On the Arctic Amplification of surface warming in a conceptual climate model

Abstract

Over the last century Earth's surface temperatures have warmed by order 1 K as a global average, but with significant variation in latitude: there has been most surface warming at high Northern latitudes, around 3 times more than in low latitude regions (termed Arctic Amplification), while there has been least warming over the Southern Ocean. Many contributing processes have been suggested to explain this asymmetrical latitudinal warming pattern, but quantification of the contributing factors responsible remains elusive. Complex general circulation climate models can reproduce similar asymmetrical patterns of warming, but it can be difficult to interpret the contributing processes. Meanwhile, idealised conceptual energy balance climate models have been able to reproduce a general polar amplification of warming whose origins can be interpreted, but this warming is often symmetrical across both hemispheres and may not be responsible for the real-world pattern. Here, we use a conceptual Energy Balance Model, with imposed closures for initial horizontal diffusivity and cloudiness drawing upon observational constraints and including temperature-dependent diffusivity and a sub-surface ocean heat reservoir, to show that the magnitude of present-day Arctic Amplification may arise through relatively simple thermodynamic (Clausius–Clapeyron) and radiative (climate feedback) processes. The current asymmetry between hemispheric warming may arise due to the transient heat transport up through the base of the surface ocean mixed layer from the slow-responding deep ocean to the fast-responding surface ocean being dominated by upwelling in the Southern Ocean. It should be noted that the processes identified here are not a unique in offering a potential solution, and so significant, or dominant, roles for dynamical processes remain plausible explanations for Arctic Amplification.