Dr. Chen Zhao on Antarctica’s Subglacial Melt – A Sea Level Rise Driver We’ve Missed

By Chen Zhao 23 September, 2025

Glaciologist Dr. Zhao on the hidden threat beneath Antarctica that could drastically accelerate sea level rise

Subglacial meltwater is a hidden driver of rapid ice loss that is not included in most sea-level rise projections; include this could triple ice flow & add >2m to sea levels by 2300
The interaction of subglacial meltwater with ice dynamics suggests that tipping points for ice sheet collapse could be reached sooner than currently projected possibly by 2050
This profound uncertainty means we risk being blindsided by rapid, irreversible collapse, demanding urgent improvements to predictive models of sea level rise
Author: Chen Zhao
Dr. Chen Zhao is a glaciologist, and an ice sheet modeler affiliated with the Institute for Marine and Antarctic Studies, University of Tasmania (UTAS). She is interested in exploring the sea-level contributions from the Antarctic Ice Sheet in a changing climate and assessing the impact of climate systems on large ice sheets with numerical modelling. she has experience of managing successful collaborative research projects, producing major outputs including papers in Nature and Nature Comm. She has secured $2.4 million in research funding and $2.12 million in-kind support from the National Computing Merit Allocation Scheme. She led the only Australian group to participate in the Ice Sheet Model Intercomparison Project (ISMIP6), contributing to the sea-level rise projections in the IPCC AR6 report, for which she received the Richardson Medal by the International Glaciological Society as part of the ISMIP6 team. Dr. Zhao is deeply passionate about elucidating the connection between the Antarctic ice sheet and sea-level rise, and its implications for future generations. She represented early career scientists in the Cryosphere Pavilion at COP27 in Egypt to elevate scientists' voices on the significant changes occurring in the cryosphere to governments, non-profits, and the media.
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Antarctica is melting rapidly as temperatures in the South Pole reach new heights. This poses a great risk to coastal cities around the world – the complete collapse of the West Antarctic Ice Sheet would unleash 3-5m of additional sea level rise. Yet it’s very challenging to predict exactly how ice sheets will behave in the future because there are many factors at play.

Today we ask glaciologist and ice sheet modeler Dr. Chen Zhao about a “hidden threat” to ice loss – subglacial water. If included in ice sheet models, she finds it may triple ice loss and add more than 2m to global sea levels by 2300.

CWR: Your latest Nature Communications article showed how “hidden” subglacial meltwater beneath Antarctica’s ice can accelerate ice loss. What is “subglacial meltwater”? Why did we not account for it? And why does it lead to faster ice loss?

Dr. Chen Zhao (CZ): Subglacial meltwater refers to water that forms beneath grounded ice sheets and glaciers, primarily due to friction from the movement of the ice or geothermal heat from the bedrock below.

Subglacial meltwater is “hidden” under >2km of ice

We haven’t fully accounted for it because, first, this water is largely hidden – buried under more than two kilometres of ice – making it extremely difficult to observe. Second, we still lack a complete understanding of how subglacial water systems evolve over time and how they influence ice flow across different regions. As a result, some ice-sheet models either neglect its role or apply oversimplified assumptions.

It acts like a lubricant that slides ice more rapidly toward the ocean = faster ice loss…

This meltwater can act like a lubricant at the ice-bed interface, reducing friction and allowing the ice to slide more rapidly toward the ocean. Additionally, although not the focus of our recent paper, subglacial meltwater that discharges into ice shelf cavities can enhance basal melting beneath ice shelves. This reduces their buttressing effect on inland ice and can further accelerate ice mass loss.

CWR: Does this mean that existing sea-level rise projections are too low as they do not fully account for this hidden meltwater?

Dr. CZ: Possibly. Many existing sea-level rise projections either neglect subglacial meltwater or use oversimplified assumptions, which could lead to underestimates of Antarctic ice loss. However, it’s important to recognise that projections also contain other major uncertainties – such as future snowfall and surface melt – that may push estimates in either direction.

…it can triple the amount of ice flowing to the ocean, adding >2m of SLR by 2030

Our study highlights that subglacial hydrology is a key missing piece. Including it in ice sheet models is crucial to improving the accuracy of future sea-level rise projections. Our results show that doing so can triple the amount of ice flowing to the ocean, potentially adding more than two metres to global sea levels by 2300, with potentially enormous consequences for millions of coastal communities worldwide, including economic damage reaching trillions of dollars, damaged vital infrastructure and reshaped coastlines worldwide.

CWR: Would this mean that we’ll also have to revise the expected timing of tipping points? Would we cross these irreversible thresholds earlier? What does this mean?

Dr. CZ: It might. The interaction between subglacial meltwater and ice dynamics could mean that tipping points – irreversible thresholds of ice sheet collapse – occur sooner than expected. This would significantly shorten the time we have to take meaningful action to avoid long-term, irreversible changes. Our study indicates that most regions will cross this threshold earlier, with some potentially doing so by 2050. This is deeply concerning.

Most regions will cross this threshold earlier, some potentially by 2050

CWR: These findings are clearly important as they indicate that we could see rapid, irreversible ice loss and sea level rise sooner than we think. What keeps you up at night and what research should be prioritised?

Dr. CZ: What concerns me most is the deep uncertainty surrounding Antarctica’s future – and how that translates into uncertainty in sea-level rise. We are discovering that processes we once thought were slow are actually shockingly fast, and this deep uncertainty means we could be blindsided by rapid, irreversible ice loss. To reduce this, we need to prioritise:

  1. Coupled ice-hydrology-ocean models that capture key interactions
  2. Improved model initialisation to reflect the current state of the ice sheet
  3. Better constraints on surface mass balance
  4. More accurate representation of processes like iceberg calving

These efforts are essential to improve the reliability of sea-level rise projections.

CWR: Are there any other “hidden” ice risks we should be worrying about?

Dr. CZ: Absolutely. Basal sliding is another major unknown, especially in East Antarctica. We lack detailed knowledge of bedrock conditions – such as roughness and whether the bed is hard or soft – which strongly influence how sensitive the ice is to subglacial water.

The sliding laws we use rely on parameters we can’t currently observe, so we’re forced to make assumptions. This adds to the uncertainty.

CWR: The evidence is clear that only rapid decarbonisation will preserve the world’s glaciers and prevent climate tipping points, yet global action is stalling. What would be your message to policy makers at the upcoming COP29?

Dr. CZ: Subglacial meltwater is just one of several overlooked factors that could cause us to underestimate Antarctica’s contribution to sea-level rise. The window for action is closing faster than expected. We must remember: the melting point of ice is not negotiable.

CWR: As an ice sheet modeller, you are seeing the alarming rate of ice loss first-hand. Do you experience climate anxiety? If so, how do you manage it?

Dr. CZ: Yes – especially when I think about my children’s future. It’s heartbreaking to imagine the climate challenges they might face due to choices made today. But I try to stay hopeful. We must believe that change is still possible. If I gave up now, I’d be giving up on their future too.

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