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Soaring temperatures are leading to rapid and largely irreversible changes in the mountain ranges of the world, according to a new UNESCO report. In several regions, higher elevations seem to be warming faster than lower ones; glaciers are melting at an accelerated rate; permafrost is thawing at an increased rate; snow cover has declined; and snowfall patterns have become more erratic.
The ‘The United Nations World Water Development Report 2025 – Mountains and glaciers: Water towers’ was released to mark the first-ever World Day for Glaciers on Friday (March 21).
Here is a look at how rising temperatures impact mountain ranges, and why this is significant.
What is happening?
GLACIER MELTING: Glaciers are disappearing faster than ever, with the last three-year period seeing the largest glacial mass loss on record. Scientists measure the state of a glacier by measuring how much snow falls on it and how much melt occurs every year, according to the World Glacier Monitoring Service (WGMS).
Since 1975, glaciers, which do not include the Greenland and Antarctica ice sheets, have lost more than 9,000 billion tonnes of mass. “This is equivalent to a huge ice block of the size of
Germany with a thickness of 25 metres,” Michael Zemp, director of the Switzerland-based World Glacier Monitoring Service, said during a press conference on Friday.
He also noted that five of the last six years registered the largest losses, with glaciers losing 450 gigatons of mass in 2024 alone. Last year, glaciers in Scandinavia, the Norwegian archipelago of Svalbard and North Asia witnessed the largest annual loss of overall mass on record.
Warmer temperatures are not the only reason behind accelerating glacier melting. More frequent and intense wildfires and dust storms are leading to more deposition of black carbon and other particulate matter on glacier surfaces and perennial snowpacks. “The impurities darken snow and ice surfaces, thus causing greater absorption of solar radiation… This can significantly influence the surface energy balance, thereby increasing melt rates, especially during periods and at locations of high incoming solar radiation,” according to the UNESCO report.
ACCELERATING PERMAFROST THAW: Permafrost is any ground that stays frozen — 0 degrees Celsius or lower — for at least two years straight. In high-altitude regions, permafrost can underlie much of the landscape. However, rising temperatures are melting permafrost in these regions rapidly. This is an issue as permafrost contains a vast amount of organic carbon and other nutrients. Mountain soils with permafrost contain approximately 4.5% of the global soil organic carbon, according to the UNESCO report. As the permafrost thaws, this organic carbon is released into the atmosphere, exacerbating climate change.
Moreover, permafrost in mountain regions also stabilises rock slopes, moraines (material left behind by a moving glacier), and debris-covered slopes. However, due to permafrost melting, slopes become more vulnerable to erosion, increasing the risk of landslides and other hazards.
DECLINE IN SNOW COVER: According to the UNESCO report, snow cover in nearly all mountain regions has reduced, especially in spring and summer, with an expected further decrease in the coming decades. Snow cover is the total of all the snow and ice on the ground. It includes new snow and previous snow and ice that have not melted.
A study, ‘Uneven global retreat of persistent mountain snow cover alongside mountain warming from ERA5-land, published in the journal Nature in November 2024 revealed that there had been a significant global mean decline of 7.79% in persistent snow cover between 1979 and 2022.
ERRATIC SNOWFALL PATTERNS: In some regions, the elevation at which rainfall transitions to snowfall is shifting upwards due to atmospheric warming, the UNESCO report says. “Lower elevations and warmer climates are therefore undergoing greater decreases in snow cover depth and duration,” the report added.
It has also been observed that some of the mountain ranges are receiving a greater fraction of precipitation falling as rain rather than snow. The snow duration has reduced, snow-melt is taking place earlier than usual, and the snow-covered area has shrunk.
Why is this significant?
Mountains, which cover 33 million sq km of the Earth’s surface, are crucial for sustaining life on the planet. For instance, around 2 billion people downstream depend on mountains for freshwater resources from melting glaciers. If climate change-induced glacier melting continues at the current rate, it can have catastrophic impacts on these people.
“Water flows from mountains will become more erratic, uncertain and variable. Changes in the timing and volume of peak and low flow periods, increased erosion and sediment loads will affect water resources downstream, in terms of quantity, timing and quality,” the UNESCO report said.
Glacier melting and permafrost thaw also increase the risk of glacial lake outburst floods (GLOFs). GLOFs are sudden and catastrophic floods caused by the failure of natural dams, usually formed by glacial moraines or ice, which contain glacial lakes. The report noted that these floods “alone have resulted in more than 12,000 deaths in the past 200 years, and have caused severe damage to farmland, homes, bridges, roads, hydropower plants… often prompting further internal displacement”.
According to WGMS, melted ice of glaciers accounts for 25 to 30% of the currently observed increase in global sea levels. Between 2006 and 2016, the global mass loss of glacier ice amounted to 335 billion tonnes of lost ice per year, which corresponded to an increase in sea levels of almost 1 mm per year. Every millimetre can expose up to 300,000 people to annual flooding, WGMS said.
“When you ask me how many people are actually impacted, it’s really everyone… It is really high time that we create awareness, and we change our policies and… We mobilise resources to make sure that we have good policy frameworks in place,” Sulagna Mishra, a scientific officer at the World Meteorological Organization, said in a press statement.
