Strong Ocean Melting Feedback During the Recent Retreat of Thwaites Glacier

Accelerating ice loss from Thwaites Glacier is contributing approximately 5% of global sea-level rise, and could add tens of centimeters to sea level over the coming centuries. We use an ocean model to calculate sub-ice melting for a succession of Digital Elevation Models of the main trunk of Thwaites Glacier from 2011 to 2022. The ice evolution during this period induces a strong geometrical feedback onto melting. Ice thinning and retreat provides a larger melting area, thicker and better-connected sub-ice water column, and steeper ice base. This leads to stronger sub-ice ocean currents, increasing melting by over 30% without any change in forcing from wider ocean conditions. This geometrical feedback over just 12 years is comparable to melting changes arising from plausible century-scale changes in ocean conditions and subglacial meltwater inflow. These findings imply that ocean-driven ice loss from Thwaites Glacier may only be weakly influenced by anthropogenic emissions mitigation.