meltwater under the ice sheet amplifies sea-level rise
- Written by: Chen Zhao, ARC DECRA Senior Research Fellow, Institute for Marine and Antarctic Studies, University of Tasmania
One of the biggest challenges in predicting Antarctica’s deeply uncertain future is understanding exactly what’s driving its ice loss.
A vast network of lakes and streams lies beneath the thick ice sheet. This water can lubricate the ice, allowing it to slide more rapidly toward the ocean.
Our new research shows “subglacial water” plays a far larger role in Antarctic ice loss than previously thought. If it’s not properly accounted for, future sea-level rise may be vastly underestimated.
Including the effects of evolving subglacial water in ice sheet models can triple the amount of ice flowing to the ocean. This adds more than two metres to global sea levels by 2300, with potentially enormous consequences for coastal communities worldwide.
How hidden lakes threaten Antarctic Ice Sheet stability. (European Space Agency)Understanding the role of subglacial water
Subglacial water forms when the base of the ice sheet melts. This occurs either due to friction from the movement of the ice, or geothermal heat from the bedrock below.
The presence of subglacial water enables ice to slide over the bedrock more easily. It can also cause further melting under ice shelves, leading to even faster ice loss.
So it’s crucial to understand how much subglacial water is generated and where it goes, as well as its effect on ice flow and further melting.
But subglacial water is largely invisible. Being hidden underneath an ice sheet more than two kilometres deep makes it incredibly difficult to observe.
Scientists can drill boreholes through hundreds to thousands of metres of ice to get to it. But that’s an expensive and logistically challenging process.
Alternatively, they can use ice-penetrating radar to “see” through the ice. Another technique called laser altimetry examines changes in the height of the ice at the surface. Bulges might appear when lakes under the ice sheet fill, or disappear when they empty.
More than 140 active subglacial lakes have been identified beneath Antarctica over the past two decades. These discoveries provide valuable insights. But vast regions — especially in East Antarctica — remain unexplored. Little is known about the connections between these lakes.
What we did and what we found
We used computer simulations to predict the influence of subglacial water on ice sheet behaviour.
We used two computer models:
Then we explored how different assumptions about subglacial water pressure affect ice sheet dynamics. Specifically, we compared scenarios where water pressure was allowed to change over time against scenarios where it remained constant.
When the effects of changing subglacial water pressure were included in the model, the amount of ice flowing into the ocean under future climate nearly tripled.
These findings suggest many existing sea-level rise projections may be too low, because they do not fully account for the dynamic influence of subglacial water.
Our research highlights the urgent need to incorporate subglacial water dynamics into these models. Otherwise we risk significantly underestimating the rate and magnitude of future sea-level rise.
In the video below, the moving dark lines show where grounded ice begins to float. The left panel is a scenario where subglacial water is not included in the ice sheet model and the right panel is a scenario that includes the effects of evolving subglacial water.
Simulated Antarctic ice velocity over 1995–2300, using the Elmer/Ice model of ice sheets.A looming threat
Failing to account for subglacial water means global sea-level rise projections are underestimated by up to two metres by 2300.
A two-metre rise would put many coastal cities in extreme danger and potentially displace millions of people. The economic damage could reach trillions of dollars, damaging vital infrastructure and reshaping coastlines worldwide.
It also means the timing of future tipping points are underestimated too. This is the point at which the ice sheet mass loss becomes much more rapid and likely irreversible. In our study, most regions cross this threshold much earlier, some as soon as 2050. This is deeply concerning.
A chart contrasting the different contributions to sea-level rise from the Antarctic Ice Sheet depending on how subglacial water pressure is included.
Zhao, C., et al, 2025. Nature Communications.
The way forward
Understanding Antarctica’s hidden water system is challenging. The potential for rapid, catastrophic and irreversible ice loss remains.
More observations are needed to improve our models, particularly from remote regions such as East Antarctica. Continuing to gather information from boreholes, ice-penetrating radar and satellites will help us better understand how the underside of the ice sheet behaves. These techniques can then be combined with computer simulations to enable more accurate projections of future ice loss and sea-level rise.
Our new research shows integrating subglacial water dynamics into ice sheet models is a top priority. Understanding this hidden threat is crucial as the world grapples with the consequences of global warming especially rising seas.
Authors: Chen Zhao, ARC DECRA Senior Research Fellow, Institute for Marine and Antarctic Studies, University of Tasmania
