Water beneath Antarctica’s ice can change how quickly glaciers slide toward the ocean, potentially increasing ice loss and sea-level rise. A 2025 computer model found a much larger Antarctic contribution when it included subglacial water, but that result is conditional: scientists still lack observations of how water pressure is distributed beneath the ice sheet. A separate threat—warm ocean water melting floating ice shelves—acts in a different place and should not be confused with water under the grounded ice.
What is happening beneath Antarctica’s ice?
The Antarctic Ice Sheet rests on bedrock, and parts of its base are wet. Heat from friction as ice moves and geothermal heat from below can melt ice at the bed, producing water. That water may drain through a spread-out network beneath the ice or become concentrated in channels, as described in a 2025 study by Chen Zhao and coauthors in Nature Communications.
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Water at the ice-bed interface affects the pressure pressing ice against the bed. That pressure helps determine friction and therefore basal sliding: how readily the ice moves over the ground. If sliding speeds up, more grounded ice can flow toward the coast and enter the ocean. The water does not simply melt the entire ice sheet from below; its potential influence is through the way it changes the motion of grounded ice.
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Researchers do not yet know the actual distribution of effective pressure—the pressure that governs contact and friction between the ice and its bed—beneath the Antarctic Ice Sheet. Zhao and coauthors identify this as a major observational and modeling uncertainty. Basal sliding is consequently difficult to constrain, and the response can differ from one basin to another.
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That uncertainty matters because projections of future ice loss depend partly on how the model represents water pressure and sliding. A modeled response is not a direct measurement of current water conditions or a certain forecast of future sea-level rise.
What did the 2025 subglacial-water model find?
Zhao and coauthors used the Elmer/Ice Antarctic Ice Sheet model to examine basal-water assumptions over 2015–2300. In their model experiments, incorporating subglacial water amplified ice discharge by up to threefold and could add 2.2 metres to sea-level rise by 2300. These are outcomes of that model and its assumptions, not observed contributions or a prediction that Antarctica will necessarily produce that much rise.
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The study’s central significance is that omitting water beneath the ice could miss an important influence on ice movement. Its headline values show how consequential that model choice can be; they do not establish the future response of every Antarctic basin.
Is warm ocean water melting Antarctic ice shelves?
Yes, but this is a separate process from subglacial water. Ice shelves are floating extensions of grounded glaciers. Ocean water circulates beneath them and can melt their undersides. As a shelf thins or retreats, it can provide less buttressing—the restraining effect that slows the grounded ice behind it. Reduced buttressing can allow more land-based ice to flow into the ocean.
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A 2024 study by Emily A. Hill, G. Hilmar Gudmundsson and David M. Chandler in Nature Climate Change modeled a possible shift to a warmer ocean state in the cavities beneath the Filchner–Ronne and Ross ice shelves, which are currently colder. In those warm-state simulations, cavity temperatures rose by 2 to 4 °C and sub-shelf melt rates increased by approximately an order of magnitude. Applying those modeled melt rates to a present-day ice-sheet configuration led to increased ice loss and irreversible grounding-line retreat in some simulations.
The authors did not report an observed shift already occurring beneath these shelves. They found no indication that the Filchner–Ronne and Ross catchments—which are not currently contributing significant sea-level rise—would change that status in the near future under current climate conditions. The modeled danger depends on a change to a warm ocean state.
How the two Antarctic risks differ
| Question | Subglacial water | Warm water beneath ice shelves |
|---|---|---|
| Where is the water? | At the interface between grounded ice and bedrock. | In ocean cavities beneath floating ice shelves. |
| How could it affect sea level? | By changing basal pressure and friction, which can alter how quickly grounded ice slides toward the ocean. | By thinning shelves and reducing their buttressing of grounded ice, allowing more ice to flow seaward. |
| What does the cited evidence establish? | A 2025 ice-sheet model found a potentially large effect, while the actual distribution of basal effective pressure remains unknown. | A 2024 modeling study tested consequences of a possible warm-cavity regime shift; it did not establish that such a shift is currently underway. |
| What is the key qualification? | Results depend on model assumptions about basal water pressure and sliding; responses vary by basin. | The timing varies among ocean-model forcings, and the simulations simplify some processes. |
What should readers take from the sea-level numbers?
The 2.2-metre figure belongs to the 2025 subglacial-water model and its assumptions through 2300. The 2024 study’s temperature and melt-rate figures describe warm-state cavity simulations, not a continent-wide sea-level estimate. The two studies examine different mechanisms and scenarios; their numbers cannot be added together or treated as one forecast.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsHill, Gudmundsson and Chandler note that coupled ice–ocean modeling is needed to narrow the response timescales for the shelf-cavity scenarios. For the subglacial-water question, better constraints on basal pressure are central to reducing uncertainty. Neither study supplies a single deterministic timeline for Antarctic ice loss.
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