Most climate models neglect cloud longwave (LW) scattering because scattering is considered negligible compared to strong LW absorption by clouds and greenhouse gases. While this rationale is valid for simulating extra‐polar regions, it is questionable for the polar regions, where the atmosphere is dry and hence has weak absorption, and ice clouds that have strong scattering capability frequently occur. Using the slab‐ocean Community Earth System Model, we show that ice cloud LW scattering can warm winter surface air temperature by 0.8‐1.8K in the Arctic and 1.3‐1.9K in the Antarctic, while this warming becomes much weaker in polar summer. Such scattering effect cannot be correctly assessed when sea surface temperature and sea ice are prescribed as its effect is manifest through a surface‐atmosphere coupling. Cloud longwave scattering is a necessity for the correct simulation of polar climate and surface radiation budget, especially in the winter.