Abstract Arctic amplification (AA), referring to the greater warming of the Arctic relative to lower latitudes, is a robust feature in observations and in climate model simulations driven by increasing greenhouse gases. In this study, we examine the rapid development of AA following abrupt CO2 quadrupling in CMIP5 and CMIP6 models. We show that this rapid development of AA is a consequence of the Arctic’s lower effective heat capacity compared to the tropics and global mean. The Arctic’s lower heat capacity, which is due to the presence of sea ice, leads to polar‐amplified warming in response to CO2 radiative forcing alone. However, the full magnitude of AA can only be understood by also considering the feedbacks and energy transport changes that act to preferentially warm the Arctic region.

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