The French Alps' premier ski destination, Chamonix, lies in the shadow of the Mont Blanc mountain range. Its snow-covered slopes give off a pristine glint in the sunlight. At its apex, Mont Blanc (15,781 feet) overlooks everything, a symbol of the resort's long, rock-ribbed traditions. It is the highest peak in Western Europe.
During the offseason, Chamonix has a population of 10,000. Come ski season, up to 80,000 visitors at a time throng into the valley. Last summer, local officials counted a record 100,000 visitors in a single day.
But concerns about air quality, as well as troubling, climate-related changes in the landscape of the surrounding mountains, are causing local government and conservation groups to rethink how much future tourism the delicate ecosystem can handle. The air pollution in the valley can get so bad, it rivals the worst cities in Europe.
Signs along the narrow roadway leading here tell part of the story. Every few miles, blue signs politely request that drivers reduce their speed by 20 kilometers per hour in order to limit vehicle emissions. But the polite requests are of questionable value. According to E.U. guidelines, maximum acceptable particulate matter (PM10) may reach a high of 50 micrograms per cubic meter for no more than 35 days over the entire year. In 2011, this soot count exceeded the 35-day maximum by March.
Chamonix has lured tourists in search of fresh air, virgin snow and recreation to its mountain resorts both winter and summer since the 18th century. The first Winter Olympics were held in Chamonix in 1924.
Since that time, the valley's mean temperature has increased by 1.5 degrees Celsius, twice the average worldwide increase. Snow accumulation has fallen to half of what it was 40 years ago.
Eric Fournier, the mayor of Chamonix, and mayors of the three other towns comprising the Chamonix Mont Blanc Valley Joint Local Authority have seen the writing on the wall. Together they have drawn up a Climate and Energy Action Plan and are dedicating themselves to reducing greenhouse gas emissions in the valley by 22 percent before 2020.
"We're looking to adapt tourism in the long term," Fournier said.
Keeping skiers in, cars out
"While we have to consider the investment in ski areas, we can't continue with the same kind of growth the valley saw during the last century," he added.
To combat pollution caused by vehicle traffic, the mayoral consortium has applied for E.U. funding to modernize the currently nonoperational Saint Gervais-Vallorcine train line, which runs between the Swiss border and the French Alps village of Argentière, a projected investment of €72 million ($92 million).
The eventual goal is to restrict vehicle traffic in the valley so visitors will have to travel by train and bus. By itself, a fully operational train line could reduce emissions: Cars cause 38 percent of greenhouse gases in the valley.
The consortium also wants to change the way residents heat their homes. Residential heating contributes 31 percent of total emissions. The consortium has begun offering grants to all year-round residents to convert to passive solar for home heating.
As for winter sports, the most important aspect of regional conservation, Fournier said, is to make sure the specific needs of the area are addressed by vendors and service providers.
This month, Fournier is reviewing competing bids from 30 companies for new ski area management contracts. He expects to see concrete plans for adaptation to climate change, improvements to the quality of the resort, and upgrades to lift machinery and slope grooming services.
His goal is to improve the quality and efficiency of the tourist experience and to cap the number of visitors.
"The main ski area, Les Grands Montets, has the best slopes in the world," he said. "Currently, there are nine lifts. Only seven will remain open. Seven optimally functioning lifts will be more efficient, more economical and more integrated with the environment."
The most important change in the tourist business will be stricter controls. "There will be no more new development in Chamonix," Fournier said. "Redevelopment, yes. But no more people can fit. The quality of the experience is the selling point here, not infinite accessibility."
Danger from above
Although the ski industry is pivotal to the health of the local economy, an expert on the changing mountain landscape, Ludovic Ravanel, director of the Office de Haute Montagne, has cause to question how long the mountains themselves are likely to last in their current condition.
Glacial retreat is one part of the picture: The Alps have lost more than half of their total glacial surface since 1862, the end of the Little Ice Age.
"Receding glaciers are easy to see with the naked eye, so people think they're the main problem," Ravanel said. "But rock permafrost changes, which are less visible than glaciers, pose a far greater danger to human activity."
Most of the Mont Blanc massif lies well above the permafrost line, which is at about 9,000 feet.
"At that elevation, the rock itself is always frozen. The ice in the cracks is like cement, holding the mountain together. Then if it thaws, it becomes unglued," Ravanel said. Because most of the range is well above the line, it remains frozen at temperatures ranging from minus 12 to minus 14 C. But the area between the 9,000-foot limit and about 12,000 feet is increasingly becoming more temperate. It thaws during the summer months and refreezes during winter.
Repeated melting and refreezing forces open the crevices and destabilizes the rock face. This leads to rock slides.
Since the end of the Little Ice Age, there have been 42 documented rockfalls on the north side of the Aiguilles de Chamonix. And they are increasing in frequency and severity: 70 percent of the rockfalls that have occurred here since the Little Ice Age have taken place in the last two decades and correspond with the acceleration of global warming. The worst year in the Alps in recent history for rock slides occurred during the heat wave of 2003.
More snow machines? 'Non-negotiable'
Not only are rockfalls increasing in frequency, but they are becoming more severe. In December 2011, a rockfall on Piz Cengalo in eastern Switzerland brought down up to 141 million cubic feet of rock. Before that, the largest single rockfall in the Alps occurred in 1717, the Triolet rockfall above the Aosta Valley, which brought down 565 million to 706 million cubic feet of rock and buried several buildings.
The Mont Blanc massif isn't alone when it comes to increasingly severe rockfalls. Last summer, a series of rockfalls in the Rocky Mountains in the United States and Canada brought down more than 1 billion cubic feet of glacier and granite.
As for the prospects for skiers and snowboarders, the news is both good and bad. The 2012-2013 ski season has been a success. The weather remained consistently cold, and it snowed a lot.
"We had no need for artificial snow," Fournier said. "This is a good thing." Only 17 percent of the slopes at the six major ski areas in the Chamonix area have snow making equipment, and they didn't use it at all this year. "We're going to limit use of snow making," Fournier said. "For the areas that don't have it, we will never allow them to have it. The use of snow making equipment is fixed where it is and is non-negotiable."
The picture for ski resorts in the southern Alps, which lie partly below the snow line, is less rosy. "Glaciers in the southern Alps, where the elevation is below about 10,000 feet, will disappear in the next two decades," Ravanel said.
Here in Chamonix, where more than 80 percent of the ski areas are above 10,000 feet, skiers don't have so much to worry about. For the short term, at least -- unless the mountains themselves crumble -- the grand winter sports tradition will live on.
Correction: A previous version of this story incorrectly called Mont Blanc the highest peak in Europe rather than the highest only in Western Europe.