(Bloomberg) -- The French village of Chamonix has been the thriving center of European mountaineering for more than three centuries. But climate change is upending the once-reliable seasons that underpin the region’s important tourism industry.

The Alps have warmed by about 0.5°C each decade since the 1980s, according to the Research Centre for Alpine Ecosystems. That’s made some of the most used routes more dangerous — and at times unclimbable — as rockfall increases and glaciers melt.

Story produced in partnership with Outrider Foundation

Photographs by Ben Tibbetts

While these changes might be imperceptible to the tens of thousands of alpine enthusiasts decked out in expensive gear who arrive every summer, mountain guides like Danny Menšík are starting to get worried. “Last summer was crazy,” he says. “It was the black summer for mountaineering in the Alps.”

Tourism makes up around two-thirds of Chamonix’s local economy. The town records more than 8 million overnight stays a year, generating €850 million ($900 million) in direct spending. Mont Blanc – the highest mountain in the Alps – is a huge draw, with more than 20,000 climbers a year paying around €2,000 each for a three-day guided tour to the summit.

Conditions got so bad in 2022 that mountain guiding associations including Compagnie des Guides de Chamonix, the world’s oldest, stopped offering to lead groups up Mont Blanc’s most popular Goûter route for several weeks during peak season. The mayor of St. Gervais, the municipality through which the route runs, proposed that climbers who ignored the warnings should have to pay a €15,000 deposit to cover possible rescue and funeral costs.

Things are set to get worse as temperature records continue to be broken. In August, a heat wave spread across the Alps, bringing the freezing point to 5,298 meters, almost half a kilometer higher than Mont Blanc. Both the Swiss and Italian routes up the Matterhorn have closed recently during hot periods. The Jungfrau in Switzerland, and the Dent du Géant (Giant’s Tooth), another classic route above Chamonix, have frequently been deemed too unsafe to climb.

Mountains are usually thought of as immovable, yet they are increasingly shifting and being reshaped as temperatures rise. Over the past two years, Mont Blanc has shrunk by more than two meters (6.5 feet) as its ice cap has melted. That’s leading to dangerous rockfall as the permafrost layer — which acts like an icy glue holding high-Alpine slopes together — becomes unstuck.

About 35 mountaineers die in France every year. Ten percent of those deaths happen at Mont Blanc’s infamous Grand Couloir du Goûter, a 100-meter wide gully that funnels falling rock toward the trail below. Every climber attempting the summit via the Goûter route must traverse the Grand Couloir.

While the odds of an accident are low for recreational climbers, “if you do that 20 times a summer for 20 years, then you really do accumulate quite a lot of risk,” says guide and photographer Ben Tibbetts.

I climbed Mont Blanc in 2019, and the Grand Couloir was the only point where my guide became visibly nervous. About 30 seconds before we were supposed to cross, a warning cry rang out from above: “Attention!” Rocks began to pelt the gully, like neolithic cluster munitions shattering into shrapnel. When the cascade ended, we rushed to the other side. Safely across, my guide turned to me and told me about a climber he’d once seen stopping in the middle to collect water. “A rock hit him, and he exploded.”

When Compagnie des Guides de Chamonix stopped guiding Mont Blanc during the heatwave of 2022, it was because this gully had become too dangerous to cross. The safest strategy is to attempt to traverse it before sunrise, when the air is coldest and the daytime melt has had a chance to refreeze. But even this tactic fails when nighttime temperatures remain above zero.

“Without the cold, without the snow and ice, the risk just rises exponentially,” says Menšík.

Alpine glaciers will lose half their ice by 2050 even if the planet warms less than 2C from pre-industrial levels,  according to a study published in the journal of the European Geosciences Union. Mid-19th-century photographs of Chamonix show Mont Blanc’s Bossons Glacier meeting the edge of the present-day town. Today the glacier hangs hundreds of meters above Chamonix; where there were once cliffs of ice now sit rows of chalets.

Nowhere is this problem as visible as Mer De Glace, France’s largest glacier. In 1909, a train line was built to take tourists to a station positioned on an overlook just above the ice, from which they could descend a short distance to reach it by foot. In 1988, the glacier had shrunk so much that a gondola was opened to ferry passengers to the ice. As the ice continued to recede, a staircase was added. That now has over 500 steps, necessitating a new, longer gondola that will open in December to accommodate the roughly 350,000 tourists who visit each year.

As glaciers shrink, familiar mountain routes change, new crevasses open, and rock faces once covered with ice are exposed, leading to more rockfall. In the worst-case scenario, glaciers can suddenly collapse. In July 2022, the day after double-digit temperatures were recorded at the summit of the Marmolada in the Italian Dolomites, an 80-by-25-meter block of ice sheared off the mountain’s glacier and killed 11 climbers. Eight more were hospitalized. In August’s heatwave, a glacier collapsed on the 4,027-meter Allalinhorn, killing one climber.

“It’s kind of counterintuitive, because there's nothing easier than walking on a glacier,” says Brad Carlson, a guide and ecologist for Compagnie des Guides de Chamonix, and lead author on its 2021 report Guides and Climate Change. “But from a risk management standpoint, it’s very full-on and serious, especially with the current conditions.”

In Chamonix, guiding companies are moving popular high-alpine tours to cooler months. While it used to be common for guides to take a spring break between the winter skiing and summer climbing seasons, many are now working all the way through, assuming it will be too hot in August to climb well-known peaks such as Mont Blanc and the Matterhorn.

While guides have been quick to adapt, other parts of the Alpine climbing infrastructure have been slower. “You can always find a hotel in Chamonix, there’s always some restaurants open,” says Carlson, but lifts and mountain huts have not yet shifted their opening dates.

Mont Blanc tours made up 60% of summer business for Compagnie des Guides de Chamonix as recently as 2017, but the company has been forced to diversify as the climbing season has become less reliable. The most popular summer activity now is a four-day training course that teaches mountaineering skills; just a third of its trips are to Mont Blanc.

“If you only focus on Mont Blanc, at some point you're going to meet the wall,” says Didier Tiberghien, the high-mountain director at Compagnie des Guides, who selects which tours the company offers. “It might be in two years, three years, five years, but it can't last forever.”

In May, the French Federation of Alpine and Mountain Clubs organized a meeting to discuss safety in the face of climate change. One idea mooted was to establish a formal rockfall forecast — similar to the avalanche forecasts that ski resorts use during winter.

Guides are already taking safety into their own hands. In French and English WhatsApp groups, hundreds of guides relay the conditions of their most recent climbs. Some double as researchers, studying how climate is impacting mountains, sharing their own rockfall forecasts and suggesting which altitudes and aspects of a mountain to avoid.

Tibbetts, who set up an English-language safety group, has devoted himself to exploring lesser-climbed mountains to devise alternative itineraries. But he acknowledges that visitors will continue to want to climb high peaks and popular routes, and that a tension will always exist between the desires of high-paying clients and safety-minded guides.

“The economic pressure is, unfortunately, kind of pointing in the wrong direction,” says Tibbetts. “Guides need to do a job to pay the bills. And people want to climb routes, regardless of conditions.”

Carlson, the ecologist, says that if people are determined to summit a particular peak, they should be prepared to spend longer in the Alps so they can climb when routes are in the best possible shape. Here there may be an upside for guides, as local knowledge becomes even more important.

“More and more, guides will be needed in the mountains,” says Tiberghien. “Because it's becoming more difficult to read the mountain.”

Story produced in partnership with Outrider FoundationPhoto editing by Jody Megson

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