# Thwaites Glacier Model With Melting "Grounding Zones" Projects Up to 30mm Sea Rise by 2100 URL: https://edufabtech.com/news/thwaites-glacier-grounding-zone-model-sea-level-2100 Section: News · Climate & Energy Published: 2026-10-22 Publisher: EduFabTech (https://edufabtech.com) > A study published in Nature Communications on 12 October 2026 finds Thwaites Glacier could contribute up to 30 ± 6mm of global sea-level rise by 2100, about double the mean ISMIP6 ensemble estimate. A study published in *Nature Communications* on 12 October 2026 finds that Thwaites Glacier, one of the fastest-changing outlets of the West Antarctic Ice Sheet, could contribute up to 30 ± 6mm of global mean sea-level rise by 2100 under a model that treats the area where the glacier meets bedrock as a widening "grounding zone" rather than a fixed line. The work, led by Mattia Poinelli together with Eric Rignot, Hélène Seroussi, Joshua Cuzzone, Tyler Pelle and Eric Larour, was announced by NASA's Jet Propulsion Laboratory on 20 October 2026, which worked on the model together with the University of California, Irvine, and Dartmouth College. ## Why the grounding line was the wrong boundary Ice-sheet models have long treated the "grounding line" — the point where a glacier stops resting on bedrock and starts floating on the ocean — as a single, sharp boundary. The Nature Communications paper argues that under Thwaites, seawater intrudes several kilometres beneath the grounded ice, lifting it during tidal cycles and melting it from below across a zone rather than a line. The authors calibrated an ice-sheet model (ISSM) against satellite observations of Thwaites Glacier's retreat, thinning and acceleration from 1996 to 2023, and found it could only reproduce that 27-year record when the grounding zone was represented as actively melting across a 2–5km-wide band. ![A bar chart shows modeled sea-level contribution from Thwaites Glacier rising from 8.3mm to 30.1mm as the assumed grounding-zone width grows from a fixed line to 5±1km, compared against the ISMIP6 ensemble mean of 15.2mm.](https://edufabtech.com/uploads/2026/10/thwaites-glacier-grounding-zone-model-sea-level-2100-2.png) *A bar chart shows modeled sea-level contribution from Thwaites Glacier rising from 8.3mm to 30.1mm as the assumed grounding-zone width grows from a fixed line to 5±1km, compared against the ISMIP6 ensemble mean of 15.2mm. — EduFabTech · Own work* ## What the range of numbers shows The projected sea-level contribution by 2100 scales directly with how wide the modeled grounding zone is, and the paper reports a range rather than a single figure: - No grounding zone (line only): 8.3 ± 3.0mm - 1 ± 1km grounding zone: 14.3 ± 3.1mm - 3 ± 1km grounding zone: 19.4 ± 5.2mm - 5 ± 1km grounding zone: 30.1 ± 5.7mm The authors compare their widest-zone, best-fitting scenario to the mean projection from the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6), an ensemble of glacier models used in international climate assessments, which put Thwaites' contribution at 15.2 ± 21.8mm by 2100. The new estimate is described in the paper as roughly double that ISMIP6 mean. Because the result scales with assumed grounding-zone width, the authors present it as a range tied to that width rather than a single number. ## A possible tipping point at Mouginot Ridge Beyond the raw volume of ice loss, the model identifies a specific structural risk: a 60% probability, under the 5 ± 1km grounding-zone scenario — the same widest, best-fitting scenario used for the 30mm estimate — that Thwaites unpins from an underwater feature the authors call the Mouginot Ridge before 2100, a stabilizing pinning point that currently helps slow the glacier's retreat. Under that widest grounding-zone scenario, the paper's simulations show this unpinning could occur as early as 2038. For the narrower 2–3km grounding-zone scenarios, the modeled probability of unpinning by century's end drops to around 45%. ## What the model leaves out The authors are explicit about the simplifications built into the model. The simulations hold the ice front fixed throughout, meaning they do not account for calving of icebergs. Ocean melting beneath the ice is represented with a simplified parameterization rather than a fully coupled ocean-circulation model, and the grounding-zone width itself is held fixed in each scenario rather than allowed to vary with local seafloor conditions, which the paper notes is a simplification of what is likely a spatially variable process. The paper also estimates that future ocean warming could raise basal melt rates by roughly 10 metres per year, which would increase the sea-level projections by around 15% on top of the ranges above. ![A three-tier risk ladder shows the modeled probability of Thwaites unpinning from the stabilizing Mouginot Ridge before 2100, rising from unmodeled in a line-only approach to ~45% at a 2–3km zone to a critical ~60% — possibly as early as 2038 — at the widest 5km zone.](https://edufabtech.com/uploads/2026/10/thwaites-glacier-grounding-zone-model-sea-level-2100-3.png) *A three-tier risk ladder shows the modeled probability of Thwaites unpinning from the stabilizing Mouginot Ridge before 2100, rising from unmodeled in a line-only approach to ~45% at a 2–3km zone to a critical ~60% — possibly as early as 2038 — at the widest 5km zone. — EduFabTech · Own work* ## Why the method matters more than the headline number For students and researchers working in glaciology, oceanography or climate modeling, the significant result is arguably methodological rather than the 30mm figure itself: a model that explicitly represents an actively melting grounding zone reproduced three decades of satellite-observed retreat, thinning and acceleration far better than models that treat the grounding line as a single boundary — matching the historical record, according to NASA/JPL's announcement, about four times more closely. That gives ice-sheet modelers a mechanism — tidally driven seawater intrusion beneath grounded ice — to test against other Antarctic outlet glaciers with similar bed geometry, rather than only against Thwaites. The paper itself frames its central estimate as a maximum under specific assumptions, not a forecast: the 30mm figure corresponds to the widest grounding-zone scenario the authors tested and calibrated against observations, while narrower zones produce smaller contributions, as low as roughly a quarter of that figure with no grounding zone at all. Readers comparing this result to the ISMIP6 ensemble, or to other Antarctic sea-level studies, should carry the grounding-zone width and its uncertainty range along with any single number drawn from this paper. ## Sources 1. Mattia Poinelli, Eric Rignot, Hélène Seroussi, Joshua Cuzzone, Tyler Pelle, Eric Larour. (2026). Sea-level contribution from Thwaites Glacier doubles in an observation-constrained ice-sheet model. Nature Communications https://doi.org/10.1038/s41467-026-77976-1 2. NASA Jet Propulsion Laboratory. (2026). NASA Study Refines Projections for Thwaites Glacier. NASA/JPL https://www.jpl.nasa.gov/news/nasa-study-refines-projections-for-thwaites-glacier/ --- Source page: https://edufabtech.com/news/thwaites-glacier-grounding-zone-model-sea-level-2100 Quote with a link to the source page. © EduFabTech.