The Polar Amplification Asymmetry: Role of Antarctic Surface Height

Previous studies have attributed an overall weaker (or slower) polar amplification in the antarctic compared to the arctic region to a weaker surface albedo feedback in the antarctic compared to the arctic region and to more efficient ocean heat uptake in the southern ocean compared to the Arctic in combination with antarctic ozone depletion. Here, the role of antarctic surface height for meridional heat transport and local radiative feedbacks is investigated based on CO₂ doubling experiments in a low resolution coupled climate model. If Antarctica is assumed to be flat, the north-south asymmetry of the zonal mean top of the atmosphere radiation budget is significantly reduced. Doubling CO₂ in a flat Antarctica (``flat AA'') model setup leads to a stronger increase of southern hemispheric poleward atmospheric and oceanic heat transport compared to the base model setup. Based on partial radiative perturbation computations it is shown that local radiative feedbacks and an increase of the CO₂ forcing in the deeper atmospheric column contribute to stronger antarctic warming in the flat AA model setup, and the roles of the individual radiative feedbacks are discussed in some detail. A significant fraction (between 24 and 80% for three consecutive 25-year time slices starting in year 51 and ending in year 126 after CO₂ doubling) of the  polar amplification asymmetry is explained by the difference in surface height, but the fraction is subject to transient changes, and might to some extent also depend on model uncertainties such as the ones related to cloud feedbacks. Assuming a flat Antarctica not only influences Antarctica, but also Arctic amplification.