Sack Lunch Seminar (SLS)

Much can be learned about climate by measuring how it responds to an impulsive forcing. Climate Response Functions (CRF) to Greenhouse gas (GHG) forcing are commonly computed from models and used to characterize the role of atmospheric feedbacks and ocean heat uptake in modulating the amplitude and timing of surface warming. Here we propose a similar strategy to study the response of the climate around Antarctica to an ozone hole which is instantaneously turned on and taken through a repeating seasonal cycle. Unlike GHG forcing whose influence is predominantly thermodynamic at the sea surface, ozone hole forcing is primarily mechanical and associated with its projection on to the surface windstress that covaries with the Southern Annular Model (SAM). The form of the Ozone Hole CRF is studied in a simple coupled model and shown to initially comprise a dipole in SST with cooling around Antarctica and growth of sea-ice with warming further north. Over time, however - order a decade - the dipole evolves in to a monopole as warm water from the subsurface ocean is upwelled to the surface leading to a retreat in sea-ice. We discuss the contrast between the GHG and Ozone Hole Response functions and how they might be used to understand recent trends in Antarctic surface temperature and sea-ice.