Swiss researchers have confirmed that the country's glaciers have declined significantly over the past century, after research released on Monday showed the ice caps had lost half their volume since 1931.
Climate change has contributed to the rapid glacier melt in the Alps, much of which has been closely monitored since the early part of the century.
But the reduction of glacial volume had not been widely studied before this period, leaving scientists mostly in the dark over the true scale of the change.
Swiss researchers from the ETH Zurich technical university and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL say they had now reconstructed the topography of all Swiss glaciers in 1931, making it possible to demonstrate how they have evolved.
"Based on these reconstructions and comparisons with data from the 2000s, the researchers conclude that the glacier volume halved between 1931 and 2016," the researchers said in a statement.
Their study, published in scientific journal The Cryosphere, used material from the Terra image archive, which covers about 86 per cent of Switzerland's glacial area, analysing about 21,700 photographs taken between 1916 and 1947.
For their reconstruction, the glaciologists used so-called stereophotogrammetry — a technique used to determine the nature, shape and position of any object on the basis of image pairs. "If we know the surface topography of a glacier at two different points in time, we can calculate the difference in ice volume," lead study author Erik Schytt Mannerfelt said.
The researchers presented side-by-side picture pairs showing the same spot nearly a century apart, indicating the dramatic change that has taken place.
The Fiescher Glacier, for instance, resembled a massive wedge of ice in 1928, but in 2021, a few tiny specs of white were all that remained on the lush green mountainside.
Because the images used for the reconstruction were taken in different years, the study used the mean year 1931 as a reference and reconstructed the surface topography of all glaciers for that year.
In their statement, the researchers stressed that glaciers did not continuously recede over the past century, pointing out that there was even sporadic mass glacier growth in the 1920s and 1980s.
But while there may have been expansion over short-term periods, Daniel Farinotti, a glaciology professor at ETH Zurich and WSL and co-author of the study, said it was "important to keep the big picture in mind".
"Our comparison between the years 1931 and 2016 clearly shows that there was significant glacial retreat during this period", and that total glacier volume is decreasing at an ever faster rate, he said.
While Swiss glaciers lost half their volume in the 85 years leading up to 2016, the monitoring network Glamos indicates that they lost another 12 per cent in the next six years alone.
Mr Farinotti said the evidence was clear: "Glacier retreat is accelerating."