Polar amplification is a robust feature of past and future warm climates, yet its hemispheric asymmetry and underlying mechanisms remain poorly understood in deep-time climate states. The Miocene Climatic Optimum (MCO, ca. 16.9–14.75 Ma) represents a warm interval under elevated CO₂ concentrations (~400–600 ppm), offering an analog for future climate warming. Here, using the fully coupled general circulation model FGOALS-g3 with Miocene boundary conditions, we investigate the mechanisms underlying asymmetric polar amplification between two hemispheres. We find that Arctic amplification exceeds Antarctic amplification. This asymmetry arises from the atmosphere–sea ice interactions, rather than from differences in effective climate sensitivity to CO₂ forcing. Energy budget diagnostics and radiative kernel analysis indicate that, net Arctic warming is amplified primarily by stronger surface albedo feedback, followed by stronger lapse rate feedback. In contrast, weaker positive feedbacks and atmospheric heat convergence lead to more moderate Antarctic warming. These findings underscore the critical role of large-scale energy redistribution and hemispheric boundary conditions in shaping polar climate sensitivity and provide new mechanistic insights into asymmetric polar warming during the Miocene.

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