Photo by Derek Oyen on Unsplash
Photo by Derek Oyen on Unsplash

EXPERT REACTION: Melting of the West Antarctic Ice Sheet may now be inevitable

Embargoed until: Publicly released:
Peer-reviewed: This work was reviewed and scrutinised by relevant independent experts.

Future increases in ice-shelf melting in the West Antarctic are now potentially unavoidable, according to international experts who say this will cause sea levels to rise. The researchers looked at a computer simulation of the interactions between ice and the ocean under various emissions scenarios, and say it's likely ocean warming in the region is already locked in at about triple the historical rate. In an accompanying opinion piece, an Australian researcher agrees that some degree of sea-level rise is now locked in, but says more research is needed to confirm how much the West Antarctic Ice Sheet will contribute. Both the paper and opinion authors note the West Antarctic Ice Sheet is the largest, but not the only, contributor to sea-level rise, and other ice sheets may respond differently to climate change.

Journal/conference: Nature Climate Change

Research: Paper

Organisation/s: The University of New South Wales, British Antarctic Survey, UK

Funder: This research is part of the UKRI-JSPS project ‘Quantifying Human Influence on Ocean Melting of the West Antarctic Ice Sheet’ (NE/S011994/1, K.A.N., P.R.H.). It was also supported by the NERC LTSM project TerraFIRMA (Future Impacts, Risks and Mitigation Actions in a changing Earth system, K.A.N., P.R.H.), the EU Horizon 2020 project TiPACCs (Tipping Points in Antarctic Climate Components, 820575, J.D.R.) and a UKRI Future Leaders Fellowship (MR/W011816/1, J.D.R.). Model porting and optimization was supported by the project ‘Optimizing MITgcm on ARCHER2’ (ARCHER2-eCSE02-06, K.A.N.). Computational resources were provided by the ARCHER2 UK National Supercomputing Service.

Media release

From: Springer Nature

Climate change: Future melting of West Antarctic Ice Sheet may be unavoidable (N&V) *PRESS BRIEFING*

Future increases in ice-shelf melting in the West Antarctic over the twenty-first century may be unavoidable, a modelling study published in Nature Climate Change suggests. The findings suggest that rapid ocean warming in West Antarctica is already committed under a range of emission pathways, and mitigation efforts may only prevent the worst-case scenarios.

Ice shelves play an important role in buttressing, or slowing the flow of glaciers to the sea. The West Antarctic Ice Sheet is Antarctica’s largest contributor to sea-level rise. The ice loss is driven by interactions with the Southern Ocean, particularly in the Amundsen Sea. Data on warming in the Amundsen Sea are limited and while it has been proposed that the region will benefit from reductions in emissions, this has not been examined in detail.

Kaitlin Naughten and colleagues use a regional ocean model to understand future changes under different emissions scenarios in ocean heat and therefore ocean-driven ice-shelf melt in the Amundsen Sea, Antarctica. They find that even under a range of mitigation scenarios (including Paris Agreement 1.5 °C, Paris Agreement 2 °C and Representative Concentration Pathway (RCP) 4.5), climate change could cause the ocean to warm at three times the historical rate. They suggest this indicates that mitigation efforts may have limited power to slow ocean warming in the Amundsen Sea in the coming decades. They note that natural internal climate variability will also play a role in controlling the amount of warming caused by climate change. The authors project increased melt in areas crucial for buttressing the ice sheet and maintaining stability, with warming concentrated at an intermediate (200–700 m) depth that accesses the ice-shelf cavities, and leads to melt.

The authors acknowledge that this work is based on outputs from a single ice–ocean model. They note that mass loss from the West Antarctic Ice Sheet is just one component of sea-level rise, and other regions of Antarctica are unlikely to lose substantial mass if current emissions targets are met. Since the ice sheet will take centuries or millennia to fully respond to climate change, the choice of emissions scenario could have a larger impact farther in the future, beyond the 21st century, the authors conclude.

In an accompanying News & Views article, Taimoor Sohail writes, “This study by Naughten et al. represents the most comprehensive set of future projections of warming in the Amundsen Sea so far. While the window to prevent ice-shelf melting in the West Antarctic is likely to have passed, the true impacts of climate change on sea level will depend on a variety of factors.”

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Expert Reaction

These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.

Dr Tom Mortlock is Head of Climate Analytics Asia-Pacific at Aon, and Adjunct Fellow in the Climate Change Research Centre at UNSW

Sea level rise is one of the clearest signals of a warming world, and irrespective of whether we reach net zero greenhouse gas emissions tomorrow, we will continue to see global sea levels rise up to and beyond 2100. The impact of sea level rise on the coast is not just a slow increase of water lapping at the shore – it increases the frequency of coastal flooding events when storms occur. Coastal engineers use the rule of thumb that every 10cm of sea level rise increases the frequency of a given coastal flood by a factor of three.

Most of our coastal infrastructure has sea level rise allowances built into the design. However, these will typically include median estimates of sea level rise provided by the IPCC, not much more that 1 m by 2100. Extreme rates of sea level rise - triggered by tipping points such as the collapse of the West Antarctic Ice Sheet - are extremely difficult to incorporate into coastal risk management. This is because projections remain highly uncertain, and we have little idea of the probability and timing of this occurring. 

This new research suggests that accelerated melting of the West Antarctic Ice Sheet is now locked in, even for the most ambitious emissions reduction targets. While the research was undertaken using only a single model and forcing field, it highlights the urgency with which we need to better understand these high-magnitude sea level rise scenarios in order to incorporate them into risk-based coastal management.

Last updated: 23 Oct 2023 11:13am
Declared conflicts of interest:
None declared.
Professor Matt King is Director of the Australian Centre for Excellence in Antarctic Science, and Professor of Geography & Spatial Sciences at The University of Tasmania

The ocean is the greatest enemy of Antarctic ice. 

This new study is sobering reading because it suggests that we have passed the point of no return when it comes to ocean melting of one key area of West Antarctica. 

The Amundsen Sea Embayment is the hotspot for current melting of the ice sheet on land – driving up sea levels. This study suggests that the glaciers in this region are destined for increased melt through the rest of this century. If the work is correct, that means that some sea-level rise and coastal flooding along our beloved coastlines is locked in even if we take very strong action on climate change. 

But the authors suggest we should not give up hope despite the bad news in their paper – they note that much of the wider Antarctic Ice Sheet can be saved with strong climate action, and with it many metres of avoided sea-level rise. But I would not rule out the West Antarctic Ice Sheet being saved by rapid climate action despite this study, since even cutting edge studies like this can’t yet consider all the processes that may be important to the future of the ice sheet. 

Hundreds of $B of Australian infrastructure and tens of thousands of homes are vulnerable to even 1m of sea level rise, and that is at play this century. Many of our regional neighbours are even more exposed -  Australia claims 42% of Antarctica and the nations are looking to us to provide the knowledge. 

If we’re all going to adapt to rising sea levels in a sensible way we have to be able to say more confidently how much and how fast. That will require new knowledge of how Antarctica works that can be rapidly turned into more confident predictions of the future of sea levels.

Last updated: 23 Oct 2023 11:13am
Declared conflicts of interest:
None declared.
Matthew England is Scientia Professor of Ocean & Climate Processes at the University of New South Wales Centre for Marine Science and Innovation, and Deputy Director of the ARC Australian Centre for Excellence in Antarctic Science.

This is a confronting paper to read. The authors find that our emissions to date have already locked in strong warming at the ice shelf margin around West Antarctic sector. The authors use a high-resolution ocean circulation model to infer that West Antarctica is set for several measures of sea level rise over the coming centuries. Alongside thermal expansion and melting of Greenland, costly adaptation measures will be needed for our coastal cities and infrastructure; worldwide.

Last updated: 23 Oct 2023 11:13am
Declared conflicts of interest:
None declared.
Dr Ariaan Purich is a Research Fellow in the ARC Special Research Initiative Securing Antarctica's Environmental Future at Monash University

This year we’ve been hearing a lot about Antarctica - meltwater is slowing down the deep ocean circulation and sea ice coverage has been exceptionally low. Now, Kaitlin Naughten and colleagues provide modelling evidence suggesting that future melting of ice shelves in the Amundsen Sea is locked in due to ocean warming - even under ambitious mitigation scenarios, committed ocean warming will increase ice shelf melting in this region. This will have dire consequences for the stability of the West Antarctic Ice Sheet and global sea level rise. 

These new findings are alarming. It's important to note that the study by Naughten et al. is based on a single ocean-ice model that does not represent all feedbacks - to better understand these future drastic changes, more research is needed. 

In the face of such concerning news, we also need to remember that while melting of West Antarctica may be unavoidable, this is not the case for other crucial climate tipping points, such as East Antarctica. We urgently need to reduce our greenhouse gas emissions to limit future change - there is still hope if we act now.

Last updated: 23 Oct 2023 11:12am
Declared conflicts of interest:
None declared.
Dr Edward Doddridge is a Physical Oceanographer with the Australian Antarctic Program Partnership at the Institute for Marine and Antarctic Studies, University of Tasmania

The Amundsen Sea region considered in this paper is a bellwether for change in the Antarctic region. In recent decades the ocean has warmed and the ice shelves have retreated. In late 2022, sea ice melted earlier than normal, leading to the death of approximately 10,000 Emperor Penguin chicks in the nearby Bellingshausen Sea. After record summer lows, the sea ice returned many months later than normal.

The new results in this paper suggest that the huge changes we've seen in the Amundsen Sea region are unlikely to be aberrations - they are glimpses into a future that we can no longer avoid.

It is confronting to think that five metres of sea level rise is already locked in. But, we should not see this result as a reason to despair, rather as an urgent call to action. Yes, climate change will negatively impact the future, but through our actions right now we can choose how bad it gets.

Last updated: 23 Oct 2023 11:12am
Declared conflicts of interest:
In 2020 Kaitlin Naughten and Edward were co-authors on an unsuccessful grant application led by a colleague.
Dr Jordan Pitt is Associate Dean of Indigenous Strategy and Services (Science) at The University of Sydney

This paper continues the major trend I have seen over my lifetime. The continued worsening of observations and model predictions of the climate which are at odds with the continued unwillingness to set and achieve meaningful action to reduce emissions.

This is a trend that diminishes our power to make effective change over time, as the longer we go with ineffectual changes, the more unprecedented the changes become and the more difficult it is to reverse course. 

Indeed the paper demonstrates that we may already be in this position for the melting of the West Antarctic Ice Shelf over this century. 

While more models and the incorporation of other physical processes can help resolve exact details, the overall picture remains bleak. 

The effect of continued emissions on the climate is complex but its source is not.

Last updated: 23 Oct 2023 11:11am
Declared conflicts of interest:
None declared.

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