Antarctic heatwaves driven by atmospheric rivers are emerging as high-impact extremes, yet the role of climate change in amplifying such events remains uncertain. Here we investigate the climate change contribution to the March 2022 East Antarctic heatwave using pseudo-global warming experiments with the snow-atmospheric coupled model CRYOWRF. By comparing present-day and preindustrial storylines, we identify that under current climate, cloud and water-vapor radiation feedbacks non-linearly amplify near-surface warming by up to 25% relative to preindustrial conditions. These feedbacks are likely underrepresented in global climate models due to their use of hydrostatic dynamics, and poor cloud representation over coarse resolutions. Future warming further intensifies this amplification, particularly in coastal regions where firn air content is depleted, meltwater percolates, and ice lenses thicken. Such melting conditions threaten to accelerate surface mass loss and destabilize the fringing ice shelves. Our results reveal a key amplification pathway for Antarctic extremes, with potentially far-reaching implications for ice-sheet stability.