Context: Soaring temperatures are leading to rapid and largely irreversible changes in the mountain ranges of the world, according to a new UNESCO report.

Background: –

• 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 March 21.

Key takeaways

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.
• Warmer temperatures are not the sole cause of glacier melting. Increased wildfires and dust storms deposit black carbon and particulates on ice, darkening surfaces and enhancing solar radiation absorption. This alters the surface energy balance, accelerating melt rates, especially in high solar radiation areas, as noted in the UNESCO report.

Accelerating Permafrost Thaw

• Permafrost is any ground that stays frozen — 0 degrees Celsius or lower — for at least two years straight. 
• Rising temperatures are melting permafrost rapidly. 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.

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.
• Some mountain ranges are experiencing an increase in rainfall over snowfall, shorter snow duration, earlier snowmelt, and a reduction in snow-covered areas.

Why is this significant?

• Mountains, which cover 33 million sq km of the Earth’s surface, are crucial for sustaining life. For instance, around 2 billion people downstream depend on mountains for freshwater resources from melting glaciers.
• “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.
• According to WGMS, melted ice of glaciers accounts for 25 to 30% of the currently observed increase in global sea levels.

Source: Indian Express