In Chamonix (Haute-Savoie)
Bathed by a bright sun, the thick layer of eternal snow sparkles with a thousand lights, shines as bright as a diamond, dazzling walkers and passing journalists. Magical view offered by Mont Blanc majestically overlooking the Chamonix valley. On Wednesday, the roof of Europe was at the heart of all discussions, even concerns. The reason: its peak has decreased by 2.22 meters in two years. And even 5 meters compared to 2001, when it peaked at 4,810.40 meters.
In the minds, the shortcut is quickly found. Without a doubt, if Mont Blanc is bending a little more, it is because of climate change. However, the specialists are much more cautious, starting with Jean des Garets, president of the departmental chamber of expert surveyors of Haute-Savoie. “In one night, 1.50 meters of snow can fall,” he recalls. Enough to distort the situation.
“Nothing alarming for the moment”
Looking more closely at the figures, the summit of Mont Blanc has continued to yo-yo, alternating ups and downs. But since 2013, the 4,810 meter mark has never been crossed again. “Between 2017 and 2019, we have already recorded a difference of 2.60 meters”, in turn supports Denis Borrel, expert surveyor for whom “there is nothing alarming for the moment”. “We know that from one week to the next, from one month to the next, the very altitude of the snow changes,” says glaciologist Luc Moreau. Global warming is not represented by this altitude because the summit is cold. It is -15°C on average all year round. There is no melting at the top of Mont Blanc. »
The “surprise”, on the other hand, is that the measurement taken on September 15 is similar to that recorded in the spring. “Usually, that of September is always higher,” observes Denis Borrel. Which means that “Mont Blanc did not recharge during the summer, as it usually does”, translates Farouk Kadded. “This is still the result of the lack of precipitation and the drought that we have been experiencing for two years,” analyzes Luc Moreau.
“Too early to make a connection”
“The size of Mont Blanc is not a marker of global warming but a trend,” he continues, specifying that the consequences are more visible at lower altitudes. “Because of very hot summers, we have observed a proven decrease in the height of glaciers for thirty-five years. The Bossons glacier, which is becoming increasingly black, has lost almost 30 meters in thickness in two years. » But it is difficult to say that the skull of Mont Blanc is the victim of overheating. “We do not have a permanent thermometer at the summit,” explains Luc Moreau. The highest is located at 4,300 meters, buried under sixty centimeters of snow. There, the temperature recorded was -11°C…. except the last time when the mercury rose two degrees. “There is still a link somewhere,” replies the glaciologist. But it is still too early to establish this. »
“For the glaciers, it’s clear. The mass balances show a real drop in their volume. But at 4,800 meters, we don’t know what’s happening. We have no regular measurement, no coring, summarizes Farouk Kadded. And climate change is seen over time. It is not in the space of a few years that we can draw conclusions. Even 22 years of hindsight for the climate is too little…” Reassured?