Trends and Variability in the Southern Annular Mode over the Common Era

The Southern Annular Mode (SAM) is the leading mode of atmospheric variability in the extratropical Southern Hemisphere and has wide ranging effects on ecosystems and societies. Despite the SAM’s importance, paleoclimate reconstructions disagree on its variability and trends over the Common Era, which may be linked to variability in SAM teleconnections and the influence of specific proxies. Here, we use data assimilation with a multi-model prior to reconstruct the SAM over the last 2000 years using temperature and drought-sensitive climate proxies. Our method is not calibrated directly to the SAM index and does not assume a stationary relationship between the SAM and the local climates recorded by the proxy records. Our approach also allows us to identify critical paleoclimate records and quantify reconstruction uncertainty through time.  We find no evidence for a forced response in SAM variability prior to the 20th century. We do find the modern positive trend is outside the range of the prior 2000 years at multidecadal time scales, supporting the inference that the positive trend in the SAM over the last several decades is a response to anthropogenic climate change.