When Emmanuel Macron went to Chamonix (Haute-Savoie) in mid-February to see the Mer de Glace, he first began his descent to the frozen abyss by cable car from the Montenvers station. Then take the 500 steps built along the rock wall that leads to the glacier. A staircase punctuated by small plaques indicating how high the giant of the Alps was in previous years and showing how far it has receded over the centuries. "Impressive," had blown the President of the Republic. I never imagined a cast so fast. "
"Only thirty years ago, he would just have needed to take the gondola to touch it," explains Antoine Rabatel, glaciologist at the University of Grenoble-Alpes. And in 1850, he would almost have had the Mer de Glace at his feet where the arrival station is today ”. If the head of state went to the bedside of the largest French glacier, it is because he has become the symbol of global warming. "At the end of the Middle Ages, the Mer de Glace extended into the Chamonix valley near homes," says Benjamin Pohl, climatologist at CNRS. The glacier stopped near the little chapel of Les Praz and then backed off. "
VIDEO. The unconfined Mont Blanc
A fir forest has since covered the traces of its presence in the valley. When we had the opportunity to observe the glacier from below from the Torino refuge located at 3375 meters above sea level, on the Italian side, during our ascent to Mont Blanc, it was already only a shadow of himself with his grayish hue and his thin bed of ice. "In the past, it was rather white but it changes color because it carries a lot of sediment and is now covered with rocks, explains Benjamin Pohl. It is a glacier that is going badly. The bottom of the Mer de Glace has lost more than 200 meters in thickness since 1905, melting 5 to 10 meters per year in recent years.
Scientists expect the glacier at the foot of Mont-Blanc to lose another 30 to 40% of its volume by 2050. And under the most pessimistic scenario for greenhouse gas emissions considered by climatologists, the Mer de Glace could even disappear by the end of the century.
A disaster for the valley because the glacier in particular supplies water to the hydroelectric power station located above Chamonix. "We can fear a drop in the level of the Rhone in summer because the river is supplied with water by the Alps, details Benjamin Pohl. However, nuclear power plants need sufficient water flow to cool their reactors. "
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In the valley, the ski resorts are already worried about their winter sports season. "With the warming, it will no longer be certain between now and the end of the century to find good quality snow cover below 3000 meters", fears the CNRS climatologist. This is because rain will increasingly tend to replace snow.
"In the Alps, the snow cover period has already been reduced by forty days since the 1970s," adds geography researcher Jacques Mourey. Experts even expect “thaw” days every other day to culminate. "Even if the summit will remain covered with white and ice, the notion of eternal snow risks going from books of geography to books of history because the landscape will have radically changed, underlines Samuel Morin, director of the Center for Snow Studies . Some glaciers have already disappeared, others are retreating at very high speed, the shrubby vegetation is rising and some species are migrating at altitude. "
"Ice loses its cement effect"
Beyond this change of landscape, which climatologists consider irreversible, the Mont-Blanc massif is becoming an increasingly dangerous adventure terrain for mountaineers. “Warming makes conditions more difficult and uncertain, especially in the middle of summer because there is not enough snow and more and more rocky destabilization, explains Jacques Mourey. In the famous Goûter corridor, there have always been rockfalls, but more big events are expected at the end of the season. This is because the heat has a profound impact on permafrost (permanently frozen floors). "The ice is gradually losing its cement effect," deciphered the geographer.
"When heat waves occur, there are certain routes that we no longer take because of the risk of landslides," confirms the president of the National Union of High Mountain Guides, Christian Jacquier. We are even starting to train the guides to spot weak signals announcing large landslides on a wall. Especially when you spot water flowing in the cracks, it causes vibrations in the wall and weird noises inside the rock. "
The precedent of piz Cengalo
This work of monitoring the walls to prevent disasters is due to the geomorphologist Ludovic Ravanel. "We cannot say where it will fall or when, but we have designed a risk index for sectors with refuges and ski lifts potentially exposed to the melting of permafrost", explains the scientist.
Climatologists all have in mind the collapse of the Cengalo piz in Switzerland in late August 2017. More than 3 million cubic meters of rock collapsed at once, pulverizing the small glacier located below, causing a rock avalanche followed by 'a mudslide which destroyed part of the village of Bondo. A village fortunately evacuated in time. But a hundred buildings were destroyed and eight mountaineers and hikers who were on a closed path were killed. The Alps had not experienced such a collapse since 1717!
Conquer Mont Blanc in 6 episodes
1. Attacking the Roof of Europe
2. Shipping turns into a nightmare
3. A summit of difficulties
4. Subject to climate change
5. Yes, here it is polluted
6. Her secrets, young and old
