Research results and new frontiers for the International Thwaites Glacier Collaboration, 2018-2024

The evolution of Thwaites Glacier represents the largest uncertainty in sea level rise forecasts over the next few centuries. To address this concern, the International Thwaites Glacier Collaboration (ITGC) was co-sponsored by the US and UK polar research agencies with contributions from Sweden, Germany, and South Korea. The program investigated all aspects of the climate-ice-ocean-earth system in the Thwaites-Amundsen region, in eight coordinated projects. Several of the scenarios of highest concern for rapid increase in ice flux from the system are found to be less likely than initially thought. However, newly discovered processes that could accelerate ice loss, and additional considerations of the processes investigated, mandate that the region receive continued focus. Modelling and observational data show that the impending loss of the remaining ice shelf will result in only a small (order 10%) increase in grounded glacier flow speed, at least initially. Runaway ice cliff failure, while a valid process with several forms, is difficult to sustain in model scenarios so far; however, concerns remain about the effects of damaged ice on the ice-cliff calving thresholds and rates. Studies of the Holocene and recent pre-satellite evolution of the system show that the region has experienced very rapid retreat in the recent past, and that ice elevation near the Holocene Optimum was around 35 m lower than the present day, but then recovered as climate slowly cooled and bed elevation increased due to glacial isostatic adjustment to ice loss following the Last Glacial Maximum. Modern retreat at the Thwaites and Pine Island glaciers appears to have been initiated in the 1940s after a series of very strong El Niño–Southern Oscillation (ENSO) effects. In considering the future retreat and ice loss from the Thwaites catchment, studies of the shear margins and bed imply that further ice loss will likely widen the glacier, and that the pattern of mixed resistant and slick bed conditions will actually lead to slightly faster retreat of the Thwaites  Glacier basin in the coming centuries. Lastly, significant concerns remain about a tidal pumping process, inferred from satellite and field observations as part of the project, that may be driving warm near-bottom seawater several kilometers upstream of the nominal grounding line. This process, and in general the oceanography near the ice front and basal geology of the glacier bed, remain areas in need of continuing study by the community.