Dynamical amplification of polar warming

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 pronounced in winter. Local thermodynamic feedbacks can contribute to a relatively larger surface warming in high latitudes through the ice-albedo feedback that amplifies the high latitude warming and through the evaporation feedback that more strongly damps the low latitude surface warming. The global surface warming is also amplified by the water vapor feedback. We present theoretical evidences suggesting that the poleward heat transport is one of the most fundamental processes causing the polar warming amplification. In essence, the dynamical amplifier acts as a “greenhouse-plus” feedback to the polar warming by transporting poleward (i) part of the extra energy intercepted by the low-latitude atmosphere and (ii) part of the thermal energy due to local thermodynamical feedbacks, leading to an amplified high latitude warming. For an anthropogenic radiative forcing of 4 Wm?2, we illustrate that the dynamical amplifier contributes to about 1/3 (1/10) of the total high-latitude (global) surface warming in winter in a simple coupled atmosphere-surface radiative-transportive climate model. Budget analysis of the radiation flux at the top of the atmosphere derived from IPCC AR4 CGCM climate simulations supports the dynamical amplifier theory for the larger warming in high latitudes.