<p>Accelerated Arctic warming exhibits pronounced seasonality, with the strongest amplification during the cold seasons (autumn, winter, and spring) and the weakest warming in summer. Yet a unified physical explanation for this contrast remains unclear. Here we present a process-based, seasonally resolved quantification of recent Arctic warming by jointly diagnosing changes in near-surface air temperature, surface temperature, and atmospheric moisture within a unified framework. Two fundamentally distinct seasonal warming regimes emerge. In summer, near-surface air warming is weak and primarily governed by adiabatic heating. Surface warming is driven mainly by increased net shortwave radiation associated with sea ice–albedo feedback, with a secondary contribution from downward longwave radiation. Nearly 86% of the additionally absorbed energy is sequestered in subsurface processes (e.g., sea-ice melt and upper-ocean heat uptake), suppressing upward turbulent heat fluxes and limiting surface–atmosphere coupling. Summertime atmospheric moistening arises predominantly from enhanced poleward water vapor transport and acts primarily as a radiative amplifier of surface warming, without establishing a strong local thermodynamic feedback for atmospheric warming. In contrast, cold-season warming is controlled by a tightly coupled thermodynamic regime centered on moisture processes. Increased atmospheric water vapor enhances downward longwave radiation, warms the surface, strengthens upward turbulent heat fluxes, and drives lower-tropospheric diabatic heating. Subsurface heat release further reinforces this warming. Together, these processes establish a positive moisture–radiation–turbulence feedback that efficiently amplifies both surface and near-surface air temperatures. This seasonally differentiated framework provides a physically consistent explanation for the observed seasonality of accelerated Arctic warming and offers a process-oriented benchmark for climate model evaluation.</p>