The world’s thickest glaciers may “calve” icebergs up to three times faster than previously predicted. However, such rapid retreat may not be sustained over long periods.

Instead, the large bodies of ice – which include Antarctica’s Thwaites glacier – may collapse in bursts, with intervening periods of stability.

The behaviour of tall ice cliffs is one of the biggest sources of uncertainty in predicting future sea level rise. Several of the world’s largest glaciers in Greenland and Antarctica extend out to sea, with their bases resting on the sea floor. Their coastal edges can form ice cliffs looming as high as 100 metres above the ocean’s surface.

For years, researchers have feared that such marine-based glaciers might be vulnerable to runaway cliff collapse. The idea here is that each time an ice cliff collapses, it exposes a new, taller – and so potentially even less stable – ice cliff further towards the glacier’s interior. The loss of ice due to runaway collapse of these ever-taller cliffs could , according to an Intergovernmental Panel on Climate Change report. But we don’t yet have enough empirical data to know how likely it is that runaway cliff collapse will occur, so previous studies have relied on ideal mathematical models to envision the process instead.

at the Massachusetts Institute of Technology-Woods Hole Oceanographic Institution Joint Program and her colleagues used satellite data to provide the first direct, large-scale observations of how the tallest ice cliffs actually behave, offering a firmer basis for estimating the danger of runaway collapse – and the rapid sea level rise that could result.

According to the study, the risk of runaway collapse depends on two main factors: how steeply the sea floor beneath the glacial ice deepens, and how quickly the ice flows seawards. Imagine an up-ended jar of thick honey spilling onto a plate: it won’t remain in a tall, stable shape, but will thin outwards at the edges. In a similar way, if the viscous flow of ice is fast enough, it will thin out the edge of a glacier, reducing cliff height. Even if the glacier is thicker further towards its interior, sufficiently rapid ice flow appears able to compensate, lowering those ice cliffs and preventing a runaway effect.

This idea has been suggested by idealised mathematical models, but had never been systematically measured in real glaciers. “None of the glaciers we observed underwent unstable retreat, even though they did retreat much faster than our current models predict,” says Needell.

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That retreat could speed up even further in the future. Needell notes that most glaciers in the study are “buttressed” by sea-floor features. For instance, a series of underwater ridges currently help stabilise Thwaites from beneath.

“Over the next decades, it’s going to jump from one pinning ridge to another,” almost like “tripping” downhill, says at the University of St Andrews in the UK. Eventually, Thwaites will reach a point where those ridges disappear. “The bed then begins to get real deep,” says Benn. At that point, which the glacier may reach within the current century, “the whole structural integrity of the ice becomes unviable”.

The ‘doomsday’ glacier’s giant ice shelf is about to break away

The floating ice shelf of world’s widest glacier – Thwaites glacier in Antarctica – is detaching, with worrying implications for global sea-level rise

That is when runaway collapse becomes a real possibility. However, those conditions may also speed up the flow of ice, thus thinning out any looming cliffs. The key question, says Needell, is whether thinning can outcompete rapid ice loss, restabilising the glacier. Her study suggests that it might – but the question remains open.

at the British Antarctic Survey points out that we haven’t yet seen this kind of runaway cliff collapse. One study suggests that it may have happened in the vicinity of Thwaites around 12,000 years ago. “The problem is, nobody was around to take observations at the time,” he says. “It’s a possibility we have to keep our eye on.”

About 1000 glaciers are now being lost every year and this rate could climb to 3000 per year as soon as 2040, even if countries meet their targets to cut carbon emissions.

At least 4000 glaciers have melted away in the past two decades. at ETH Zurich in Switzerland and his colleagues used climate models to predict what will happen to the world’s 211,000 glaciers in the coming century under different global warming scenarios.

Current climate goals put the world on track for 2.7°C of warming above pre-industrial temperatures this century. This would mean 79 per cent of the world’s glaciers will disappear by 2100. If humanity limits global warming to 2°C, however, 63 per cent of glaciers will disappear.

“We’re going to lose many of our glaciers, but we have the ability to preserve a lot of them as well,” says at Carnegie Mellon University in Pittsburgh, Pennsylvania, who worked on the study.

If countries don’t meet their targets and the world warms by 4°C, 91 per cent of glaciers will be lost.

Glacier melt is projected to sea levels by 25 centimetres this century. It will also undercut the summer melt that many regions rely on for irrigation. Two billion people live in drainage basins fed by mountain snow and ice, many near rivers originating from Himalayan glaciers.

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Melting ice also means that floods caused by a sudden release of water from a glacial lake are becoming more frequent, like the one that 55 people in India in 2023.

Previous research found that half of all glaciers would melt away this century even if humanity restricted warming to 1.5°C, the most ambitious Paris Agreement goal. This study upgrades those estimates, finding that 55 per cent would be lost with this amount of warming.

It also projects the rate of glacier loss by year and by region. This rate will peak around mid-century, then slow once smaller mountain glaciers are gone and bigger ones are left, such as in the Arctic and Antarctica.

“The larger ones, it just takes a lot of time to melt the ice, [so] they will disappear later,” says Van Tricht.

Under current climate targets, western Canada and the contiguous US will lose almost all glaciers by 2100. In a blow to tourism, Glacier National Park in Montana will be largely bereft of glaciers, although some could remain as miniature glaciers or ice patches, according to upcoming from the United States Geological Survey.

The Alps will also be almost bare. Communities are already holding funerals for glaciers, and the Global Glacier Casualty List is collecting their stories. at ETH Zurich, who worked on the study, and 250 other people climbed to the remains of Pizol glacier in 2019.

They came to say goodbye, but also to tell the public “we are attached to our glaciers,” says Huss. “If they are gone, it matters to us.”

As Greenland’s glaciers melt, water usually drains to the bedrock below before flowing out to the ocean. But in 2014, a huge torrent of meltwater from a subglacial lake burst out of the surface of the Greenland ice sheet, leaving 25-metre mounds of ice and giant crevasses in its wake.

“We haven’t observed anything like this before,” says at Lancaster University in the UK. “We know that lakes beneath Greenland drain. But what we’ve never seen before is this fracturing and the water actually erupting through the surface of the ice sheet.”

McMillan and his colleagues began to investigate after spotting the sudden appearance of a crater 85 metres deep in the surface of the ice sheet, captured by satellite in August 2014. They used satellite data and numerical models to reconstruct what happened to cause the crater.

They found the crater had emerged after the rapid draining of a subglacial lake within a 10-day period in July and August 2014. About 1 kilometre downstream from the crater, the team spotted a huge disturbance of the ice where the water had emerged.

The team believes the water pressure in the subglacial lake had increased enough to force it back above ground through fractures in the ice, eventually bursting out of the ice sheet and leaving huge crevasses and ice towers in its path.

The meltwater was forced upward because it was surrounded by ice frozen to the bedrock, explains McMillan. “What seems to have happened here is that when you put water into a situation where the ice was kind of frozen in the surrounding region, you could actually build up a lot more pressure, and you could cause this unexpected effect,” he says.

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McMillan now wants to identify whether similar eruptions have happened using satellite imagery, and whether this is a process driven by the ice sheet rapidly melting as global temperatures increase.

“This is a first view of a new phenomenon that we didn’t know existed before, and the challenge now is to understand the implications and the processes of that,” he says.

Glaciers worldwide have shrunk by more than 5 per cent on average since 2000, according to the most comprehensive assessment yet. This rapid rate of melting has accelerated by more than a third in the past decade as climate change continues apace.

“Any degree of warming matters for glaciers,” says at the University of Edinburgh, UK. “They are a barometer for climate change.”

The new numbers come from a global consortium of hundreds of researchers called the Glacier Mass Balance Intercomparison Exercise. The group aimed to reduce the uncertainty around how much the planet’s 200,000 or so glaciers have melted by using a standard procedure to assess different measures of their change in size. This includes gravity and elevation measurements from 20 satellites as well as ground-based measurements.

Between 2000 and 2011, glaciers were melting at a rate of about 231 billion tonnes of ice per year on average, the researchers found. This melt rate increased between 2012 and 2023 to 314 billion tonnes per year, an acceleration of more than a third. 2023 saw a record loss of mass of around 548 billion tonnes.

These numbers are in line with previous estimates. But this comprehensive look “provides a bit more confidence about the change that we see on glaciers”, says Gourmelen, who is part of the consortium. “And there’s a clear acceleration.”

Altogether, the thawing of around 7 trillion tonnes of glacial ice since 2000 has raised sea levels by almost 2 centimetres, making this melt the second biggest contributor to sea level rise so far, behind the expansion of water due to warming oceans.

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“This is a consistent story of glacial change,” says at the University of Washington in Seattle. “Regions that have had glaciers since time immemorial are losing these icons of ice.”

Glaciers in the Alps have lost more ice than any other region, shrinking by nearly 40 per cent since 2000. In the Middle East, New Zealand and western North America, glaciers have also seen reductions of more than 20 per cent. Depending on future emissions, the world’s glaciers are projected to lose between a quarter and half of their ice by the end of the century.

These striking images highlight Earth’s vanishing ice and the fight to save it. A staggering two-thirds of glaciers may disappear by the end of the century, threatening ecosystems and global water supplies. The images took some of the top prizes in the , run by UNESCO and Onewater. UNESCO has designated 2025 as the International Year of Glacier Preservation.

Julia Roger-Veyer received second place in the European category for her atmospheric shots of the Mer de Glace, France’s largest glacier, at Chamonix. The image above was shot from within a moulin, a huge hole carved into the glacier by meltwater, while the photo below peers inside a cave created by glacial retreat. Roger-Veyer climbs and photographs the Mer de Glace each autumn. Each year, the glacier retreats roughly 40 metres. In an announcement about her win, she said she expects she will “probably be a helpless witness” to its disappearance.

Michele Lapini captured first prize in the Europe category for his shot documenting the effort to save Presena Glacier in northern Italy (below). Vital to the alpine ecosystem, the glacier’s surface area decreased from 68 hectares to 41 between 1993 and 2003, according to Lapini.

In 2008, conservationists began spreading textile sheets over the glacier each summer to prevent melt. The photo shows a worker unhooking sheets during autumn before the first snow. The effort may have by two-thirds, but cannot pause ice loss. As Lapini writes, “climate change cannot be mitigated through localized quick fixes alone”.

The contest’s global prize is sponsored by MPB, its regional Asia prize is sponsored by Asian Development Bank, and its regional European prize by the city of Burghausen.