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What the survey is trying to find out
The survey targets a specific question: when a floating ice shelf retreats, can the newly exposed, tall ice front fail again and again, releasing grounded inland ice quickly enough to accelerate global sea-level rise? Its proposed answer would come from a continent-wide record of Antarctic marine cliffs assembled with remote sensing over many decades. The description appears in a 2024 Scientific Committee on Antarctic Research (SCAR) conference abstract; a final continent-wide dataset and statistical results were not yet available in the public record.
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That distinction matters. The survey is intended to test an observational stability limit for cliffs. It does not calculate how many metres of sea-level rise will occur, and it does not establish that a collapse will happen. Its value is that repeated measurements across different ice, ocean and climate settings could show whether real cliffs remain stable, calve episodically or enter a self-reinforcing failure pattern.
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Marine ice-cliff instability is a hypothesis about what can happen after ice-shelf loss. Ice shelves are floating extensions of glaciers. Their contact with side walls, islands and the seabed provides buttressing that slows the flow of grounded ice toward the ocean. If a shelf thins or retreats, the grounded ice behind it can flow faster and expose a higher vertical face at the coast.
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MICI proposes that a sufficiently tall, unsupported cliff cannot carry its own weight. A failure would remove the front section, expose another tall face and potentially repeat the process. Faster inland discharge would add more water to the ocean than ordinary shelf retreat alone. Earlier high-end scenarios that included this mechanism produced roughly twice the 2100 global mean sea-level rise of other projections, which is why the hypothesis has attracted intense scrutiny.
Why a height threshold is not the whole problem
Cliff height is only one control on failure. The 2024 Annual Review of Earth and Planetary Sciences identifies long-term internal glaciological stress as the primary driver of calving, while noting that thinning can make an ice front more vulnerable to environmental forcing. Whether a cliff fails also depends on pre-existing cracks, the geometry and connectivity of fracture networks, stress concentrations, the style and frequency of calving, and how quickly the remaining ice flows and thins.
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Those feedbacks make the theory disputed rather than settled. A cliff can lose height through calving without triggering a runaway sequence, while rapid flow may reduce the height and stress of the next exposed face. The review’s authors argue that such theories must be tested across a wide range of modern and paleo-ice-sheet conditions, not only in one modeled setting.
What scientists have observed—and what remains hypothetical
| Evidence or experiment | What it represents | What it can establish |
|---|---|---|
| Planned SCAR 2024 remote-sensing survey | Observed cliff geometry and change across Antarctica over multiple decades | Whether real marine cliffs show a repeatable stability limit or failure behavior |
| 2024 three-model MICI assessment | Parameterized simulations of severe West Antarctic shelf loss and grounding-line retreat | How the tested model formulation responds under specified hypothetical conditions |
| IPCC AR6 projections | Scenario-based global sea-level ranges with and without low-confidence MICI | The size of the uncertainty envelope, not the probability that a collapse will occur |
The survey description does not report a completed observational result. Claims that Antarctic cliffs have already demonstrated or disproved a continent-wide collapse threshold would therefore go beyond the available evidence. The observations are meant to test the premise on which a model parameterization rests; they are not a substitute for a dynamical ice-sheet simulation.
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What the newest modeling found
A Nature Climate Change summary of work led by Mathieu Morlighem describes a revised MICI parameterization run in three ice-sheet models. In experiments that removed currently stabilizing ice shelves in the Amundsen Sea Embayment, the cliffs did not collapse. The models also imposed grounding-line retreat that exposed much higher cliffs, yet still did not produce runaway failure.
In those experiments, greater ice discharge was offset by faster flow and thinning. Those responses reduced the height or stress of the exposed front quickly enough to stabilize the system under the tested formulation. The open Science Advances record likewise reports no 21st-century MICI vulnerability for the West Antarctic Ice Sheet with that parameterization.
What that result does—and does not—say
- It says the modeled West Antarctic cliffs did not enter a runaway MICI sequence in the severe experiments that were run.
- It does not show that ice shelves are safe from rapid melting, grounding-line retreat or ordinary dynamic ice loss.
- It does not prove every possible fracture law, calving rule or stress treatment will produce the same result.
- It does not eliminate high-end sea-level outcomes on longer time scales, where uncertainties in ice dynamics remain substantial.
The authors’ interpretation is therefore narrower than “the doomsday scenario is disproved”: West Antarctica remains at high risk of rapid melt, but may not be vulnerable to MICI in the near future under the tested physics.
How much sea-level rise depends on MICI?
The IPCC Sixth Assessment Report separates processes that can be projected with at least medium confidence from the low-confidence contribution of MICI. For global mean sea level in 2150, the likely range is 0.6 metres (0.4–0.9 m) under SSP1-1.9 and 1.4 m (1.0–1.9 m) under SSP5-8.5 for the processes that meet that confidence threshold.
For 2300, the IPCC gives 0.3–3.1 m under SSP1-2.6 and 1.7–6.8 m under SSP5-8.5 without MICI. Including low-confidence MICI raises the SSP5-8.5 outcome to as much as 16 m. These are scenario outcomes, not a forecast that cliffs will collapse. The large difference shows why an observational test matters most for the upper tail of long-term projections, especially under sustained high emissions.
| Horizon and scenario | Processes projected with at least medium confidence | Effect of including low-confidence MICI |
|---|---|---|
| 2150, SSP1-1.9 | 0.6 m likely (0.4–0.9 m) | Not stated by IPCC in the cited figures |
| 2150, SSP5-8.5 | 1.4 m likely (1.0–1.9 m) | Not stated by IPCC in the cited figures |
| 2300, SSP1-2.6 | 0.3–3.1 m | Not stated by IPCC in the cited figures |
| 2300, SSP5-8.5 | 1.7–6.8 m | Up to 16 m when low-confidence MICI is included |
Even if future observations make MICI unlikely, those ranges still include serious risks from ocean-driven melting, shelf weakening, grounding-line retreat, ice-sheet thinning and faster discharge. Removing one mechanism from the upper tail is not the same as removing Antarctic sea-level risk.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why observations and models can disagree
Remote sensing and modeling answer related but different questions. An observational series records what cliffs actually did under the climate and ocean conditions that occurred. A model must represent fracture, calving, stress redistribution, ice flow and thinning with equations or parameterizations, then explore conditions that have not yet occurred—such as simultaneous shelf removal and extreme grounding-line retreat.
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What to watch for as the survey develops
- A released multidecadal dataset: Look for the geographic coverage, time span, measurement uncertainty and criteria used to define a collapse or stable calving.
- Tests across ice settings: A result should be checked across different shelf geometries, bed conditions, flow speeds and fracture patterns rather than inferred from one embayment.
- Connection to model physics: The useful outcome is not merely a catalog of cliff heights, but evidence that can validate or reject the stability rules used in ice-sheet models.
- Time-scale language: “No 21st-century MICI” is a statement about a modeled horizon, not a guarantee for 2150 or 2300.
- Separate drivers: Reports should distinguish cliff failure from ocean warming, shelf thinning, grounding-line retreat and ordinary acceleration of grounded ice.
The most defensible conclusion today is that MICI remains a live, contested hypothesis being tested against observations and revised modeling. The latest three-model assessment weakens the case for a near-term runaway cliff collapse in West Antarctica under its parameterization, while the planned survey could determine whether that stability is consistent with Antarctic cliffs over many decades. Until the observations and broader model tests are available, the prudent interpretation is lower confidence in the most extreme MICI-driven outcomes—not a reprieve from rapid Antarctic ice loss or rising seas.
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