Local and Non-⁠local Mechanisms of Polar Amplification

Abstract:

Polar amplification (PA) is a prominent feature of currently observed and predicted future climate change suggested by both observations and models. Surface albedo feedback (SAF) has been shown to contribute prominently to the currently observed PA along with other mechanisms, e.g. involving atmospheric heat transport. SAF is believed to be a strong positive local feedback, while the atmospheric heat transport makes the connection between the Arctic and the low latitudes non-local. We will discuss several PA mechanisms and feedbacks suggested by different researchers. We will also discuss a more general method of feedback analysis that results in feedback and gain matrices. These matrices generalize (both globally and locally) the classically defined numerical gains and feedback factors and are independent of the applied forcing. The gain matrix, in particular, is shown to reveal, under any forcing scenario, the global pattern by which a given feedback process amplifies or dampens fixed-feedback temperature anomalies. Moreover, in the case of a feedback process that is not purely a function of local temperature, these matrices will show the degree to which this "local feedback process" depends on non-local perturbations. We apply this method in the context of a simple box model as well as a one-dimensional energy balance climate model.