Decoded Antarctic snow accumulation history reconciles observed and modeled trends in accumulation and large-scale warming patterns

Increased snow accumulation on the Antarctic Ice Sheet mitigated global sea level rise by ∼ 11 mm during 1901–2000 according to ice core reconstructions. However, in the most recent 40 years of more intense observation and warming, the trend in the Antarctic-wide accumulation rate has been negligible. We attribute these trends by evaluating Earth system model experiments in comparison with dynamically consistent reconstructions of surface climate. Single-forcing experiments reveal that rising concentrations of greenhouse gases (GHGs) have been the underlying driver of increased accumulation, yet acting alone would have caused twice the observed accumulation-related sea level mitigation during 1901–2000. Aerosol-driven cooling partially compensates this overprediction, but the reconstructions provide evidence that poorly modeled processes can explain observation-model trend discrepancies. In particular, these data support a hypothesis that high-latitude winds have been working together with ice-shelf meltwater fluxes to dampen Southern Ocean surface warming and suppress the GHG-driven accumulation increase since the initiation of West Antarctic ice shelf thinning in the mid-20th Century. The wind pattern associated with strengthening of the Southern Hemisphere westerlies and deepening of the Amundsen Sea Low distributes accumulation unevenly across the continent in an orographic pattern that is consistent across models and the reconstructions. In reconstructions, these same wind and accumulation patterns are associated with muted surface warming across the eastern Pacific and Southern Ocean, a pattern not captured in climate projections including the all-forcings large ensemble studied here. However, the westerly wind history constrained by paleoclimate data assimilation largely reconciles differences between the model's ensemble-mean response and the observed world for both Antarctic-wide accumulation and large-scale warming patterns. Although the large ensemble simulates similar wind histories to the real one – driven by internal variability and anthropogenic forcing – its corresponding responses in SSTs and Antarctic-wide snow accumulation are decoupled from the wind. We discuss how this significant observation-model discrepancy, which has implications for projecting regional climate change, likely arises from omitted meltwater forcing and/or resolution limitations. As a component of the sea level budget and a gauge of the magnitude and spatial pattern of climate change, Antarctic snow accumulation is a critical target for models to replicate.