December 8, 2011
French Glaciers Have Decreased 26% In 40 Years
A new study has found that the glaciers in the French Alps have lost a quarter of their area in the past 40 years.
Marie Gardent, from the University of Savoie, and colleagues assessed about 600 glaciers in broad areas incorporating the Ecrins, Belledonne, Vanoise, Ubaye and Grande Rousse Arves massifs.
The team used map archives, past satellite imagery and aerial photographs to assess the areas. Manual inspection was used to ensure that the automatic delineation methods used in the pictures was accurate.
"We use manual delineation to verify the satellite data because there can be a problem with debris cover on a glacier," Gardent said in a statement.
"Automatic delineation from satellite data will sometimes say there is no glacier when in fact we know there is one there. Also, deep shadows can hide the glacier margins."
The only existing glacial inventory from the French Alps was published about forty years ago within the context of the World Glacier Inventory. It saw that the overall area of ice was about 144 square miles.
The new survey has found that glacial coverage has decreased to a value of about 131 square miles by 1985 to 1986.
The team said that the withdrawal has accelerated, and the area is now reduced to about 106 square miles.
The survey shows that an average loss of about 26 percent over the past 40 years has taken place in the French Alps glaciers.
The greatest losses have been seen in the southern sectors, with some areas almost completely disappearing. In the Ecrins Massif, glacial retreat is over three times stronger than in the Mont Blanc Massif.
The shrinkage in the northern Alps, where the biggest French glacier La Mer de Glace, has shrunk by just half a square mile to 11.5 square miles.
"The glacier retreat is less important in the northern Alps than in the southern Alps," Gardent said at the American Geophysical Union (AGU) Fall Meeting.
"We think this is because of the lower elevation of the mountains in the south, but also because of climatic conditions which are different. There is more precipitation in the north and there is also more cloud."
Swiss researchers reported at the AGU meeting three years ago that glaciers on their part of the European range were also losing mass at an accelerating rate.
On the Net: