THE largest glacier in the French Alps, the Mer de Glace near Mont Blanc, is melting faster than at any time in its recent history. The discovery is the first to be made with a technique for monitoring changes in glacier thickness based on satellite data alone.
Etienne Berthier from LEGOS (the Laboratory for the Study of Geophysics and Oceanography from Space) in Toulouse and colleagues used stereoscopic pairs of satellite images dating back to 1979 to monitor changes in the height of the Mer de Glace. The images showed that below a height of 2100 metres the glacier has increased its thinning rate from around 1 metre per year between 1979 and 1994 to around 4.1 metres per year between 2000 and 2003. The result confirms the fears of local people who have been adding more steps each year to the staircase that leads down to the glacier from a cable car station above.
The team calibrated the satellite data using ground surveys and aerial photos of the glacier. The technique can be used to monitor large, remote glacial areas that cannot be surveyed from the ground. Given that glaciers are considered reliable indicators of climate change, the team says the technique could help estimate the pace of global warming.
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