Glaciers around the world are retreating at an accelerating pace. Scientists have long tracked changes in ice volume with precision, yet the full story of the 20th century remained elusive. Recently, Swiss researchers have reconstructed how Swiss glaciers changed over the last hundred years. The takeaway is stark: the glaciers have been losing mass, shrinking to about half of their 1931 volume by 2016, with a further decline of roughly 12 percent in the six years that followed.
Switzerland has a long tradition of glacier monitoring, but early 20th‑century data were sparse. A team from ETH Zurich and the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) rebuilt the topography of all Swiss glaciers for 1931 and traced their evolution using historical imagery.
To estimate past ice mass, glaciologists employed stereophotogrammetry, a dating‑back technique in Switzerland that derives shape, position and features of objects from image pairs. This approach lets researchers translate two photographs into a three‑dimensional understanding of the surface.
The team drew on images from the TerrA archive, which covers about 86 percent of Switzerland’s glacial territory. They analyzed 21,703 photographs taken between 1916 and 1947 to reconstruct surface topography and infer ice volume changes.
“If the surface topography of a glacier is known at two moments in time, it becomes possible to calculate the difference in ice volume,” explains Erik Schytt Mannerfelt, the study’s lead author.
Significant glacial retreat
The findings reveal wide variation in how glaciers shed mass. The degree of retreat depends mainly on three factors: the elevation of the glacier, the slope of its terminus, and how much debris covers the ice. Lower, more debris‑covered glaciers tend to thin faster, while steeper, higher valleys respond differently. The study highlights that mass loss is not uniform across the landscape.
“The results show strong spatial variability in thinning, with glaciers in the northeast losing mass at about twice the rate of those in the southwest. This pattern aligns with lower median heights and gentler, debris‑covered tongues in many northeastern glaciers,” the authors note.
Glaciers did not shrink every year. While the climate of the 20th century was often unfavorable, there were periods of temporary growth in some glaciers during the 1920s and again in the 1980s. Yet the long‑term trend was decisively downward.
“Even with short‑term fluctuations, the big picture matters. The comparison between 1931 and 2016 clearly demonstrates substantial retreat over that interval,” states Daniel Farinotti, professor of glaciology and co‑author of the study.
The total glacier volume in Switzerland has been decreasing at an accelerating pace, a trend corroborated by the GLAMOS glacier monitoring network hosted by ETH Zurich. In the period from 1931 to 2016, glaciers shed about half of their volume, followed by an additional decline of around 12 percent between 2016 and 2021.
Ice rivers
The retreat is not just a regional curiosity; it serves as a vital clue to how glaciers react to a warming climate. Observing ongoing thinning and measuring historical dimensions help scientists build more reliable scenarios for future glacier behavior.
During periods of rapid temperature rise, decades of regional mass balance data are crucial for understanding glacier responses to climate shifts. This long‑term view enables better projections of future changes in ice mass and river supply.
The fastest‑melting glaciers are often found in Alaska, Iceland and the Alps, with notable changes also recorded in the Pamir Mountains, the Hindu Kush and the Himalayas.
Glaciers form when snow accumulates and gradually compacts into dense ice. With increasing thickness, pressure from overlying snow drives melting and re‑freezing processes that densify the ice and reduce its porosity.
About 10 percent of the Earth’s surface hosts glaciers today, though historical fluctuations have propelled this share up to roughly 30 percent at certain times in the geological past. Glaciers store roughly three quarters of the planet’s fresh water. The vast majority of glacial ice lies in Antarctica and Greenland, with Swiss glaciers accounting for about half of the Alpine volume.
Reference report: https://tc.copernicus.org/articles/16/3249/2022/ (attribution: Copernicus Climate Change Service)
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Environment department contact details are not provided within this article. (attribution: ETH Zurich, GLAMOS)