Earth’s 275,000 glaciers currently store around 70 per cent of the world’s freshwater and are relied on by almost two billion people.
But to mark World Glacier Day on Friday, scientists now warn that glaciers in many parts of the world ‘will not survive the 21st century’.
A report from the World Meteorological Organization (WMO) found that five of the last six years have seen the fastest glacier retreat on record.
As this melting releases vast quantities of water, experts warn that 10 million people around the world are now at risk of devastating glacial floods.
Since records began in 1975, glaciers have lost more than 9,000 billion tonnes of mass – equivalent to a layer of ice as big as Germany and 15 miles (25km) thick.
While this loss has been moderate in areas such as the Canadian Arctic or Greenland, some areas have been hit significantly harder.
In Europe’s Alps and Pyrenees, glaciers lost 40 per cent of their mass between 2000 and 2023 alone.
WMO Secretary-General Celeste Saulo says: ‘Preservation of glaciers is a not just an environmental, economic and societal necessity. It’s a matter of survival.’
Glaciers store 70 per cent of the Earth’s freshwater, but scientists now warn that many glaciers won’t survive the 21st century. Pictured: The Rhone Glacier, Switzerland above a lake formed by glacial meltwater
As the climate warms due to human-caused climate change, the natural cycle of melting and recovery which has kept glaciers stable for thousands of years is failing. In Greenland, satellite evidence clearly shows how the glaciers have darkened and shrunk between 1973 (left) and 2022 (right)
Naturally, glaciers shrink during the warm summer months and grow larger with compacted snow which falls over the winter.
This process has kept Earth’s current glaciers stable throughout the seasons for tens or hundreds of thousands of years.
However, since humans began introducing large amounts of CO2 and other greenhouse gases into the atmosphere, this balance has now been disturbed.
A warming climate, which scientists have conclusively linked to human activity, means that glaciers melt faster in the summer and recover slower in the winter.
During 2024, the world’s glaciers lost 450 billion tonnes of mass as they shrank – the fourth-worst year on record.
In that same period, glaciers in Scandinavia, Svalbard and North Asia saw their greatest annual loss on record.
According to the WMO’s research, the period between 2022 and 2024 was the largest three-year loss of glacier mass ever recorded.
A recent study found that glaciers are now retreating so fast that they release an average of 273 billion tonnes of water every year, or 6,542 billion tons between 2000 and 2023.
Five of the last six years have seen the fastest glacier loss on record. In 2024 alone, the world’s glaciers lost 450 billion tonnes of mass
A recent study found that glaciers are now retreating so fast that they release an average of 273 billion tonnes of water every year, or 6,542 billion tons between 2000 and 2023. Pictured: the Argentiere glacier in France which has retreated more than a kilometre since 1990
Ms Saulo adds: ‘Seven of the ten most negative mass balance years have occurred since 2016.’
If this continues, the WMO now believes that the ‘eternal ice’ at the core of many glaciers will not last beyond 2100.
Sulagna Mishra, a scientific officer at the WMO, says that scientists are now seeing an ‘unprecedented change in the glaciers’, which could be irreversible.
Ms Mishra adds: ‘[If] the temperatures are rising at the rate they are at the moment, by the end of 2100, we are going to lose 80 per cent of the small glaciers.’
In the short term, the enormous quantities of meltwater released by glacial retreat are creating a severe risk of flooding.
Writing in The Conversation, Professor Suzanne O’Connell, of Wesleyan University, and Dr Alton Byers, of the University of Colorado Boulder, argue that 10 million people are now in danger.
The scientists explain that, as glaciers melt, the water drains into depressions once occupied by the glacier, forming huge lakes.
Many of these lakes are only held in place by fragile natural dams made of rock and ice which were deposited by the glacier over centuries.
Scientists warn that rapid melting increases the risk of glacial lake outbursts. Melting water builds up in large depressions left behind by the retreating glacier. If this water escapes, it produces a flood which will destroy everything in its path
A recent study has found that the glacial lakes around the world are growing faster due to climate change. In total, glacial lakes now store more than 160 gigatonnes of water
They write: ‘Too much water behind these dams or a landslide into the lake can break the dam, sending huge volumes of water and debris sweeping down the mountain valleys, wiping out everything in the way.
‘That dangerous mix can rush downstream at speeds of 20-60 mph (30-100 kph), destroying homes and anything else in its path.’
The casualties caused by such an event can be extreme, due to the sudden and violent nature of the flood.
In 2023, a glacial lake outburst in the Himalayas damaged more than 30 bridges, destroyed a hydroelectric power plant and killed over 50 people.
In the most deadly example, in 1941 a wave caused by an avalanche that fell into Laguna Palcacocha, a glacial lake in the Peruvian Andes, broke the dam that had contained the lake for more than a decade.
The subsequent flood rushed down the valley to the city of Huaraz, killing between 1,800 and 5,000 people.
Recent studies have shown that the risk of glacial lake outbursts has only become greater as the ice melts faster.
Laguna Palcacocha is now 14 times as big as it was in 1941 and Huaraz is now home to 120,000 people.
In 1941 a wave caused by an avalanche that fell into Laguna Palcacocha (picture), a glacial lake in the Peruvian Andes, broke the dam that had contained the lake for more than a decade. The subsequent flood rushed down the valley to the city of Huaraz, killing between 1,800 and 5,000 people
Modelling studies estimate that a glacial flood today could threaten the lives of 35,000 people.
Similarly, meltwater can build up inside massive systems of ice caves within glaciers before being suddenly released in an event called an ‘englacial conduit flood’.
Glacial retreat can also cause flooding risks for people living nowhere near the ice itself.
As glaciers melt, they deposit vast amounts of freshwater which had been stored on land into the sea, causing sea levels to rise.
Scientists estimate that glacial meltwater is now the second biggest contributor to sea level increases, raising sea levels by 0.7-inch (18mm) between 2000 and 2023.
Professor Michael Zemp, director of the World Glacier Monitoring Service, told UN News: ‘This might not sound much, but it has a big impact: every millimeter sea-level rise exposes an additional 200,000 to 300,000 people to annual flooding.
However, in the long term, the concern is that rapidly retreating glaciers will leave hundreds of millions without access to fresh drinking water.
In the two decades from 2000 to 2023, the world’s glaciers lost the amount of water consumed by the entire global population over 30 years.
A long-term concern is that the disappearance of the world’s glaciers will leave alpine communities with no source of freshwater. Current estimates suggest that two billion people currently rely on glaciers as their main source of drinking water. Pictured: A gorge near the Oberaletsch Glacier, Switzerland that was once filled with ice
This freshwater is essential to the livelihoods and survival of many people, especially in hot or high-altitude areas.
If those glaciers were to vanish as the WMO predicts, millions would be forced to find alternative water sources or migrate elsewhere.
Current estimates suggest that 1.9 billion people – 22 per cent of the world’s population – live downstream of glaciers and rely on them as their main source of drinking water.
As the UN marks the first-ever World Glacier Day on Friday, scientists and UN officials are calling for more to be done to protect these valuable resources.
Professor Zemp says: ‘If I think of my children, I am living in a world with maybe no glaciers. That’s actually quite alarming.’
