Geophys. Res. Lett. (2020)

Arctic temperatures are increasing at more than twice the global rate. This is attributed in part to the surface albedo feedback, in which melting of snow and ice exposes the underlying land and ocean, and these darker surfaces absorb more sunlight and amplify warming. Changes in the atmospheric temperature structure and moisture content, as well as enhanced northward heat transport into the Arctic Ocean, are also at play, although the oceanic mechanism is not well understood.

Emma Beer at the Scripps Institution of Oceanography, University of California San Diego, USA and colleagues use an idealized climate model to study ocean-driven Arctic amplification. In response to long-term greenhouse gas forcing, the Arctic Ocean warms at depth, but where sea ice persists, the near-surface waters remain close to freezing. The authors find that these changes cause a larger vertical temperature gradient in the ocean, enhance vertical and horizontal heat flux, and thin the sea ice above. This mechanism evolves seasonally and, paradoxically, highlights a route for Arctic amplification that relies on the presence of sea ice rather than its absence.