The Arctic warming response to increasing greenhouse gas is substantially greater than the rest of the globe. It has been suggested that this phenomenon, commonly referred to as Arctic amplification, and its peak in boreal fall and winter result primarily from the so-called lapse-rate feedback, which is associated with the vertical structure of tropospheric warming, rather than from the sea-ice albedo feedback, which operates mainly in boreal summer. However, future climate model projections show consistently that an overall reduction of sea-ice in the Arctic region leads to a gradual weakening of Arctic amplification, thereby implying a key role for sea-ice albedo feedback. To resolve this apparent contradiction, a new study accepted in Earth’s Future conducted a comprehensive analysis using atmosphere-ocean reanalysis datasets and a variety of climate model simulations. This study showed that the Arctic Ocean acts as a heat capacitor, storing anomalous heat resulting from the sea-ice loss during summer, which is then released back into the atmosphere during fall and winter. The ocean heat-driven strong air-sea heat fluxes in fall and winter in sea-ice retreat regions in conjunction with a stably stratified lower troposphere lead to a surface-intensified warming and moistening, augmenting longwave feedback processes to further enhance the pronounced Arctic warming in the cold season. These results strongly suggest that the warm-season ocean heat recharge and cold-season heat discharge link and integrate the warm and cold season feedbacks, and thereby effectively explain the predominance of the Arctic amplification in fall and winter.
Figure 8 from Chung et al. (2020): A schematic diagram illustrating the contribution of anomalous seasonal ocean heat uptake and release to fall and winter Arctic amplification. The upper ocean stores heat resulting from GHG-induced sea-ice loss during summer, and the accumulated heat is then released back into the atmosphere during fall and winter. Due to a stable condition in the lowermost part of the atmosphere during the cold season, a large fraction of the heat and moisture released from sea-ice retreat regions is trapped in that layer. The surface-intensified warming and moistening in turn acts to further promote LW feedback processes, including the lapse-rate feedback, to enhance the warming.
Chung, E.S., Ha, K.J., Timmermann, A., Stuecker, M.F., Bodai, T., & Lee, S.-K. (2020). Cold‐Season Arctic Amplification Driven by Arctic Ocean‐Mediated Seasonal Energy Transfer. Earths Future, 8, e2020EF001898 https://doi.org/10.1029/2020EF001898.