Ice Shelves An unusually warm and prolonged inflow of warm ocean water intruded beneath Antarctica's Filchner Ronne Ice Shelf in 2017. Ryan et al. describe a 4-year-long time series of ocean temperature measurements that documents the surge and its unusual persistence. They discuss the hydrographic properties of the event and possible forcing mechanisms, suggesting that it was caused by anomalous summer sea ice melting. Much of the thinning of ice shelves like the Filchner Ronne is caused by warm water intrusions. Similar intrusions beneath other ice shelves will affect the future stability of the Antarctic Ice Sheet, a pressing concern in our warming climate. Geophys. Res. Lett. 10.1029/2020GL088119 (2020).