A new ice-sheet model indicates that seawater is reaching beneath grounded ice at Thwaites Glacier much farther inland than older models allowed. That overlooked tidal process could make Thwaites contribute up to 1.2 inches (about 30 millimeters) to global sea-level rise by 2100 under a no-additional-warming assumption—roughly twice earlier estimates.
What the new Thwaites Glacier study found
Thwaites Glacier in West Antarctica is already losing ice and is one of the most important sources of present-day sea-level rise. A report published October 15, 2026, describes a UC Irvine and NASA Jet Propulsion Laboratory model that changes how the glacier’s grounding line is represented.
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The grounding line is the transition where ice resting on the seafloor begins to float as an ice shelf. Older large-scale models generally treated that boundary as a relatively narrow, fixed line. The revised approach treats it as a tide-driven grounding zone that can extend for kilometres and move back and forth with the tides.
Do these 3 things before closing this tab:
1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsIn the model, seawater can flush beneath ice that is still grounded. That circulation carries relatively warm Southern Ocean water inland, increases melting at the glacier’s base and reduces the area where ice remains firmly attached to the bed. The result is a modeled Thwaites contribution of up to 1.2 inches (approximately 30 millimeters) of global sea-level rise by 2100, even without additional global warming. The report says that is about twice earlier estimates.
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Lead author Mattia Poinelli said scientists “have come to acknowledge a different arrangement beneath Earth’s major ocean-terminating glaciers.”
Why a mobile grounding zone changes the physics
Tidal pumping moves seawater inland
As tides rise and fall, the grounding zone can lift and settle. That motion opens pathways for seawater to migrate beneath grounded ice rather than stopping at the old grounding-line position. Daily-repeat ICEYE satellite radar interferometry collected from March through June 2023 documented this seawater movement beneath grounded Thwaites ice.
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Warm water reaches more ice
Southern Ocean water is relatively warm compared with the ice and seawater at the glacier’s base. If it reaches farther inland, basal melting can occur across a broader area than models that omit tidal intrusion represent. Less contact with the bed also means less friction resisting flow toward the ocean.
Retreat exposes thicker ice
The bed beneath Thwaites slopes downward inland. As the grounding zone retreats, the glacier can expose thicker ice to ocean influence, creating a process that can accelerate retreat rather than simply moving it at a constant rate.
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The numbers readers need to keep separate
| Measure | What it means | Qualification |
|---|---|---|
| Up to 1.2 inches (30 mm) by 2100 | Modeled global sea-level contribution from Thwaites | Revised model result; assumes no additional global warming and is roughly twice earlier estimates |
| 60% chance of unpinning by 2100 | Probability that Thwaites loses its hold on the Mouginot Ridge | Model estimate, not a scheduled collapse date |
| About 0.6 meters (roughly 2 feet) | Global sea-level equivalent of all ice currently contained in Thwaites | Glacier-only total if the ice were eventually lost |
| About 4% of current global sea-level rise | Thwaites’ present contribution | Figure reported for Thwaites itself |
| About 8% of 4.5 mm per year | Contribution from the wider Amundsen Sea region | Different geographic scope from the Thwaites-only estimate |
Thwaites is approximately the size of Florida or Britain, according to the International Thwaites Glacier Collaboration. Its complete loss would add about 0.6 meters to global average sea level, but the glacier also acts as a buttress for inland ice. A larger West Antarctic Ice Sheet response could therefore produce a conditional risk of roughly 10 feet. That figure describes a possible wider response, not a forecast that all of West Antarctica will collapse on a fixed schedule.
What unpinning from the ridges could do
Two underwater ridges currently help hold back Thwaites. The new model estimates a 60% chance that the glacier will unpin from the Mouginot Ridge by the end of this century. Losing that contact could remove resistance to flow and allow retreat toward the next ridge more quickly.
Unpinning is a threshold in the glacier’s dynamics, not the same thing as instant disintegration. Ice loss would still depend on ocean conditions, bed geometry, fracture development, snowfall and feedbacks elsewhere in the ice sheet. The probability is a model output that expresses uncertainty about those processes; it is not a countdown to a guaranteed 2100 collapse.
What this means for coastal flooding
The revised result raises the amount of sea-level rise that planners may need to include from Thwaites alone. Thirty millimeters of global average rise is added to sea-level changes from Greenland, other Antarctic glaciers, thermal expansion of seawater and land-water changes. Coastal authorities therefore cannot treat the Thwaites number as a complete local-flood projection, but a higher glacier contribution narrows the margin for roads, ports, drainage systems, housing and flood defenses designed around older scenarios.
Eric Rignot of UC Irvine said the findings “predict greater risk of and exposure for coastal flooding than anticipated in the coming decades.” The relevant planning question is not whether Thwaites will suddenly add two feet of water, but whether an additional modeled contribution makes damaging high tides, storm surges and chronic flooding more likely when combined with other sources of sea-level rise.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why scientists are not declaring an imminent collapse
The 2026 result addresses a specific modeling omission: seawater intrusion through a broad, mobile grounding zone. It does not establish a precise collapse date. In December 2024, the International Thwaites Glacier Collaboration reported that a rapid catastrophic-collapse scenario this century was less likely than earlier worst-case projections, while emphasizing that the glacier remains a serious long-term risk. That assessment focused on collapse timing and system dynamics; the newer work changes how basal melting is represented. The two findings are not contradictory.
Ted Scambos, a senior research scientist at the University of Colorado Boulder who was not involved in the work, called the result “a real gamechanger for sea level forecasting from Thwaites.” Robert Larter, a marine geophysicist at the British Antarctic Survey, offered a key limitation: “The reality is that there is a lot we still need to find out about grounding zone processes to be able to make confident predictions about how fast ice will be lost.”
What happens next
Direct measurements beneath the grounding line remain scarce because the zone is remote, crevassed and covered by moving ice. The research team plans a 2028 field deployment to measure how seawater flushes through the grounding zone. Those observations should help test whether the modeled pathways, water temperatures and melt rates match conditions beneath the glacier.
Until then, the most defensible reading is that Thwaites is losing ice under a process older models underrepresented. The revised physics increases the modeled sea-level contribution and the potential exposure of coastal communities, while leaving the exact speed and ultimate scale of retreat uncertain.
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