The fates of coastal cities worldwide, from New York to Manila, depend on a vast but little-understood Antarctic glacier that is losing ice alarmingly quickly.
Now, extensive research efforts in the world鈥檚 least-hospitable environment are revealing why Thwaites glacier 鈥� dubbed the doomsday glacier 鈥� is so dangerous, and whether its demise can be avoided.
鈥泪 think 鈥榓we鈥� is the best word for being there.鈥� This is how at the University of Houston in Texas describes what it is like to be one of the few people to have visited Thwaites glacier, one of the hardest-to-reach places on Earth.
This vast mass of ice is 1 kilometre thick and comparable in size to Great Britain or Florida. At the point where it meets the ocean, Thwaites is 120 km wide, making it the world鈥檚 widest glacier. 鈥泪t is essentially an enormous, slow-moving river of ice that flows off the continent,鈥� says at the British Antarctic Survey (BAS). 鈥淭hat鈥檚 where the ice meets its end. It either calves off as an iceberg, or it's melted from beneath by the ocean.鈥�
This is the natural fate of all glacier ice. The problem comes when more ice is lost to the ocean than is replenished from snowfall, which is now happening at Thwaites on an epic scale.
Since 2000, the glacier has lost more than a billion tonnes of ice, and this rate of loss has doubled in the past 30 years. The big worry is that, if it collapsed entirely, it could ultimately trigger a wider collapse of the ice of the entire West Antarctic ice sheet, causing a calamitous sea-level rise of more than 3 metres, on average, changing the coastline of the entire planet.
This glacier has long been an enigma. It was first sighted from the air in 1940 by an expedition led by US Admiral Richard E. Byrd and was the last part of Antarctica鈥檚 coastline to be mapped in detail.
Scientists first set foot on Thwaites in the late 1950s, and even now only a few hundred people have visited it. 鈥泪t鈥檚 an incredibly remote area. Very few people had been to the glacier itself or even close to its front on a ship,鈥� says at BAS.
The nearest research station, the UK鈥檚 Rothera base, is about 1600 km away, so it is no surprise that it can take more than a month to get to a fieldwork site on the glacier. 鈥泪t's such a long journey to get down there,鈥� says , also at BAS. 鈥泪t feels miraculous when all of the moving parts align and you actually get there.鈥�
The journey to Thwaites
To get to Thwaites glacier by plane, researchers flew to Christchurch and then on to the US Antarctic research station on Ross Island.
鈥淵ou need the weather in West Antarctica and Thwaites glacier to be good enough for a ski-equipped aircraft to fly from McMurdo into the field and then back again safely,鈥� says Davis. 鈥淪o we can spend a month or so at McMurdo waiting for the weather window.鈥�
From McMurdo, researchers flew to a field camp at the top of Thwaites glacier called the West Antarctic Ice Sheet Divide, landing on the ice. From there they got into a ski-equipped aircraft, a Twin Otter, and it鈥檚 only another few hours of flying down the glacier to get to the field site, close to where the ice meets the ocean.
The flight down the glacier is 鈥渏ust magical鈥�, says Maclennan. At first the surface is smooth, then cracks emerge as you approach the grounding zone where the ice goes afloat.
Getting to the glacier by ship isn鈥檛 straightforward either, and there are routes from both New Zealand and South America. 鈥淵ou quickly get the idea you鈥檙e going to a very remote place when you realise the ship has left South America and is going to take more than a week to get to the area,鈥� says Larter.
Researchers can visit Thwaites glacier for only a brief window of time in the summer, when conditions can actually be quite pleasant (considering it鈥檚 Antarctica), with temperatures sometimes even creeping above zero. In the depths of winter, however, it can get as cold as -51掳 C – and that鈥檚 without factoring in windchill.
It is a lonely place to be, save for the occasional visiting bird. 鈥淎t first, we felt very alone, because there was nobody for miles. And about a day after we had set up our field camp, three skuas [seagull-like birds] arrived,鈥� says Maclennan. 鈥泪 have no idea how they found us.鈥�
"If you wanted to choose a harder place to work in, you probably couldn鈥檛"
Occasionally, when researchers are working close to the ice front, Ad茅lie penguins will also pay a visit. 鈥淭hey will wander right into the middle of the camp just to see what's going on,鈥� says Davis.
鈥淥n a good day 鈥� the slang term is a Dingle day 鈥� when there is blue sky and absolutely no wind, it鈥檚 incredible,鈥� he says. 鈥淵ou could almost be wearing a T-shirt, because the sun is so strong and it's reflecting back off the snow at you.鈥� But such days are rare, especially as this part of Antarctica is known for its storms.
鈥淥n really bad days, you don't leave your tent. The winds could be up at 40 to 50 knots. There's blowing snow and zero visibility,鈥� says Davis. 鈥泪f you leave your tent, there'll be rope set up to get you to the toilet tent or to the mess tent. You'll have your snow goggles on, and you'll be completely wrapped up, because otherwise every part of your clothing gets filled up with that blowing snow.鈥�
鈥泪f you wanted to choose a harder place to work in, you probably couldn鈥檛,鈥� says , a glaciologist at Penn State University. 鈥淭he storms are epic.鈥� Ironically, it is the warm days that researchers are most worried about, as these signal the glacier鈥檚 demise.
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Why Thwaites matters
The world is already experiencing significant sea-level rise due to climate change, with things poised to get worse in future. And it turns out that the vast Thwaites glacier is the part of Antarctica with the strongest impact on projections of global sea-level rise, as it is changing the most rapidly. This makes understanding this glacier a top priority for the future of our planet.
鈥淲hat happens in Antarctica does not stay in Antarctica. It affects everybody. It affects everything,鈥� says Davis. 鈥淥ne of the hardest things to envisage is that something that the vast majority of people will never see 鈥� this sleeping giant of ice 鈥� can have such an impact on our everyday lives.鈥�
Until recently, most of what we knew about this glacier was gleaned from satellite images that sounded the alarm over its accelerating ice loss.
鈥淲e see it slowly collapsing before our eyes,鈥� says at Dartmouth College in New Hampshire. The front of the glacier, where the ice flowing from the continent meets the sea, is rapidly retreating inland.
Thwaites glacier is the 鈥渨ild card鈥� in the climate models, say at the University of Colorado, Boulder. 鈥泪t has the potential to dramatically change what sea-level rise will look like.鈥�
The latest projections from the Intergovernmental Panel on Climate Change give vastly different scenarios for sea-level rise depending on greenhouse gas emissions pumped into the atmosphere. These range from around half a metre by the end of the century (compared with 1950 levels) to a 鈥渨orst-case scenario鈥� of almost 2 metres if runaway collapse takes hold in the polar ice sheets.
What鈥檚 more, this loss of ice from Antarctica will disproportionally raise sea levels in the northern hemisphere due to a strange gravitational effect.
All this means that finding out how quickly Thwaites glacier is collapsing, and how much ice it will spew into the ocean under different climate scenarios, is crucial. But until a few years ago, little was known about the mechanisms driving the glacier鈥檚 retreat, such as the melting of the glacier ice by the relatively warm seawater.
鈥淲arm in this context, in this region, is about 1掳C,鈥� says Larter. This might not sound warm, but it is around 3掳C above the freezing temperature of seawater, and this temperature difference has a huge impact. So, the seawater that circulates around Antarctica is actually a vast reservoir of heat energy.
Revealing Thwaites's secrets
To find out exactly how this is playing out, observations in the field were needed.
In 2018 the first scientists of the International Thwaites Glacier Collaboration 鈥� a $50 million, seven-year, joint US-UK project 鈥� travelled to this remotest of places to begin to unlock the secrets of the vast body of ice by collecting data from above, below and around the glacier. This meant drilling right through the ice, inspecting the bottom of the floating ice sheet with a robot submarine and even deploying seals to measure seawater temperatures.
To understand how the sea around Thwaites glacier contributes to the melting of its ice, researchers recruited some surprising aides: the local seals.
"We want to have animals that dive deep," says at the University of St Andrews in the UK. Elephant seals dive easily to 1.5 to 2 kilometres, he says, whereas Weddell seals go down to around 400 to 500 metres. This makes them ideal for measuring how the deep layer of relatively warm water in the ocean surrounding Antarctica 鈥� known as the circumpolar deep water 鈥� flows towards the glacier.
These animals also provide year-round temperature measurements from places impossible to reach by boat, and when the ice or cloud cover prevents satellite measurements. For instance, the seals helped researchers to understand how currents driven by melting ice help prevent the warmer ocean waters from further melting the ice shelf.
Boehme and his colleagues use glue to attach sensors to the fur on the heads of the animals by jumping from a boat onto floating ice where the seals rest. The sensors are attached after the seals' annual moult, when the animals lose and then regrow all their fur. These tags, each costing around 拢5000, provide thousands of dive profiles, but because of the moult they eventually fall off. "We don't get them back," says Boehme.
(Picture: BAS)
Icefin is an underwater robot specially designed to explore the waters underneath the polar ice shelves. Shaped like a pencil, 3.5 m long and weighing 130 kilograms, Icefin is lowered through a hole in the ice 700 m deep, created by hot-water drilling.
"It takes about 24 to 36 hours from starting [to drill] at the surface to breaking through at the ice base," says Peter Davis at BAS. "You have to be quick鈥� the hole is always trying to refreeze."
Icefin is unlocking the secrets of the all-important grounding zone 鈥� the point where the glacier goes afloat to become ice shelf. The robot provides glimpses of the life under the ice, too. "There's no light penetrating the 700 m of ice, but there's always some invertebrate," says Davis, "or something on the rocks or the seabed, or living in the ice itself."
(Picture: Icefin/Schmidt lab)
The bedrock that lies beneath Thwaites glacier holds the key to whether it tips into a runaway state of ever-increasing collapse, as it provides resistance to the flow of the ice sheet. Building a clear picture of this hidden landscape is crucial.
To do this, researchers used radars to see below the ice and dragged machines on a 200-km journey along the ice to carry out seismic surveys of the glacier bed 2 km below. "What we've been trying to understand鈥� is what the bed is made of in terms of both the topography – the undulations – and also the materials that it's made of," says at BAS. "So, whether you've got a soft sediment that allows the ice to flow readily, or a stiff, hard bedrock that is much higher friction and that prevents the ice from flowing quite so quickly."
(Picture: Alfred-Wegener-Institut/鈥婳le Zeising)
After seven years of intense study, Thwaites glacier has revealed many of its secrets. One key question surrounds the stability of the floating ice shelf that protects the glacier.
Here, the news is not good. The last remaining area of the shelf in front of Thwaites, currently covering more than half of the 120-km-wide front, is expected to break away any day. 鈥泪t is tearing away from the glacier as rifts open close to the grounding line,鈥� says Larter. 鈥泪ts final demise could happen suddenly.鈥�
Even worse, the loss of buttressing due to this fracturing appears to have been causing an increase in the flow of the glacier upstream by an astonishing 33 per cent since 2020, meaning that more ice will pour off the continent into the sea. 鈥淭hat is for sure due to the tearing away of the ice shelf,鈥� says Scambos.
A view from space of Thwaites glacier
Robotic submarine missions to explore the underside of the ice have revealed a key factor driving this break-up. They discovered regions eroded into mysterious patterns such as swirls, clusters of teardrop shapes, or crevasses with terraced sides, and here the melting rates were particularly high. This, plus the discovery of huge undersea 鈥渟torms鈥� 鈥� vortices up to 10 km wide that become trapped under the ice 鈥� gives a detailed picture of how the ice gets destroyed by the sea, something predicted to get worse as the climate warms.
Another surprising discovery is the potent impact of tides. Height measurements made via satellite show the grounded ice of the glacier is lifted at high tides, drawing in warm seawater underneath and pumping it inland for 2 to 6 km, but an additional 6 km on particularly high tides. 鈥淭hat allows all the heat in that water to be expended on melting the ice, not just at the point where it goes afloat, but even a mile or two away from that edge,鈥� says Scambos.
This tidal pumping may provide a new explanation for the sensitivity of ice sheets to ocean warming, and an explanation for unexpectedly rapid rates of sea-level rise that have occurred in the past. 鈥淲e're still exploring just how important that process is,鈥� says Scambos.
These new insights are also helping to predict the likelihood of a worst-case scenario for rapid sea-level rise this century: dramatic ice loss due to runaway instabilities triggered in the glacier as it retreats.
"What happens in Antarctica does not stay in Antarctica. It affects everybody"
One of these doomsday scenarios may already be under way, since the glacier is situated on bedrock that gets progressively deeper inland, away from the coast. This geometry means that as the glacier retreats, it could lead to a rapid and self-sustaining collapse due to a process called marine ice sheet instability. 鈥淵ou鈥檙e losing some of the resistive force that holds the glacier back, so it鈥檚 the retreat itself that is driving future retreat,鈥� says Larter.
This could trigger very rapid loss of ice. 鈥淎re we in that yet, or just approaching that? We don鈥檛 know yet,鈥� says Scambos.
Overall, the ever-increasing loss of ice from Thwaites glacier means that, by 2067, it is predicted to be discharging around 190 gigatonnes of ice into the ocean per year, comparable to the entire amount being lost by the whole of Antarctica today.
Given the potent impact this will have on future sea-level rise, it is crucial that we keep an eye on the unfolding collapse. Although the US-UK International Thwaites Glacier Collaboration has wrapped up, the Korea Polar Research Institute has stepped up to the plate, with funding for a staggering nine years. 鈥泪t鈥檚 a big commitment,鈥� says , who heads this project.
What鈥檚 more, the Korean researchers have an icebreaker equipped with two helicopters, which enables them to reach places inaccessible to previous researchers who relied on fixed-wing aircraft 鈥� to 鈥渟ee the unseen鈥�, says Lee, and fill the gaps in our understanding of Thwaites glacier. 鈥淲e use it to improve the model, to reduce uncertainties, to predict the future.鈥�
On 27 December last year, Lee and his team set sail for Thwaites to study the fast-moving middle part of the glacier, a treacherous region with many rifts and hidden crevasses. 鈥泪t was scary,鈥� says Lee, with the ice making loud booming noises as it moved.
Bad weather meant they had only a few days to use hot-water drilling to make a hole almost a kilometre through the ice, close to the all-important grounding zone. Here, they found evidence of rapid ice melting by seawater. However, their aim to deploy a long-term monitoring device to the underside of the ice was thwarted when it became stuck as the researchers lowered it down the hole. They will go back in four years鈥� time to try again.
How doomed is the doomsday glacier?
Now that we have finally got a fuller picture of so many aspects of Thwaites glacier, what鈥檚 the lowdown on how doomed it really is?
The news is dire. 鈥淭he geography of the area and the characteristics of the ocean are going to lead to a rapid and catastrophic loss of ice from West Antarctica,鈥� says Scambos.
Computer models are revealing how this catastrophe will play out 鈥� and, crucially, the timescale. The ice flow is currently held back by rocky ridges in the bedrock, but once the glacier edge retreats beyond these points, the retreat will accelerate. 鈥淪tarting from about 80 years from now, things get pretty dramatic. In the second century [from now], it鈥檚 a definite catastrophe,鈥� says Scambos.
We can still buy some time. The computer models show that the speed of collapse depends on the levels of greenhouse gases in the atmosphere. Under high-emission scenarios, it could take around 100 years for the glacier to go beyond the final bedrock anchoring point, after which runaway ice collapse takes hold, but under low-emission scenarios, this time frame could be increased to more than 500 years.
"It鈥檚 a question of slowing it down to a manageable pace, so that it鈥檚 a millennium before we see 2 m of sea-level rise, rather than a century,鈥� says Scambos. 鈥泪t鈥檚 terrible to think about.鈥�
