Ice-core-based reconstructions show that increased snow accumulation on the Antarctic Ice Sheet mitigated global sea level rise by ~ 10 mm during 1901-2000 (Medley and Thomas, 2019). Here, we attribute this trend by evaluating a suite of single-forcing, all-forcing and nudged ensembles from a climate model, along with dynamically consistent reconstructions of sea level pressure, temperature and wind from paleoclimate data assimilation (PDA). The single-forcing ensembles reveal that rising concentrations of greenhouse gasses (GHGs) have been the dominant driver of the historical snow accumulation increase, but acting alone, GHGs would have caused twice the observed increase. We investigate possible explanations for this over-prediction: a) The uncertain cooling effects of anthropogenic aerosols; b) Extreme internal variability; c) Atmospheric circulation trends; and d) Sea surface temperature (SST) trends evident in the PDA reconstructions (and observed SSTs) but not simulated by the model. The latter best explains the spatial and temporal evolution of snow accumulation, including the lack of an Antarctic-wide accumulation increase since 1980. This SST trend pattern resembles the previously modeled response to Antarctic meltwater, and its emergence coincides with the mid-Twentieth-Century onset of ice shelf thinning and retreat of Thwaites and Pine Island glaciers. Aerosols have also damped the accumulation increase and contributed to the global-scale SST pattern, which includes long-term cooling in the central tropical Pacific that cannot be explained by internal variability. Our results imply that including Antarctic meltwater in models would substantially improve projections of Antarctic snowfall, global sea level, and SSTs in the Southern Ocean and tropical Pacific.