and Climate Change
6 December 2011 Last updated at 20:24 ET
The Big Melt: French Alpine glaciers in rapid retreat
By Jonathan Amos Science correspondent, BBC News, San Francisco
In the Ecrins Massif, glacial retreat is more than three times
stronger than in the Mont Blanc region
Glaciers in the French Alps have lost a quarter of their area in
the past 40 years, according to new research.
In the late 1960s/early 1970s, the ice fields slipping down Mont
Blanc and the surrounding mountains of the European range covered
some 375 sq km.
By the late 2000s, this area had fallen to about 275 sq km.
The research has been presented at the American Geophysical Union
(AGU) Fall Meeting, the world's largest annual gathering of Earth
It mirrors some findings of retreat occurring in other sectors of
the Alps which sit across the borders of several nations, but
predominantly Switzerland, Austria, Slovenia, Germany, France, and
The new French Alps glaciers inventory was produced by Marie
Gardent, from the University of Savoie, and colleagues.
It assessed the roughly 600 glaciers in broad areas incorporating
the Ecrins, Belledonne, Vanoise, Ubaye and Grande Rousse Arves
massifs, as well as the famous Mont Blanc Massif in the north.
The team drew upon map archives, past satellite imagery and aerial
photographs. Manual inspection was used to check the automatic
delineation methods employed in the pictures was correct.
"We use manual delineation to verify the satellite data because
there can be a problem with debris cover on a glacier," explained
"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."
A great deal of effort is now going into monitoring the status of
The only existing glacial inventory from the French Alps was
published four decades ago within the context of the World Glacier
Inventory. It found the overall area of ice to be about 375 sq km.
By 1985-86, in spite of a short advancing period in the late
70s/early 80s, glacial coverage had decreased to a value close to
340 sq km, the new survey shows.
Since then, the withdrawal has accelerated, with the area being
reduced to about 275 sq km in the late 2000s.
Nasa's Landsat spacecraft looks down on Mt Blanc and La Mer de
Glace snaking off to the north-west
This represents an average loss of some 26% over the last 40
years. The retreat is not uniform across the French Alps, however.
The greatest losses have been seen in the southern sectors. In the
Belledonne Massif, for example, glaciers have almost completely
disappeared; and in the Ecrins Massif, glacial retreat is more
than three times stronger than in the Mont Blanc Massif.
"The glacier retreat is less important in the northern Alps than
in the southern Alps," Ms Gardent emphasised.
"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."
The northern region includes the biggest French glacier of all -
La Mer de Glace, which falls over a 1,000m in altitude down Mont
Blanc itself. Its area today is just over 30 sq km, a shade
smaller than the 31.5 sq km in the late 1960s/early 1970s.
Efforts to assess and monitor glacier health are going on across
the Alpine region.
At this very meeting three years ago, Swiss researchers reported
that glaciers on their part of the European range were also losing
mass at an accelerating rate.