Large scale climate response of the Southern Ocean and Antarctica to reduced ice sheets
Abstract. The Antarctic and Greenland Ice Sheets (AIS and GIS) are critical tipping points in the Earth's climate system. Their potential collapse could trigger cascading effects, significantly alter the global climate patterns, and cause large-scale, long-lasting, and potentially irreversible changes within human timescales. This study investigates the large-scale climate response of the Southern Ocean and Antarctica to the isolated effect of reducing ice sheet extent. Using well-documented paleogeography of the Late Pliocene (LP) from the PRISM4D reconstruction, where the West Antarctic Ice Sheet (WAIS) and the northwestern GIS were significantly diminished, we conducted 1450-year simulations with the EC-Earth3 model at atmospheric CO2 concentrations of 280 ppmv and 400 ppmv.
Our results reveal that the implementation of the LP ice sheet configuration leads to a 9.5 °C rise in surface air temperature, approximately 16 % reduction in sea ice concentration, and a 0.63 mm/day increase in precipitation over Antarctica and the Southern Ocean. These changes far exceed those driven by CO2 increase alone, which result in a 2.5 °C warming and a 9.3 % sea ice decline. Throughout the simulations, the positive phase of the Southern Annular Mode (SAM) persists, intensifying westerly winds and contributing to sea ice export and deep ocean warming. The combined effects of ice sheet reduction and CO2 forcing initially weakened Antarctic Bottom Water formation, with major implications for the Global Meridional Overturning Circulation due to stronger water column stratification driven by surface freshening and subsurface warming.
By isolating the direct albedo effect of reducing GIS and AIS extents, this study offers critical insights into the mechanisms driving atmospheric and oceanic variability around Antarctica and their broader implications for global climate dynamics. Although the complete Late Pliocene boundary conditions may serve as a valuable analogue for current and future climate change, excluding the orographic changes allows us to specifically assess the primary role of surface reflectivity. This targeted approach lays the groundwork for future research to explore how the combined effects of albedo and paleogeographical changes could influence interhemispheric climate feedbacks under scenarios of future ice sheet collapse or instability.