Dynamical Amplifier of Thermodynamical Radiative Forcings and the High-latitude Surface Warming (formerly paper JP6.7)

The recent Arctic Climate Impact Assessment reports that “annual average arctic temperature has increased at almost twice the rate as the rest of the world over the past few decades”. Furthermore, the rapid surface warming in high-latitudes is particularly strong in winter. Local thermodynamical feedbacks act to amplify the surface warmings in high latitudes more strongly than the low-latitude warmings. We here present theoretical, observational, and modeling evidences suggesting that the dynamical poleward heat transport feedbacks may further amplify the enhanced high-latitude surface warmings due to each individual thermodynamical feedbacks in response to an anthropogenic radiative forcing. It can be shown that as a result of an enhanced poleward heat transport due to an anthropogenic radiative forcing, part of the extra amount of thermal energy intercepted by the low-latitude atmosphere due to an increase in its opacity is transported to high latitudes. This effectively implies a “greenhouse-plus” (“greenhouse-minus”) feedback to the high (low) latitude surface temperatures, thereby amplifying (weakening) the direct response to the anthropogenic radiative forcing in high (low) latitudes. The non-local dynamical feedbacks and local ice-albedo feedbacks are strongest in winter whereas local thermodynamical feedbacks associated with water cycle are dominant in summer. Due to the suppression of the negative dynamical feedback in low-latitudes by the Stefan-Boltzmann feedback, the net dynamical feedbacks also further amplify the global mean surface temperature warmings.

For an anthropogenic radiative forcing of 4Wm-2 in a simple moist radiative-transportive coupled atmosphere-land/ocean model, the dynamical amplifier yields an additional surface warming of 0.64 K in high latitudes in winter season on top of the 1.24K warming due to sum of the anthropogenic radiative forcing and all local thermodynamic feedbacks. It also adds a 0.16K warming to the global surface warming of 1.27K due to the direct and indirect thermodynamic forcings.