On the rocks

In 1840, a man named Friedrich Simony, then in his late 20s, travelled to Dachstein in the Austrian Alps to study the mountains. Over the next 50 years, the geographer would return again and again to the region: Mapping its mighty elevations, measuring its lakes and, perhaps most importantly, snapping its glaciers. 

It is through his photographs that, for the first time, Simony was able to see something that now seems sadly commonplace. The glaciers were disappearing. These images provided the first scientific evidence that the Dachstein-Hallstätter Glacier was gradually getting smaller. Today, scientists estimate that because of the rapid rise in global temperatures, the Dachstein-Hallstätter Glacier, which has occupied the Alps for thousands of years, will disappear by the end of the century. 

What Simony, now known as the father of glaciology, saw over his career wasn’t just the shape of things to come, it was the beginning of the end of the glacier. Today you don’t need to compare photographs like Simony did to take in the scale of the loss. Many glaciers now have milestones marking where they once extended to, often a dramatic distance from where they terminate today. 

A recent paper in the journal Science noted that if present climate polices continue, less than a quarter of glacier mass will remain by the end of the century. That estimate assumes a 2.7°C warming. The paper notes that though there will be significant glacial loss, much can still be preserved if warming is kept to the magic 1.5°C level set in the Paris Agreement. 

The (last) Year of the Glacier? 

In recognizing this slow-moving catastrophe, the United Nations declared 2025 the International Year of Glaciers Preservation. 

At a January 2025 event introducing the year, Stefan Uhlenbrook, Director of Hydrology, Water and Cryosphere at the World Meteorological Organization (WMO), said, “We got the question, ‘why do we need another year, there are so many of these years and why do we need one on glaciers preservation?’” He then showed audience a data set showing how glacier mass had changed over the past 50 years. The bluer the bar, the more glacier mass had increased in a given year; the more red, the more mass a glacier had lost. As the chart approached the present day, the deeper red it became. 

“In the Swiss glaciers, they lost about 10 percent of their volume in only two years, so the situation is really dramatic,” Uhlenbrook said. 

Much is at stake when glaciers melt away. They hold about 70 percent of the world’s freshwater. Remove just a little of that amount and you have water scarcity, rising sea levels and an increased risk of floods and landslides, not to mention all the ecosystems and human livelihood (such as agriculture) that depend on that water supply. The faster glaciers melt, the more sea levels rise. Currently, oceans rise by about 4 millimeters a year – of which one full millimeter comes from glaciers. 

Glacier retreat is damaging in other ways. The frozen ice of a glacier is a kind of archive, one which traps dust, atmospheric particulates and even tiny bubbles of prehistoric air. Scientists take a core sampling of the ice, which sometimes is 100,000 years old, to understand what the atmosphere and climate was like long before humans were able to record it. These ice cores give us some insight into both the past and future; if the glaciers melt away the only remaining record of this knowledge could be efforts like the Ice Memory Sanctuary. This facility is currently being built in Antarctica by the Ice Memory Foundation, a scientific initiative, to house a collection of irreplaceable ice cores for future generations to research, much the same way that the Svalbard Global Seed Vault in Norway provides humanity a backup of the world’s crops. 

“The sight was Dantesque” 

Glacier retreat is most catastrophic for communities in developing countries living beneath them. But it is dramatic for wealthy countries too. In May, just three months after the UN kicked off the Year of the Glacier, the Birch Glacier in the Swiss Alps began to crack. A massive rockfall from the mountain on which it sits finally caused it to give way sending millions of cubic meters of debris down towards the village of Blatten. 

In just a few seconds, rock and ice completely buried Blatten, destroying houses that had stood for centuries and, quite literally, wiped the town from the map. Before and after photos hardly seem like they were taken from the same place; only a few buildings and roads remained untouched. 

For all the destruction the Swiss glacier caused, only one death was recorded, a local shepherd who was outside the evacuation zone. The rest of the town of about 300 had fled to safety when it became clear that the Birch Glacier may not be entirely stable. Places without early warning systems, evacuation procedures or adequate protective infrastructure rarely fare as well. 

A melting glacier is not like an ice cube melting on the ground, which expands evenly. Glaciers often hold back huge amounts of water and rock, so when they lose structural integrity they can quickly cause problems many miles away. For example, glacier lakes are a common, and picturesque, sight in the mountains. Yet like a bathtub slowly filling with water until it spills over, global warming and glacier melt create an ever-increasing risk that these lakes will spill over onto nearby communities. According to a 2023 estimate, 15 million people worldwide are at risk from these glacial lake “outburst” floods. 

“The changes we are making to our planet are increasing our collective risk,” said Jenty Kirsch-Wood, Head of Global Risk Management and Reporting at the United Nations Office for Disaster Risk Reduction. “As that risk is increasing, it is essential that we invest in better hazard monitoring.” 

Monitoring every glacier in every country is an expensive endeavor and history is filled with stories of how quickly things can go wrong if there is no way to tell if danger is on its way, whether it is a slow drip or a force majeure. 

In 1941, a block of ice broke off from Peru’s Palcaraju mountain and fell into Lake Palcacocha. The resulting outburst flood killed at least 1,800 people and destroyed a third of the city of Huaraz. It only took the water 15 minutes from the initial crack of ice until the water reached the city. 

“The black water did not slide, but formed huge, inarticulate, boiling waves. Dense dust covered the scene. The sight was Dantesque,” a survivor later told an author researching the incident. “When I turned my face, my mother had disappeared.”