When mountain comes melting

Earth's climate is undergoing radical changes in response to continued emissions of greenhouse gases, such as carbon dioxide, and land use changes, such as deforestation. Sixteen of the warmest years on record have all occurred in the last 17 years, and 2016 was the warmest of all. That year, atmospheric carbon dioxide concentrations reached 400 ppm (parts per million) for the first time in at least a million years.

The impact of climate change is currently seen globally in sea level rise, increased flooding and storms, and in changes to ecosystems. Future changes have the potential to affect human societies by destabilising economies, upsetting political and social relationships, and changing the context within which countries develop and relate to their neighbours and the wider international community.

One of the anticipated outcomes of global warming is the melting of mountain glaciers, and this is underway in almost all mountain regions. In much of central Asia and South America, glaciers behave as water towers by providing a continuous supply of freshwater to the lowlands and thereby allowing economic activities. Their recession over the past few decades in response to climate change is striking. This will impact water supplies to vulnerable communities across the globe, create and increase mountain hazards and affect economic development in mountain regions.

Dangers of glacier recession

Mountain glaciers provide the resource base upon which social and economic development in mountain regions is dependent. Seasonal melting of frozen water stores, such as glaciers and snowpacks, smoothes the effect of highly variable summer rainfall, and glaciers play a crucial role in supporting ecological, social and economic systems in the mountains and downstream. This is particularly important in the Hindu Kush-Himalaya (HKH), home to the largest area of glacial ice outside of the Poles and which produces water for around 40 per cent of the world's population, including large areas of India, Pakistan, Afghanistan and China. However, these hydrological resources are highly sensitive to climate change, and have lost around 25 per cent of their mass over the past century.

Worse, the global recession of mountain glaciers is now accelerating, with recent estimations suggesting global mass change rates of -259±28 gigatonnes per year over the past decade or so. Warming is also likely to increase most at high altitudes, which means small high mountain glaciers are likely to be highly sensitive to warming, with many ultimately disappearing. For instance, recent numerical climate model projections suggest that by 2100 glacier mass in the Himalayas may be 40-70 per cent lower than its present extent.

While glacier melting initially leads to short-term increased glacial runoff, dwindling frozen water stores are unsustainable in the long-term as this will eventually lead to decreased summer runoff. This reduced water security associated with climate change will have enormous negative impacts on mountain communities and on downstream human and natural systems.

Water supply problems also have the potential to destabilise political systems in regions where rivers are transboundary; glaciers in one state may feed rivers supplying water to the other. This is a potential major political and economic problem in many central Asian countries that rely on transnational rivers. Sustainable water resource use cannot therefore be achieved without a high level political agreement and there remains the threat of water conflicts, exacerbated by glacier melt.

Compounding hazards

One way that mountain glaciers respond to climate change and melting is by increasing their surface debris cover as rockfalls from mountain slopes deposit rock debris onto glacier surfaces. This has the effect of partially insulating glacier ice from short-term climate warming and this makes many of these debris-covered glaciers increasingly resilient to climate change. However, debris cover also allows melt water lakes to develop on the surface and in front of glaciers. These lakes are dammed by unstable moraine ridges (a mass of earth and rocks carried along by a glacier and left when it melts), which fail catastrophically from time to time. The resulting Glacial Lake Outburst Floods (GLOFs) can be huge, in some cases killing people and destroying infrastructure 100 kilometres downstream of the lake. With continued glacier melting, GLOFs will also increase the risk to valuable infrastructure such as hydro-electric power schemes which are being built in large numbers in the Himalayas with little consideration of the nature and the extent of glacier risks. Understanding these processes is of great importance if we are to assess the future evolution of glaciers, and changes in natural hazards and water supplies.

The importance of assessing glaciers as a means of understanding their role in regional and catchment hydrology and as the focus of natural hazards is now being recognised internationally. Glaciers and ice caps constitute Essential Climate Variables (ECV) within the Global Climate Observing System (GCOS) and its terrestrial component, the Global Terrestrial Observing System (GTOS), both recognised by the United Nations Framework Convention on Climate Change (UNFCCC). GCOS and GTOS were set up in 1992 and 1996 respectively. Under both the systems, several interrelated scientific groups are monitoring glaciers in all the world’s major mountain regions, and this must continue to provide the evidence base to develop successful climate mitigation and adaptation policies.

Eventually, glaciers should be seen as important global assets, that provide climate services and support ecological services along with a range of economic, cultural and political systems. They should also be viewed as central to climate litigation programmes where developing countries use glacier melting as evidence to garner support in climate negotiations and in climate change adaptation and reparation discussions.

In the end, climate change has the potential to disrupt entirely the context within which economic and political decision-making operates. Few people outside of science recognise the extreme rapidity with which climate can change and the non-linear and dynamic nature of the climate system. Politicians have consistently failed to listen to the warnings or take them seriously. This means climate change is likely to have some very unpleasant future surprises in store for us and glacier melting will be one of the first and most important manifestations of this.

Stephan Harrison is associate professor in Quaternary Science at College of Life and Environmental Sciences, University of Exeter, the UK. He is also the director of Climate Change Risk Management, a specialist scientific consultancy

(This story was first published in the May 1-15, 2017 issue of Down To Earth magazine.)

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