Alpine glaciers: nearly 150 years of measurements, and a faster retreat

2026, the second-worst year on record in Switzerland

In September 2026, even at 3,500 m, not a flake of the winter’s snow was left on Switzerland’s glaciers [1]. On the 23 glaciers where the scientists of GLAMOS, the Swiss glacier monitoring network, went up to read their stakes, the winter snow had gone everywhere, right up to the highest measuring points [2]. The figures came out on 1 October: in a single year, Switzerland lost 5.5% of its glacier ice, and almost 20% since 2021 [1, 2].

Over the hydrological year, October 2025 to September 2026, the average balance of Swiss glaciers came to -2.86 m water equivalentThe depth of the layer of water you would get by melting the ice lost and spreading it over the whole surface of the glacier. 1 m of water equivalent is slightly more than 1 m of ice., barely short of the 2022 record of -3.13 m [2]. Some glaciers thinned by 2.5 to 4 m on average, and by up to 10 m in places on their tongues, in a single summer [1]. For four large glaciers, Allalin, Clariden, the Great Aletsch and the Rhône, 2026 was even worse than 2022 [2]. The table below sets it against the last five years [2, 3, 4].

Why such a year? First, a lean winter: from November 2025 to April 2026, average snow depth ranked among the ten lowest since measurements began [1]. Then a summer with no let-up. From May to September, the freezing level stayed above 4,000 m on 76 days, more than twice the average and a record [1]. June, July and August were the hottest ever measured in Switzerland, according to MeteoSwiss, as cited by GLAMOS [2]. Stripped in places of their protective snow as early as June, the glaciers melted bare all summer.

If 2026 did not quite beat 2022 nationally, it is because the spring snowpack was slightly less depleted (25% below normal on 30 April, against 32% in 2022) and less Saharan dust, which dirties the snow and speeds up melting, settled on it [2]. Two small glaciers, Bella Tola in Valais and Griessfiren/Plattalvafirn in the canton of Glarus, did not survive the summer [1, 2].

Length, area, volume, mass balance: four measurements not to be mixed up

‘The glacier retreated by 54 m’ and ‘the glacier lost 7 m in thickness’ are not the same statement, yet they can describe the same glacier in the same year. Take the Pasterze, Austria’s largest glacier, at the foot of the Grossglockner: in 2024-2025, its snout retreated by 54 m, its tongue sank by 7.3 m on average, and the ice there now moves forward by less than 5 m a year [6]. A glacier can be measured in four ways, and each tells a different story.

• Length: the position of the snout, the end of the tongue, surveyed at the end of each summer with a tape, GPS or a drone. It responds to the climate years late, and depends heavily on the terrain.
• Area: the outline of the glacier, mapped from aerial photographs. Switzerland has drawn up several inventories, from 1850, reconstructed, to 2023 [7, 8].
• Volume: the amount of ice, calculated by comparing surveys of the terrain taken several years apart, and from thickness measurements.
• Mass balance: what the glacier gains in snow over winter, minus what it loses to melt in summer. It is measured with stakes drilled into the ice and snow cores, and expressed in metres of water equivalent [5].

In France, this painstaking work falls to the GLACIOCLIM observatory, set up in 2003 and run by the Institute of Environmental Geosciences in Grenoble, with the equivalent of two and a half full-time staff, plus students [10]. On each glacier monitored in the French Alps, 20 to 25 wooden stakes measure the melt, 5 to 10 cores measure the winter snow, and roughly every five years aerial photographs are used to check the whole picture [5].

These four quantities cannot be added together or compared with one another: a snout can stay put while the glacier thins, or retreat by 350 m, even nearly 900 m, in a year because a tongue grown too thin has broken off above a rock step. That is why our charts never mix them.

Before 1880, engravings and moraines rather than measurements

Around the middle of the 19th century, Alpine glaciers reached their last great extent, at the end of the Little Ice AgeA colder period, several centuries long, during which Alpine glaciers were far larger than today; it ended around the middle of the 19th century.. Nobody was yet measuring them regularly. What we know of their size comes from reconstructions: engravings, paintings, old maps, travellers’ accounts, then the first photographs, and the morainesThe ridges of stones and boulders a glacier pushes and drops along its sides and at its snout. They trace its former extent. left behind [8, 9].

These reconstructions are valuable, but they are not measurements. In the database of the World Glacier Monitoring Service (WGMS), the record of the Mer de Glace goes back to 1570, pieced together from texts, maps, drawings, engravings and, later, photographs [9]. That of the Rhône Glacier shows its snout at its furthest point down the valley in 1856, then a retreat of about 840 m up to 1879, again from old documents [9].

Regular measurements followed: snout positions have been surveyed every September since 1870 at the Mer de Glace and the Argentière Glacier [10], and systematically in Switzerland since 1880 [7]. In Austria, the Alpine Club’s glacier survey service has 135 years of history [6]. In 1894, an International Glacier Commission, set up on the initiative of the Swiss scientist François-Alphonse Forel, launched the worldwide coordination that the WGMS carries on today [11]. Mass balance came later: from 1914 in Switzerland [2], then 1949 at Sarennes and 1957 at Saint-Sorlin in France, and 1953 at Hintereisferner in Austria [9].

Since 1850, how many kilometres of retreat?

To answer that, you need long, unbroken records. The Swiss network has several, and we took four of them, among the glaciers walkers know best, from the measurement file published by GLAMOS [8]. Each line starts at zero at the beginning of its record; the Rhône starts from its reconstructed maximum of 1856.

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The Great Aletsch Glacier, the largest in the Alps, has retreated 3.2 km since 1892, and the Morteratsch, in the Engadine, 2.8 km since 1894. The Rhône Glacier has lost 1.8 km since 1879, on top of the 840 m reconstructed for the two previous decades. The Trient Glacier, above the village on the Tour du Mont-Blanc, has retreated 1.4 km since 1879 [8]. And the pace is not slackening: since 2000, the Morteratsch has lost a little over 1 km, the Aletsch nearly 1 km, the Trient 750 m and the Rhône 650 m [8].

Yet the records hold a surprise: the Trient has also advanced, twice. From 1879 to 1896, its snout gained about 180 m; then, from 1957 to 1987, about 390 m [8]. Glaciers with a steep tongue can advance during short runs of good years, Swiss glaciologists explain, whereas large glaciers with a long, gently sloping tongue, such as the Aletsch, retreat steadily [7]. In France, the Argentière Glacier also advanced by nearly 400 m between 1970 and 1990, after a run of cool summers and snowy winters [5].

Since then, the trend has been unambiguous. In 2024, 66 of the 69 Swiss glaciers surveyed retreated, by 1 to 64 m for nine out of ten [7]. In Austria, the glaciers surveyed in both 2024 and 2025 shortened by 20.3 m on average in a year, the eighth-largest retreat in 135 years of measurements, and 94 of the 96 glaciers observed retreated [6].

Mass balance, or what a glacier really loses each year

Mass balance follows the climate of the year: it is the result of the snow that fell in winter and the melt of summer [5], whereas length responds years later and depends on the terrain [7]. Each spring, glaciologists core the winter snow; each summer, they read stakes drilled about 10 m into the ice, two to four times a season in the French Alps [5]. We added up these balances for three glaciers in three countries, monitored without a break since 1957, using the WGMS database [9].

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All three lines tell the same story. Until the mid-1980s, they barely dip: in France, glaciers even grew between 1954 and 1981, thanks to cool summers followed by wet winters [5]. Then they plunge. Since 1957, the Saint-Sorlin Glacier, in the Grandes Rousses, has lost the equivalent of a 69 m layer of water across its whole surface; Hintereisferner, in the Ötztal Alps, 52 m; Silvretta, in the Grisons, 38 m [9]. In all three records, 2022 remains the worst year [9].

The slope of the lines shows the speed. By our calculations from the WGMS data, Saint-Sorlin lost an average of 0.1 m of water equivalent a year between 1957 and 1985, and 2.1 m a year since 2001, about twenty times as much. Hintereisferner has gone from 0.3 to 1.3 m a year, and Silvretta, in balance until the mid-1980s, now loses 1.2 m a year [9].

Other records say the same. The five glaciers monitored in France, four in the Alps and one in the Pyrenees, have lost an average of 39 m of water equivalent since 2001 [5]. The twelve Austrian balances available for 2024-2025 average -1.72 m of water equivalent [6]. And worldwide, the WGMS reference glaciers have lost more than 25 m of water equivalent on average since 1980 [12].

How much ice is left in Switzerland?

To work out the total volume, Swiss glaciologists measured ice thickness by radar and modelled it across all the country’s glaciers; the annual balances then make it possible to track that stock year by year [2]. At the end of 2026, Switzerland still had about 42.6 km³ of ice, more than 30 km³ less than in 2000, and its glaciers covered about 714 km², a third less than in 2000 [2]. The loss is speeding up, decade by decade [2].

This melting ice feeds the rivers in summer, but the contribution is shrinking: with 2.5 km³ of ice lost, 2026 comes only third in recent decades and supplied less water than 2003, because there is less ice left to melt. According to GLAMOS, peak meltwater has probably passed [2].

Small glaciers, meanwhile, simply vanish. More than 1,000 Swiss glaciers disappeared between 1973 and 2016 [2], then 159 between the 2016 and 2023 inventories, or 11%; in Ticino, almost 40% in six years [7]. The 2023 inventory still lists 1,299 [7].

Will the glaciers of the Alps disappear? What the projections say

A projection is not a forecast: it describes what would happen under a given greenhouse gas emissions scenario. In 2019, a study simulated the future of every glacier in the Alps using the IPCC scenarios [13]. Whatever the scenario, they would lose 47 to 52% of their 2017 volume by 2050. After that, everything depends on emissions: with steep cuts (the RCP2.6 scenario), about a third of the 2017 volume would remain in 2100; with emissions that keep rising (RCP8.5), the glaciers would have largely disappeared by 2100, with 94% of their volume lost [13]. That study was published before the summers of 2022 to 2026.

A study published in December 2025 counts instead the glaciers that vanish, for warming of 1.5 °C to 4 °C by 2100 compared with pre-industrial times [14]. In the Alps, where small glaciers dominate, more than half would disappear within the next twenty years, a timeline that depends little on the scenario; with 4 °C, about twenty would remain in 2100 in the study’s ‘Central Europe’ region, that of the Alps, 99% fewer than today [14].

Moraines, ladders, rerouted paths: what changes for walkers

Where the ice retreats, it leaves a new and unstable landscape: steep moraine slopes, scree, meltwater lakes, and dead ice buried under the stones. The German Alpine Club sums it up in its research programme on the Eastern Alps: steep moraines are unstable and prone to rockfall, rock faces freed by the ice to rock avalanches, and dead ice can cause unpredictable subsidence. Routes have to be adapted year after year, or abandoned [15].

Around the Mer de Glace, a study traced the approaches to five mountain huts over more than a century: largely unchanged for most of the 20th century, these paths have been altered many times since the 1990s, because of the thinning glacier and the erosion of the moraines. In 2017, they included 633 m of ladders, and the danger they pose continues to rise, the authors note [16]. At Montenvers, a new gondola opened in February 2024 a few metres from the glacier, cutting the walk for visitors heading down to the ice cave [17].

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Elsewhere, the examples are there in the official reports. On the Dachstein, in Austria, rockfall from the faces of the Mitterspitz increased so much, with the retreat of the glacier and changes in the permafrost, that the normal route from the Adamek hut had to be moved in 2024; the Austrian Alpine Club also reports routes that have become harder to follow [6]. In Switzerland, cavities carved under glacier tongues collapse and leave deep craters, as on the Rhône Glacier [1, 2].

What this means for you, on a waymarked path: an old guidebook may describe an approach that no longer exists, and a moraine that looks solid may give way underfoot. The Swiss Alpine Club’s scale mentions sections on glaciers from grade T4 upwards; we explain it in our guide to route grades.

Going to see the glaciers, with the figures in mind

No need to set foot on the ice to see these glaciers. A valley path, a rack railway or a road pass is often enough to read in the landscape what the records say: the grey tongue below, the smooth rock it has polished, and the long crests of moraine. Many of these places can be reached by train and bus, and a night in a mountain hut lets you see them in the evening light, then again in the morning.

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The moraines lining Alpine glaciers often trace their extent in 1850: the Swiss inventory of 1850 relies partly on them, and on old maps [8]. The smart move, next time a path takes you along one of those ridges of stones: look up at the ice, far above, and gauge the distance. You will have a century and a half of data under your boots.

Guillaume Hoarau

Camping, wild camping, bushcraft and hiking

Guillaume Hoarau writes for Outfarer about camping, wild camping, bushcraft and hiking. A survival-skills enthusiast and a collector of old field manuals, he likes clear explanations, lists that earn their place and other people’s stories, which he tells well.

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