Anthropogenic and internal drivers of wind changes over the Amundsen Sea, West Antarctica, during the 20th and 21st centuries

Ocean-driven ice loss from the West Antarctic Ice Sheet is asignificant contributor to sea-level rise. Recent ocean variability in theAmundsen Sea is controlled by near-surface winds. We combine palaeoclimatereconstructions and climate model simulations to understand past and futureinfluences on Amundsen Sea winds from anthropogenic forcing and internalclimate variability. The reconstructions show strong historical wind trends.External forcing from greenhouse gases and stratospheric ozone depletiondrove zonally uniform westerly wind trends centred over the deep SouthernOcean. Internally generated trends resemble a South Pacific Rossby wavetrain and were highly influential over the Amundsen Sea continental shelf.There was strong interannual and interdecadal variability over the AmundsenSea, with periods of anticyclonic wind anomalies in the 1940s and 1990s,when rapid ice-sheet loss was initiated. Similar anticyclonic anomaliesprobably occurred prior to the 20th century but without causing the presentice loss. This suggests that ice loss may have been triggered naturally inthe 1940s but failed to recover subsequently due to the increasingimportance of anthropogenic forcing from greenhouse gases (since the 1960s)and ozone depletion (since the 1980s). Future projections also featurestrong wind trends. Emissions mitigation influences wind trends over thedeep Southern Ocean but has less influence on winds over the Amundsen Seashelf, where internal variability creates a large and irreducibleuncertainty. This suggests that strong emissions mitigation is needed tominimise ice loss this century but that the uncontrollable future influenceof internal climate variability could be equally important.