Simple Estimates for Polar Amplified Warming

The amplification of radiatively forced surface temperature change at high latitudes has been a ubiquitous feature of climate change projections since early general circulation model (GCM) simulations, and an extensive literature using GCM simulations to assess the mechanisms underlying this polar amplified warming now exists. Here, we aim to address the following order-of-magnitude question: why do climate change simulations feature polar warming that is a factor of two-to-three larger than that of lower latitudes rather than a much larger (e.g., 10 times) or smaller factor? We present simple estimates for polar amplified warming that do not require GCM simulations to provide easy-to-interpret, though approximate, answers to the order-of-magnitude question.