHFC is associated with a poleward shift in ocean-to-atmosphere turbulent heat fluxes (both sensible and latent) and sea ice retreat in both the Arctic and Antarctic (Figure 1, contours). The high-latitudes warm while the midlatitudes cool (Figure 1, colors), thereby amplifying polar warming at the expense of extrapolar warming and enhancing high-latitude climate sensitivity. Furthermore, midlatitude cooling is propagated to the polar mid-troposphere on moist isentropic surfaces; as a result, the (positive) lapse rate feedback is augmented at high latitudes. Our results highlight a fundamental asymmetry in how changes in oceanic and atmospheric energy transports impact polar climate, and provide further evidence that the partitioning of meridional energy transport changes between the atmosphere and ocean is a key factor in high-latitude climate change.