Influence of Surface Types on the Seasonality and Inter-Model Spread of Arctic Amplification in CMIP6

A robust phenomenon termed the Arctic Amplification (AA) refers to the stronger warming taking place over the Arctic compared to the global mean. The AA can be confirmed through observations and reproduced in climate model simulations and shows significant seasonality and inter-model spread. This study focuses on the influence of surface type on the seasonality of AA and its inter-model spread by dividing the Arctic region into four surface types: ice-covered, ice-retreat, ice-free, and land. The magnitude and inter-model spread of Arctic surface warming are calculated from the difference between the abrupt-4 × CO₂ and pre-industrial experiments of 17 CMIP6 models. The change of effective thermal inertia (ETI) in response to the quadrupling of CO₂ forcing is the leading mechanism for the seasonal energy transfer mechanism, which acts to store heat temporarily in summer and then release it in winter. The ETI change is strongest over the ice-retreat region, which is also responsible for the strongest AA among the four surface types. The lack of ETI change explains the nearly uniform warming pattern across seasons over the ice-free (ocean) region. Compared to other regions, the ice-covered region shows the maximum inter-model spread in JFM, resulting from a stronger inter-model spread in the oceanic heat storage term. However, the weaker upward surface turbulent sensible and latent heat fluxes tend to suppress the inter-model spread. The relatively small inter-model spread during summer is caused by the cancellation of the inter-model spread in ice-albedo feedback with that in the oceanic heat storage term.