Petermann Glacier on the brink: Progress, challenges and insights.

Petermann Glacier (PG), the largest marine-terminating glacier in northern Greenland based on catchment area and ice discharge, plays a key role in modulating ice export from the Greenland Ice Sheet (GrIS). With an upstream catchment connected to the GrIS interior via a deep subglacial canyon, its future stability has major implications for sea level rise. This review synthesizes recent advances in understanding PG's dynamics across three critical interfaces. At the surface, reanalysis data and regional climate models diverge from observations in estimates of air temperature and surface mass balance, underscoring the need for improved in situ data and models. At the ocean boundary, enhanced basal melting driven by subglacial runoff and Atlantic water intrusions is identified as dominant driver of recent mass loss of PG, with continued warming posing a serious threat to the stability of the floating tongue. At the bed, geophysical synthesis reveals complex geology, likely spatial variability in geothermal heat flux, and the megacanyon's influence on seasonal hydrology and velocity fluctuations. An ongoing rifting event, initiated in September 2025, highlights PG's vulnerability. The anticipated retreat reduces buttressing and brings the terminus closer to the grounding zone, where additional calving could trigger retreat and accelerate ice discharge. As one of Greenland's largest floating ice tongues, PG may provide important insights into the stability of other marine-terminating glaciers across the GrIS. Improved observations, sustained monitoring of oceanographic and atmospheric parameters, and high-resolution modeling are critical for constraining projections of PG's future and its role in GrIS stability.