All three principal routes to Europe’s highest mountain have become impassable this summer. Now a veteran Chamonix guide says the heat stored in the rock could keep conditions deteriorating, and fears another 25 classic routes may also be lost.
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MONT Blanc has been effectively closed to most climbers.
It is an extraordinary position for Europe’s highest mountain to be in, but after weeks of exceptional heat, all three of the principal routes to the summit have become impassable.
Guides on the French and Italian sides have suspended summit attempts, while the Tête Rousse and Goûter refuges on the French normal route were closed on August 11 after repeated rockfalls made the approach increasingly dangerous. The Italian route had already become impracticable because of extensive crevassing.
The immediate question might be ‘When will Mont Blanc become climbable again?’, but there’s a more alarming question on the back of it… What happens if next summer looks like this one?
There is no suggestion yet that Mont Blanc will be closed in 2027, but the inference among the authorities is certainly there, and the events of this summer have raised a possibility that would have seemed extraordinary only a few years ago. And that possibility – that another prolonged period of extreme heat could leave the mountain with so few safe routes that climbing becomes impossible for an extended period – could very easily become a stark reality.
For Frédéric Bréhé, a Chamonix guide with 25 years’ experience, the signs are already deeply concerning.
“The heat stored by the rock will continue to melt the permafrost and prevent the situation from improving,” he told Le Monde.
That is not a problem that disappears simply because the temperature eventually drops, and the scale of what has happened this summer is difficult to overstate. For six cumulative weeks since June, the freezing level across the Mont Blanc massif has risen to between 4,200 and 4,500 metres. The average August freezing level between 1991 and 2020 was around 3,800 metres.
That difference has profound consequences at altitude. Ice has melted earlier, glaciers have become increasingly crevassed and sections of rock that would normally remain frozen have been exposed to sustained above-freezing temperatures.
Ludovic Ravanel, a geomorphologist at the Edytem mountain research laboratory, believes the mountain has reached a new level of instability.
“We have really crossed a threshold,” he explained, adding he had not expected to see conditions like those of this summer for at least another decade.
Ravanel’s research has examined around 2,500 rockfalls involving more than 100 cubic metres of material between 2007 and 2024. His work has found that such events are becoming both more frequent and larger.
This summer has provided a particularly dramatic demonstration. At least 10 rockfalls involving more than 100 cubic metres were being recorded each day during the worst period, according to Chamonix mayor François-Xavier Laffin, while around 15,000 cubic metres of rock fell from the north face of the Aiguille du Midi on August 12, according to Ravanel.
The underlying problem is the thawing of high-altitude permafrost which acts rather like a natural adhesive in the mountain, with ice occupying cracks in the rock and helping to hold unstable slopes together. As that ice disappears, the rock becomes more vulnerable to collapse.
And the process is not necessarily going to stop as soon as the heatwave does.
Perhaps nobody has a better feel for what that means on the ground than Bréhé.
The veteran guide says the heat stored in the rock would continue to drive permafrost thaw and make it difficult for conditions to recover quickly. He has also watched the number of viable climbing routes across the massif shrink dramatically.
The comparison he makes is extraordinary. In 1973, legendary French mountaineer Gaston Rébuffat identified 50 outstanding routes in the Mont Blanc massif. When Catherine Destivelle set out to climb the 100 finest routes in the massif in 2025, Bréhé says she could repeat only around half of Rébuffat’s original selection because the others were no longer accessible.
After the summer the Alps have just experienced, he believes another 25 could potentially disappear from the practical list.
That would leave only around a quarter of Rébuffat’s original routes from half a century ago.
For Bréhé, the deterioration has been so rapid that he said: “I aged 10 years in a single summer.”
It’s a sentence that says something important about the difference between a mountain becoming temporarily difficult and a mountain undergoing a fundamental change.
Mont Blanc’s Goûter route
The most obvious example has been the normal route from Saint-Gervais.
The Goûter corridor has always been a serious section of the ascent, with climbers crossing beneath unstable rock where falling stones are a recognised hazard. But this summer the danger became severe enough for the local guide companies to suspend Mont Blanc ascents and for the mayor of Saint-Gervais to close both the Tête Rousse and Goûter refuges.
The decision followed a succession of rockfalls. On August 11, 21-year-old climber Thomas Bordet was descending with a group when they experienced a major rockfall. He described hearing a deep rumble before the mountain began shaking and rocks, some reportedly as large as cars, came down around them.
The group took shelter against the rock face for several minutes before attempting to continue, only to encounter further rockfalls.
Jean-Marc Peillex, the mayor of Saint-Gervais, immediately said climbers should abandon their plans rather than expose themselves – and mountain rescuers – to unnecessary danger.
In announcing the closure, he wrote that the mountain and natural environment dictate their own rules and that climbers must show humility. There was little ambiguity in the message.
And yet, within days, 32 climbers who had begun their ascent before the closure found themselves at the Goûter refuge and sought helicopter evacuation, creating another controversy over the responsibilities of people attempting the mountain in dangerous conditions.
That episode may become particularly relevant if conditions like these return next summer.
What if 2027 brings another heatwave?
This is where the story moves from an extraordinary summer to a genuinely uncomfortable question.
Nobody can say with certainty what conditions Mont Blanc will face next summer. A cooler season could allow some routes to recover, and some of this year’s closures are temporary responses to particularly dangerous conditions.
But the mountain’s underlying problems are not temporary in quite the same way. The permafrost has been warming, glaciers have retreated, crevasses are changing, and rockfalls are becoming more frequent and larger.
And Bréhé’s warning is that the heat absorbed by the rock will continue to affect the mountain.
That means the question for guides isn’t simply whether Mont Blanc will reopen, it is whether the window in which it can safely be climbed is becoming shorter, less predictable and increasingly dependent on a few weeks of favourable conditions.
Bréhé’s answer to that changing reality has so far been adaptation. He knows guides can change the season, the routes, and even present different objectives. But he’s also aware that strategy has a limit.
Is Mont Blanc a shrinking mountain?
This is perhaps the most extraordinary aspect of current research. Mont Blanc itself isn’t getting any lower, and the summit isn’t disappearing.
But the mountain that climbers encounter is becoming increasingly different from the one described in the guidebooks and celebrated in generations of mountaineering literature. You only need to look at the routes themselves for evidence.
A line that was climbed repeatedly for decades can become too dangerous because a glacier has retreated, a crevasse has opened or the rock beneath it has lost the frozen structure that once held it together.
That is how a mountain can remain physically present while becoming, in practical terms, a different mountain.
Bréhé says that guides have to adapt, changing both the season and the objectives. He still talks about the importance of sharing their love of the places in which they work.
It isn’t a declaration that mountaineering is finished, but rather an acceptance that mountaineering has to change.
So, could Mont Blanc close next summer?
Yes. That prospect genuinely cannot be ruled out. If conditions were to deteriorate to the same extent, a prolonged closure would be entirely conceivable.
But that is an inference from this summer’s events, not an announced plan for 2027.
What we know is that Mont Blanc has already reached a point where all three principal routes became unusable at the same time. Local guides stopped offering the summit, refuges were closed and authorities intervened because the risks had become unacceptable.
We also know that the underlying conditions have not simply vanished.
And we have a guide with a quarter-century of experience looking at the mountain and saying that the situation may not improve quickly, while estimating that another 25 classic routes could effectively have disappeared from the repertoire.
That makes next summer’s weather rather more significant than the usual question of whether the Alps will get a good climbing season.
If 2027 is cooler, climbers will return. If it isn’t, Mont Blanc may face a decision that would once have seemed unthinkable. Not because the summit has become unreachable, but because there are no longer enough safe ways of getting there.
And that may ultimately be the most important lesson from our extraordinary summer of 2026.
The great mountains have never promised climbers a summit. Increasingly, we may now be facing a future where they may not even promise them a route.
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