The recent emergence of Arctic Amplification

Arctic Amplification in response to climate forcing is a robust and pervasive phenomenon found in a wide range of climate model simulations and in the paleoclimate record. Here, we investigate to what extent - and why - Arctic Amplification has occurred over the last century in the observational record. We show that Arctic Amplification is a relatively recent phenomenon, only occurring in 50-year trends starting from 1950. In fact, we find that for much of the 20^th century, the Arctic cooled while global-mean temperature showed a small warming trend. We analyze large ensembles of comprehensive climate model simulations, as well as single-forcing ensembles, to quantify the contributions of greenhouse gases, industrial aerosols, and internal climate variability to the observed trends.