“YOU are very aware that if something goes wrong, it goes very wrong very quickly,” says Joanne Johnson, speaking from her tent near Thwaites glacier in one of the remotest parts of Antarctica. At the time, she and three colleagues were alone, more than 1600 kilometres from the nearest research station. Strong winds had pounded them and it had snowed heavily, making the terrain even more perilous. On the bright side, it was mercifully mild, at -5°C.
Until now, fewer than 50 people have been to this part of West Antarctica, less than have been to space. By the end of this month, 100 will have visited. The reason why is simple: Thwaites is a potential climate time bomb that we need to learn much more about.
This vast glacier is about the size of Great Britain. While it has been shrinking since the early 1990s, ice loss has almost doubled over the past 20 years. It is shedding a dizzying 35 billion tonnes a year. On its own, its collapse would raise seas by around 65 centimetres. That is worrying enough in the context of the 19-cm rise in the whole of the 20th century. But the bigger worry is that this glacier buttresses the entire West Antarctic ice sheet. If Thwaites goes, the fear is it will trigger a wider collapse of ice – enough to raise seas by a calamitous 3.3 metres within a few hundred years.
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This is why it deserves its reputation as the world’s most dangerous glacier, says Sridhar Anandakrishnan at Pennsylvania State University. “What happens at Thwaites affects the whole ice sheet.”
This glacier was an enigma for a long time. It was the last part of Antarctica’s coastline to be mapped in detail, in 1940. Scientists first set foot there in the late 1950s, followed by a hiatus until research ships visited in the 1980s and 1990s. And it wasn’t until 2004 that planes with ice-penetrating radar gave us our first real idea of how thick it is, vital for knowing how it could respond to a changing climate.
Fortunately, our understanding of the glacier is set to dramatically improve. The first results are starting to trickle in from the five-year , a $50 million UK-US initiative that started in 2018. Johnson, of the British Antarctic Survey (BAS), is at the vanguard of this season’s research, which hopes to harvest data from above, below and around the glacier.
“It’s a climate time bomb. The fear is it will trigger a wider collapse of ice”
So far, most of what we know about Thwaites has been gleaned from satellites, which raised the alarm over its accelerating decline. But new observations from the field are vital if we are to more accurately answer some key questions: is the glacier’s retreat irreversible, how much will it contribute to sea level rise, and by when?
The latest update from the UN climate science panel said sea levels could rise between 26 centimetres and 1.1 metres by 2100, depending on the carbon emissions we put into the atmosphere. That is still a huge range, and the race is on to get a better idea of what will happen. We don’t even know whether the collapse of Thwaites will take decades or centuries. A clearer time frame for sea level rise is crucial for governments to plan how and when to protect low-lying coasts, such as the UK deciding when to build a new tidal barrier across the river Thames to protect London.
David Vaughan at BAS says the Thwaites project must provide the real world data to reduce the uncertainty in modelling the future. “We know the big uncertainty resides in the Antarctic and Greenland ice sheets. If we really want to predict sea level rise with some sense of clarity and usefulness, we have to nail those two things.”
To date, the difficulty of getting humans and equipment to Thwaites has meant most of our insight comes from remote monitoring. “We learned everything we know about this glacier mostly from satellite data, and some airborne data,” says Eric Rignot at the University of California, Irvine. That can reveal quite a lot. He to detect a hole at the bottom of Thwaites that would once have contained around 14 billion tonnes of ice. New work he is due to publish shows similar cavities appearing under neighbouring glaciers. The findings suggest such cavities are a common feature of Antarctica’s retreating glaciers, he says, and seem to be linked to the recent ice loss.
But to really understand the dramatic changes to Thwaites glacier, we need to get our feet wet. That’s because the end of the glacier – where its ice leaves the land and becomes a floating ice shelf – appears to be melting from below due to an influx of warmer sea water linked to climate change. At 3°C to 4°C, this water would make for a chilly swim, but such temperatures are enough to rapidly melt ice as the water sloshes in underneath the glacier. “That has a big impact, like pulling a leg out from under a stool,” says Ted Scambos of the US National Snow and Ice Data Center.
This kind of “submarine” melting seems to be exacerbated by changing ocean circulation, driven by the influx of fresh water as the glacier melts. Karen Heywood at the University of East Anglia in the UK is on a mission to shed more light on this, using animals and machines.
“The hypothesis is that the warm water is causing or enhancing the melt rate,” she says. “One of the questions is: how does that rate vary from year to year? And why?” To find out, she will be attaching tags measuring temperature and salinity to around 10 elephant and Weddell seals in coming months. Seals are handy for measuring at different water depths around the glacier because they travel from the surface to the sea bed to feed.
The other tools in her arsenal are ocean gliders. These underwater vessels, piloted remotely from the UK, were used earlier last year to unearth what Heywood says are “surprising directions of the flow beneath the glacier”, with the results due out soon. The plan is to deploy up to seven gliders in 2021 with more instruments, including devices to measure water turbulence. Microphones may also be used on them to see if anything can be learned from the noise of ice cracking.
Even some initial readings, including more accurate measurements of sea-bed depth, are proving sufficient to help build better models of Thwaites’s future, says Heywood. “There were areas which you think are going to be 500 metres deep and they’re 200 metres deep or the other way around. And that makes a huge difference to how you model.”
Drowning cities
If the West Antarctic ice sheet collapses, it will cause sea levels to rise by 3.3 metres, threatening many major cities including Hong Kong, Miami, New York, Shanghai, Osaka, Kolkata, Dhaka, Rio de Janeiro, The Hague, and London.
We also need to know much more about the properties of the bedrock that the glacier is sliding across – whether it is smooth or rough, wet or dry. “They make a huge difference in how effectively the glacier slides,” says Anandakrishnan. Right now, researchers modelling the glacier’s retreat estimate the friction of the bedrock. To replace those educated guesses with real data, Anandakrishnan and his colleagues will set off explosives and use the resulting seismic waves to and get a better idea of the friction it is exerting on the ice.
Because it would be too much work to map the entire glacier that way, the team will survey a line down its centre. That information should improve models enough for us to know whether the glacier’s retreat will unfold in this century, or over the next 1000 years. “How Thwaites responds is radically different depending on whether we think the bed is wet and sloppy or hard and dry along its length,” says Anandakrishnan.
Many of the big answers about the glacier’s future will come from looking closer at a zone known as the grounding line. This is where its ice leaves the land to form the floating ice shelf that juts into the Amundsen Sea. The line is . In one attempt to learn more, Johnson is seeking sites in this zone to drill through the ice to the bedrock. But that will be just part of a concerted effort to unravel this facet of the glacier.
“The stakes for getting a clearer picture of the future of Thwaites couldn’t be higher”
“If we are going to really understand what drives the retreat and collapse of an ice sheet, it’s all about the grounding line,” says Vaughan. That is because the glacier sits in a bowl-shaped basin of rock, getting deeper inland, with the front of the ice stabilised by sitting on the basin’s rim. If the grounding line moves back much further, certain scientists think that its position on a downward slope will prove unstable, rapidly speeding up ice loss and the line’s retreat. Some researchers say . Others think it is too early to say.
Doomsday scenarios
To find out more, scientists will soon be dodging crevasses on Thwaites to deploy drills that use hot water to tunnel down through the ice and then place sensors either side of the grounding line. The aim is to watch ice crossing the line over the next two years to see how fast the glacier’s underside is moving.
Another factor in the glacier’s fate could be the tall coastal ice cliffs that will form if the ice shelf is lost sometime in the future. Ice can only support a cliff of around 100 metres, so ice could slump off taller faces, exposing an even taller and less stable cliff behind. “You could get into a runaway situation,” says Scambos. Researchers trying to model this effect – known as marine ice cliff instability – where the West Antarctic ice sheet collapses next century an order of magnitude faster than previous estimates. But the runaway impact of ice cliffs is still just an idea – we have never seen it happen. It is by no means certain to take place either. Research led by Tamsin Edwards of King’s College London last year suggests it .
Another key avenue to better understand what will happen to Thwaites is to go back in time, to see what proxies for past climates, things such as sediment that hold a record of conditions at the time, tell us about the role warmer water has played in the glacier’s history. In October 2019, a team of scientists met in Oregon to share out cores of sediment taken earlier that year from the sea floor close to where the glacier ice meets the ocean. The aim is to find out what chemical clues are held by the fossils it contains. Previous cores taken from the Amundsen Sea at the glacier’s end led to its retreat around 10,000 years ago. Between then and last century, however, little changed – until the rapid shift began in the late 20th century. The new cores are specifically focused on Thwaites and should date back a few thousand years, helping us understand how the glacier may change in the future, hopes BAS geophysicist Rob Larter. “From the sediment cores, we’re trying to determine the history of the warm water influx onto the shelf, which everybody recognises is the main driver of the retreat.”
The goal of all this work is to help people like Helene Seroussi. Based at NASA’s Jet Propulsion Laboratory in California, she builds computer models that attempt to recreate the past changes we have seen at Thwaites in order to better project what might happen. These simulations have been improving but there is still a way to go, says Seroussi. For her, the key will be getting more observations on what is happening in the ocean, and the interaction between the ocean and the ice. Having more readings also opens up the possibility of using artificial intelligence to help predict the fate of Thwaites. But we need more data to go down that road, she says.
The stakes for getting a clearer picture of the future of Thwaites couldn’t be higher. The scientists there now should return with a treasure trove of information that will be critical for getting a better handle on sea level rise. “If we fail, and our sea level rise projections [for 2100] remain between 30 cm and a little over a metre, then that’s not a good job,” says Vaughan.
Realistically, the researchers won’t make the uncertainty disappear overnight – but it is still useful to reduce it, he says. For those managing defences on the coastlines on which a growing number of the world’s people live, it could be the early warning alarm that means cities such as New York, Shanghai and London adapt quickly enough to have a future.
Stop the flow?
Given the disastrous impact if Thwaites glacier on Antarctica vanishes, it is no wonder people are investigating ways to slow its retreat through geoengineering. In a , researchers outlined three possibilities. One idea is to extract or freeze water at the glacier’s base, to slow the sliding of ice. Others are to build a 300-metre-high island to buttress the glacier or a 100-metre-tall ridge called a berm to block the warmer water causing most of the melt.
“I don’t think it’s at all wise to begin doing any engineering on Thwaites yet,” says John Moore at Beijing Normal University, lead author of the article. The best use of resources is to investigate the glacier further, he says, which is exactly what is being done. Nevertheless, it sparked fruitful discussions in the past year with engineering groups at universities.
Anders Levermann at the Potsdam Institute for Climate Impact Research in Germany recently proposed pumping huge amounts of seawater onto the West Antarctic ice sheet, where it would freeze and stop the sheet from collapsing. He says we are still at the stage of deciding whether any geoengineering is a good idea. “We should not get into a struggle of which idea is best before society has answered the question of whether we should do something like this at all,” he says. “Everything we do down there is a major disturbance of the local ecosystem and will cost a tonne of money.”
While it is right that people discuss and evaluate potential fixes – especially given the dire consequences and huge costs of sea level rise – David Vaughan at the British Antarctic Survey says he has yet to see a proposal that isn’t “ruinously expensive to the global economy and wouldn’t produce even more carbon dioxide”.
Sridhar Anandakrishnan at Pennsylvania State University condemns talk of geoengineering fixes, too, because Antarctica is so remote and inhospitable. “It’s a non-starter.” Much easier, he says, would be action on climate change to keep the ocean from warming more.
