7

Mountain glacier loss is accelerating

Key messages

  • Mountain glaciers respond to changes in atmospheric forcing over shorter temporal scales than ice sheets, and have caused almost one quarter of sea-level rise so far.
  • Glacial melting puts the growing populations living downstream at risk of flash-floods and water shortages.
  • As these glaciers retreat, biodiversity in high-alpine catchments may strongly decrease, compromising ecosystem functions.

Insight explained

Mountain glaciers are highly sensitive indicators of climate change. Improved satellite observations and modelling have enhanced our ability to measure the response of glaciers to climate change and project their evolution, while Indigenous and local knowledge have extended the time depth and spatial resolution of our understanding. In comparison with the vast ice sheets in Greenland and Antarctica, mountain glaciers occupy much smaller areas and account for a sea-level rise potential of only about 30 cm. However, since mountain glaciers are melting much faster than ice sheets, their mass loss explains almost one quarter of current sea-level rise. Glaciers contribute to healthy mountain environments. During dry periods, glacier meltwater is vital for maintaining river flows that support mountain and downstream regions, recharging aquifers, providing freshwater for human consumption and irrigation, and sustaining ecosystems and biodiversity, as well as fisheries and shipping. Additionally, glaciers have considerable spiritual, cultural and touristic value.

Present-day observations of glacier change reveal a loss of 267±16 Gt yr-1 with a clear acceleration over the last two decades. Globally, glacial mass loss is potentially around 12% greater than previously reported, due to ice melt occurring below the water surface that is unaccounted for by available estimates. As these glaciers retreat, high-alpine catchments may lose species and ecosystem function.

New global glacier projections estimate that glaciers will lose between 26% (at +1.5°C) and 41% (at +4°C) of their current volume by 2100 (Figure 7). Relative mass loss varies greatly at regional scales, with mid-latitude regions such as Western Canada, Central Europe and Caucasus expected to experience widespread deglaciation if warming goes beyond 3°C. Limiting the temperature increase by reducing GHG emissions is thus critical for preserving these glacial regions and limiting their contribution to sea-level rise.

The impact of climate change on mountain environments is diverse. Glacier loss poses immediate flooding risks to the surrounding communities, and when compounded by the thawing of permafrost, it causes cascading hazards such as landslides and debris flows. Glacier loss also poses medium-term risks of water shortages, including areas with very large populations in the Hindu-Kush Himalayas. In all cases, additional in situ observations are key and will help reduce uncertainties in glacier change projections. Improving these projections will benefit from incorporating high-resolution models to ensure projections are provided at the correct scale for disaster risk management, and implementing programmes that build trust and collaboration between governments and Indigenous and local peoples to ensure the success of adaptation measures.

IN FOCUS

More people than ever live in the watersheds of the highest mountains


Increasingly large numbers of people are affected by mountain glacier loss. Mountainous regions with high population densities, such as the Himalayas, are particularly vulnerable (Figure 7). Approximately 2 billion people downstream of the Himalayas currently rely on mountain water sources, compared with 0.6 billion in the 1960s. Central Asia, South Asia and tropical and subtropical western South America are predicted to experience the most significant impacts from changing water availability this century. Variable timings of glacier and snow melt affect water availability and may lead to conflict over resources. Downstream mountain populations are also growing. Today, there are roughly 15 million people worldwide exposed to glacial lake outburst floods. Rapid GHG emissions reductions will offset the worst of these impacts. However, effective community-driven adaptation strategies will be key in supporting resource and disaster risk management, especially for vulnerable communities.

Implications & Recommendations

Adaptation strategies would benefit from more stakeholder cooperation to ensure effective implementation and management. The agreement at COP27 to establish a Loss and Damage Fund highlights the need for disaster risk reduction and more support for vulnerable populations. Still, too few risk control measures have been implemented to address the impacts of global climate change in mountain regions.

In order to prioritise comprehensive climate adaptation policies for immediate- and medium-term challenges, climate negotiators and decision-makers at all levels should:

  • Invest in climate-resilient and adaptable infrastructure, and urban planning considering rapid- and slow-onset challenges (e.g. glacial flooding, freshwater scarcity).
  • Enhance early warning systems and emergency preparedness in vulnerable communities for glacial flooding.
  • Prioritise water resource management, investing in water-efficient technologies, promotion of sustainable land management practices, and diversifying water sources whenever possible.
  • Develop robust procedures for assessing and consulting on the possibility of relocation of vulnerable communities from high glacial melt flood risk zones (always through participatory processes with the affected communities, see Insight 8).
  • Safeguard and restore wetlands, mangroves and other ecosystems that help to mitigate the impacts of glacial loss, reducing the risks of flooding and erosion.
  • Foster collaborative efforts between researchers, governments and local communities among wealthier and poorer parts of the world, which are crucial for filling data gaps and improving modelling accuracy.
  • Seek regional collaborations for effective resource allocation and risk reduction.
  • Support glacier protection laws, which have emerged in the last decade.
Figure 7. Glacier loss and sea-level rise from 2015–2100. Discs show global and regional projections of glacier mass remaining by 2100 (relative to 2015) for global mean temperature change scenarios. The size of each disc is based on the region’s contribution to global mean sea-level rise from 2015–2100 for the +2°C scenario. Nested rings are coloured by temperature change scenarios showing normalised mass remaining in 2100. Regional sea-level rise contributions larger than 1 mm sea-level equivalent for the +2°C scenario are in the centre of each disc. The colour of the outer circle refers to the risk to livelihoods and the economy from changing mountain water resources, for global warming between 1.5–2°C (IPCC, 2022, AR6-WG2:CCP5.3). The map shows population density (people per km2) in grey, and glaciers in blue. Modified from: Rounce et al. (2023). Global glacier change in the 21st century: Every increase in temperature matters. Science, 379(6627), 78–83. doi: 10.1126/science.abo1324

Where do we stand?

Earth system

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What to do?

Solutions and Barriers

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Year

1

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2

A rapid and managed fossil fuel phase-out is required to stay within the Paris Agreement target range

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3

Robust policies are critical to attain the scale needed for effective carbon dioxide removal (CDR)

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4

Over-reliance on natural carbon sinks is a risky strategy: their future contribution is uncertain

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5

Joint governance is necessary to address the interlinked climate and biodiversity emergencies

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6

Compound events amplify climate risks and increase their uncertainty

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7

Mountain glacier loss is accelerating

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8

Human immobility in areas exposed to climate risks is increasing

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9

New tools to operationalise justice enable more effective climate adaptation

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10

Reforming food systems contributes to just climate action

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