The Southern Annular Mode and its relationship with Antarctic temperature in contrasting future storylines

The Southern Annular Mode (SAM) strongly modulates Antarctic near-surface air temperature (SAT) variability. We employ a storyline approach to examine projected end of century changes in the spatial SAM-SAT relationship across Antarctica in two models from the sixth phase of the Coupled Model Intercomparison Project (CMIP6) under a high end forcing Shared Socioeconomic Pathway (SSP5-8.5) for both austral winter and summer. The models represent a pair of climate storylines (termed B and C as in previous work) corresponding to plausible future physical changes in two remote drivers. Relative to the CMIP6 multi-model mean response, Storyline B is characterised by high seasonal sea ice extent loss and either low stratospheric polar vortex (SPV) strengthening in winter or early SPV breakdown in summer: Storyline C is distinguished by opposing projected changes. Our analysis demonstrates that deviations in the future SAM-SAT relationship are markedly greater between the two storylines in summer, when significant differences occur across much of Antarctica, than in winter. The greater differences in summer arise because Storyline B exhibits a less positive (more negative) relationship between the SAM and SAT across the Antarctic Peninsula (West Antarctica), in contrast to a less negative SAM-SAT relationship in East Antarctica: opposing changes are observed for Storyline C. Disparities in the former regions can be traced to differences in the location and strength of the climatological Amundsen Sea Low. This work highlights the use of the storyline approach to establish the spread of credible regional Antarctic climate responses across a single climate change scenario.