The athletes' half-hour commute in the Swiss Alps – up two gondolas, then through a tunnel in the world's highest underground train to a glacier at 11,000 feet – served up daily grim reminders that global warming is threatening their line of work.

After exiting the train, they squelched through a field of greyish mud to reach shrinking snowfields scarred by new crevasses. Occasionally, they heard the sharp roars of glacial ice breaking off in monster chunks, then echoing across the peaks where they trained jumps, tricks and turns for the Pyeongchang Olympics. Most days, they basked in brilliant, snow-melting sunshine that bathed the whole scene in deceptive beauty.

Another subtle but telltale indicator of climate change's disruptive impact on winter sports: Many athletes – here 5,000 miles (8047 kilometres) away from the Rockies and 3,500 miles from the Green Mountains of New England – had the letters "USA" emblazoned on their jackets. Americans once had little need to swap continents to guarantee off-season access to snow. But warming is forcing athletes to hunt farther from home for wintry conditions, particularly just months away from an Olympics.

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"Without the snow and the cold in the places in the States where it's normally cold, we have to travel over here and find a place on a glacier to get a couple of jumps off," said Jon Lillis, world champion in aerials skiing. "Something that terrifies every winter athlete daily is the fact that the conditions are not as good as they used to be. You see videos of people skiing on glaciers back in the eighties and seventies, and half of that glacier doesn't even exist any more."

Last year, the aerials team stopped water training at its headquarters in Park City, Utah, in mid-October, then sat and waited a month for snow that came late to the mountain that hosted the Winter Games 15 years ago. The World Cup season began in China, and the Americans were forced to travel there not having set foot on snow in months. The results, not surprisingly, were dismal: not a single podium and only one finish in the top 5.

Lesson learned: This season, they uprooted to glaciers at Saas-Fee, Switzerland, and Ruka, Finland, for autumn training needed to be competitive at February's Winter Games in South Korea.

U.S. aerial skiing world champion Jon Lillis poses during an interview on the glacier above Saas-Fee, Switzerland.

The hunt for off-season training spots like these is increasingly a scramble, and not just for the Americans.

The hellishly named "Lucifer" heat wave that baked Europe in July and August wreaked havoc on teams' schedules. Canadian skicross racers had to cancel plans to train on Italy's Stelvio glacier that turned a sickly grey, rerouting to Mount Hood, Oregon, instead. Canadians endured issues elsewhere, scrubbing a planned summer training trip to Argentina because of hostile weather and extreme winds.

France's moguls team cut short a July training camp on its home glacier in Tignes after a crevasse opened under the course, which this year had just one jump instead of the usual two because of a shortage of snow, team member Ben Cavet said.

He was shocked by the visible deterioration of his regular venue for summer training.

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"It's crazy, you know? I always thought global warming was like your granddad going, 'Oh, I used to go and ski here 20 or 30 years ago and there was more snow,'" Cavet said in an interview. "But now we really are talking eight years. I can see a huge difference. Up on the glacier, now there's this huge cliff, you know, like a big rock, that you couldn't even see before."

"It is worrying, very worrying," he added. "What scares me about global warming is that you can see that the world is suffering in some of the most beautiful places on Earth."

Swiss aerial skier Mischa Gasser performs a jump during training on the glacier above Saas-Fee, Switzerland.

Other glaciers suffered, too.

Austria's Moelltaler Glacier closed from Aug. 15 to Sept. 7 because of what its operators said were "water gutters in the ice" and other safety concerns.

The Stubai Glacier, also in Austria, is deteriorating. U.S. coach Mike Jankowski, who brought some of the snowboarders and freeskiers there after the Saas-Fee trip, said there are concerns that some of the big buildings, drilled into the permafrost on the glacier, might not be stable for much longer.

Italy's Stelvio, billed as the Alps' largest summer skiing area, shut for 21 days in August, a sobering first since the opening of its lifts in the 1950s. Italian athletes who still came to train were hauled up on snowcats.

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"Partly it was because of the heat," said Umberto Capitani, in charge of the ski area. "But it's also been three years that we've had very little snowfall."

The Horstman Glacier in Whistler, Canada, near the 2010 Olympic Alpine venue, has deteriorated so badly that a renowned recreational snowboard camp was cancelled , and other activities curtailed.

"There used to be, like, nine lanes for different camps there, and now it's five or six," U.S. moguls skier Troy Murphy said. "We still go there. It's still pretty good. But the amount it's shrunk, the snow is so much lower."

Glaciers of the French Alps lost an average of 25 per cent of their surface area between 2003 and 2015, and the rate of shrinkage nearly tripled, according to a study being readied for publication early next year.

French researcher Antoine Rabatel said it is "highly probable" that the same trends will show up at glaciers elsewhere in Europe, as winters get shorter and summers hotter.

Winter sports training, he said, is "going to become harder and harder."

U.S. coach Todd Ossian readies one of the jumps for aerial skiers.

The quest for reliable spots is becoming more competitive and securing training locales is increasingly using up coaches' time and budgets.

"I need to be progressive and search out new spots," said Jankowski, who has had to add more reliable European venues to a global travel schedule that already includes trips to New Zealand and other locations in the Southern Hemisphere.

In October, skiing and snowboard athletes from the United States and dozens of other countries lined up before dawn, doing warmup exercises in the dark as they waited, to squeeze aboard the first gondola up to Saas-Fee's glacier. It also is in retreat, no longer reaching down to above the no-cars-allowed resort town, as it did in the 1930s.

Environmentally minded athletes are wrestling with the moral dilemma of contributing to atmospheric pollution with their widening search for snow.

"We take planes to go overseas. We take cars every day to go training," said French snowboard-cross racer Pierre Vaultier, gold medalist at the 2014 Sochi Games. "We are not examples about how to decrease global warming."

U.S. gold-medal snowboarder Jamie Anderson said it's easy to get "sucked into the system, whether you want to or not."

"It's hard to get out until you consciously make the decision," Anderson said. "With how passionate I am about snowboarding, it's hard to make that shift."

Well aware of the impact snow sports are having on the environment, Burton Snowboards recently announced a series of changes aimed at diminishing its environmental footprint.

The growing frequency of warm winters has, indeed, hurt the financial health of the industry, including ski resorts that form the backbone of the recreational side of the sport. A study commissioned by the Natural Resources Defence Council and the athletes' group Protect Our Winters found that skier visits in New Hampshire were 17 per cent lower and ski resort revenue was $54-million (U.S.) less in the "low-snow" winters of 2001-02 and 2006-07, as compared with higher snowfall winters of 2007-08 and 2008-09. The differences between low – and high-snow seasons in Colorado were 8 per cent in visits and $154-million in revenue.

A skier performs a jump during training on the glacier above Saas-Fee, Switzerland.

The increased frequency of warm-weather race disruptions on the pro circuits also is causing alarm. Mild temperatures and lack of snow in Germany, Croatia and Michigan hit the 2015-16 season with multiple cancellations and venue changes. Last season began with events in Colorado and Alberta scrubbed because of lack of snow. This season's early Alpine event in Beaver Creek, Colo., was run on almost all man-made snow that turned glassy in the warming sunshine.

Biathlon venues such as Ruhpolding in Germany and Ostersund, Sweden, commonly now make thousands of cubic yards of snow at the end of winter and store it through summer beneath tarps and wood chips for early-season races the next winter.

"We used to have relatively reliable conditions at all biathlon venues around the world," said Max Cobb, the president of U.S. Biathlon. "You can't count on it anymore."

Temperatures in the 40s and 50s greeted freestyle skiers and snowboarders at their world championships in Spain last March, creating mushy conditions like those that took some of the shine off the 2014 Sochi Games and the 2010 Olympics in Vancouver.

"It's a scary thing right now for winter sports. There's fewer and fewer places and all the glaciers are melting," U.S. aerials coach Matt Saunders said in Saas-Fee. "It's definitely getting harder and harder to get on snow early, for sure. We are having to travel further and further."

Scientists warn that worse is to come for winter sports, and that more warming will render proven Olympic venues unsuitable , even with greater use of artificial snow-making. Much has been said about the scarcity of snow in Beijing and surrounding areas, which will host the 2022 Winter Games, though officials have frequently brushed off the problem and promised to make enough artificial snow.

Park City is in the mix for the 2026 and 2030 Olympics. The irony is not lost on Olympians who live there but had to travel the globe to train for Pyeongchang.

"In my career, a lot of times, it's been really easy to chalk things up to it being a bad winter," said U.S. aerialist Mac Bohonnon. "But [warming is] undeniable. And the more I've travelled, the more I've seen that it's a pretty common theme wherever you go."