KATHMANDU, Nov 3: Failure to limit global warming to 1.5 degrees Celsius could trigger extensive and potentially irreversible damage to glaciers, ice sheets, seasonal snow and frozen ground, threatening water security, mountain communities and ecosystems for centuries, according to a major new scientific report released on Monday.
The findings carry particular significance for the Hindu Kush Himalaya, including Nepal, where millions of people depend on glaciers and seasonal snow for water, agriculture, hydropower and livelihoods.
The report, Overshoot and the Cryosphere: Averting Global Meltdown, published by the International Cryosphere Climate Initiative (ICCI) in coordination with the United Nations Environment Programme (UNEP), warns that even if global temperatures eventually return to 1.5°C after temporarily exceeding the threshold, many consequences of melting ice and thawing frozen ground will persist for generations.
Drawing on research by more than 80 polar and mountain scientists, the report examines how the Earth's frozen regions will respond as temperatures exceed 1.5°C, reach their peak and subsequently decline. It concludes that the scale and duration of the overshoot will determine how much damage becomes irreversible. The authors also suggest that a genuinely safer long-term temperature target for the cryosphere could be closer to 1°C or even lower.
Mountain glaciers face substantial losses
The report warns that mountain glaciers will continue to shrink in the coming decades, even under ambitious emissions-reduction efforts, because most are already out of balance with the present climate.
Under current government policies, global temperatures are projected to reach approximately 2.8°C above pre-industrial levels by 2100. If such warming is sustained over centuries, only around 25 percent of today's global glacier ice is projected to remain.
By contrast, limiting warming to 1.5°C could preserve approximately 54 percent of existing global glacier ice, nearly twice the amount expected under current policies.
The consequences would be particularly severe in the Himalayas. If global temperatures approach 3°C, the Central and Eastern Himalaya could retain only around 10 percent of their present glacier mass once glaciers adjust fully to the warmer climate. Under a 1.5°C pathway, the corresponding figure could be around 35 percent.
Sichuan Air’s aircraft in air for an hour after overshooting th...
The Western Himalaya, Hindu Kush and Karakoram regions would also face significant losses. Around 60 percent of their glacier mass could remain under a 2°C warming scenario, compared with approximately 85 percent under a 1.5°C pathway.
The projections underline the importance of limiting warming rather than assuming that glaciers will recover once temperatures decline. Retreating glaciers can also destabilise mountain slopes, create new glacial lakes and increase the risks of glacial lake outburst floods, ice and rock avalanches and landslides. Such hazards threaten settlements, roads, bridges and hydropower infrastructure, with consequences extending far downstream.
Water security at risk
The effects of glacier and snow loss extend well beyond mountain regions. Glaciers and seasonal snow provide essential water supplies to communities, agriculture, industries and ecosystems across major river basins.
Warming will reduce seasonal snowfall, shorten the duration of snow cover and increase mid-winter melting. In many mountain regions, a growing share of precipitation will fall as rain rather than snow, changing the timing and availability of water.
These shifts could affect irrigation, hydropower generation, agricultural production and tourism. They also pose challenges for mountain communities whose cultural practices and livelihoods depend on snow and glaciers. The report points to disruptions in the traditional migration routes, timing and grazing practices of yak herders in Nepal and India as an example.
Even if temperatures decline sufficiently for some glaciers to begin regrowing, recovery could take decades to centuries. During this period, downstream communities may experience a temporary decline in glacier runoff. Water-management systems and infrastructure designed around historical river-flow patterns could therefore become less reliable.
Nepal's August disaster highlights mountain risks
The report refers to the devastating mountain disaster along the Nepal-China border in August 2026 as an example of the growing hazards associated with cryosphere degradation.
Its discussion of permafrost thaw explains how rising temperatures can weaken frozen ground, destabilise mountain slopes and increase the likelihood of sudden collapses. The report identifies the August slope collapse in Nepal as an example of such risks and estimates that the event caused economic damage equivalent to around 10 percent of Nepal's economy.
Permafrost is ground that remains frozen for at least two consecutive years. Found in high-altitude and high-latitude regions, it helps maintain the stability of mountain terrain. As it thaws, slopes can become unstable, increasing the likelihood of landslides, slope failures and changes in local drainage systems.
The implications are serious for Nepal, where settlements, roads, hydropower projects and other infrastructure are increasingly exposed to mountain hazards.
Permafrost thaw also has consequences beyond local slope instability. It releases carbon dioxide and methane into the atmosphere, adding to greenhouse gas emissions and reinforcing global warming. The report warns that carbon released during thawing is effectively irreversible on human timescales, even if some frozen ground subsequently refreezes.
Ice-sheet melting threatens coastal communities
Beyond mountain regions, the report highlights accelerating ice loss from Greenland and Antarctica as a major driver of long-term sea-level rise.
The two ice sheets are losing mass approximately six times faster than they did in the 1990s. Their retreat is expected to continue even if global warming is eventually brought back to 1.5°C, committing the world to substantial future sea-level rise.
The report estimates that the eventual adjustment of the ice sheets to current warming could contribute approximately 2–9 metres of global sea-level rise over the long term. It also warns that the loss of polar sea ice and warming of polar oceans could disrupt ocean circulation, marine ecosystems and the global climate system.
Immediate action remains possible
Despite its stark findings, the report says the worst consequences of temperature overshoot can still be limited through immediate and substantial reductions in greenhouse gas emissions.
It calls for a rapid transition away from fossil fuels, achieving net-zero greenhouse gas emissions by around mid-century, alongside large-scale and sustained carbon removal.
One scenario examined in the report suggests that global warming could peak at approximately 1.7°C around 2040, return below 1.5°C before 2100 and potentially decline towards 1°C by 2150 if ambitious mitigation and sustained carbon removal are implemented.
The authors also call for greater investment in early-warning systems, glacier and permafrost monitoring, climate-resilient infrastructure and financial support for communities facing unavoidable losses and damages.
They argue that the cryosphere must receive greater attention in international climate negotiations, particularly under the United Nations Framework Convention on Climate Change (UNFCCC).
