Recent Observations of Thwaites Glacier, West Antarctica Are Consistent With High Rates of Loss in Next 50 Years

Abstract Thwaites Glacier has experienced accelerating mass loss, with rates increasing over fivefold since the 1990s. We apply transient calibration to two independent ice‐sheet models (STREAMICE and ISSM) using time‐varying velocity and surface elevation data from 2004 to 2017 to project future mass loss through 2067. We test different calibration approaches: constraining to velocities only, surface elevation change only, or both combined. Models calibrated solely to surface elevation change show the best agreement with observed volume‐above‐floatation loss rates and project the largest future mass losses, reaching 180–200 Gt/a by 2067—comparable to current Antarctic‐wide mass balance. These surface‐constrained models produce focused thinning patterns extending ∼100 km inland along Thwaites' deep trough, suggesting potential marine ice sheet instability. In contrast, velocity‐only calibrations show initially high but rapidly stabilizing loss rates. Our results demonstrate that calibration methodology critically influences century‐scale projections, with surface‐elevation‐constrained models providing the most realistic representation of observed dynamical changes.