Trends and variability in the Southern Annular Mode over the Common Era
Reconstructing the Southern Annular Mode over the last 2,000 years to better understand southern hemisphere climate dynamics.
In this paper, we use data assimilation to reconstruct the Southern Annular Mode (a major climate pattern) over the last 2,000 years. Specifically, we use an ensemble Kalman filter to integrate a multi-model ensemble of historical global climate model runs with the 20th century reanalysis (20CR), Pages2k collection, the South American Drought Atlas (SADA), and the Australia-New Zealand Drought Atlas (ANZDA). We find no evidence for a forced response in SAM variability prior to the 20th century. By contrast, we do find the modern positive trend falls outside the 2σ range of the prior 2000 years at multidecadal time scales. This latter finding supports the inference that the SAM’s positive trend over the last several decades is a response to anthropogenic climate change.