The seabed ridge that holds Thwaites is the key variable

The narrow place holding the ice

The fast western trunk of Thwaites Glacier still meets a ridge on the seabed. As seawater intrudes beneath ice that otherwise rests on the bed, the contact zone shifts. A new peer reviewed model represents that transition as an actively melting region several kilometres wide, rather than a sharp line. The physical question is therefore where ocean water can reach the ice, as well as how much heat the ocean supplies.^[1]

The researchers compared simulations with satellite evidence from 1996–2023, testing retreat, thinning and acceleration together. Configurations that match those histories use a seawater intrusion zone 2–5 kilometres wide and basal melt rates of 90–120 metres a year. Versions without the active zone were much less successful at reproducing all three changes at once. That historical comparison gives a concrete test of how long the seabed ridge may restrain the glacier.^[1]

The scenario beyond the ridge

When the calibrated model is run forward, some configurations unpin the ice from the ridge as early as 2038. The study projects up to 30.1 ± 5.7 millimetres of contribution to global mean sea level for 2100, roughly twice the comparison projections. These are conditional model results, not a measured rise or a fixed timetable. The difference matters to assessments of coastal exposure, although this global mean figure cannot by itself specify a particular shoreline’s water level.^[1]

The forward experiment holds climate forcing at a historical average to isolate melting at the ice bed. It leaves future ocean warming outside this test, so its number is not an upper bound for every climate pathway. My reading is that ice sheet assessments need to test intrusion explicitly. Adjusting only a melt rate can create an apparent fit while missing the historical thinning and acceleration that the model must explain together.^[1]

The next measurement

The model’s limits also sit at the contact zone. The researchers adjusted local seabed elevation beneath the eastern ice shelf to reconcile the initial geometry with observations. They did not explicitly calculate how seawater lubrication changes friction beneath grounded ice. Both the mapped seabed and that omitted process can affect the retreat path. A single unpinning year or millimetre total therefore carries more uncertainty than its crisp numeral suggests.^[1]

The useful next check is to observe intrusion length, basal melt, ice speed and the grounding zone together at the same ridge. New satellite passes can show temporary lifting; later comparisons can test whether it turns into sustained retreat. For coastal planning, this is a practical modelling lever: projections improve when the physics of how ice holds onto its bed is represented and tested against multiple measurements.^[1]