Glacier and Snow Loss
Receding mountain glaciers in the European Alps, American Rockies, Andes, East Africa and elsewhere were among the first identified, visible impacts of climate change.
Most of this observed retreat however arose from ongoing warming from the end of the Little Ice Age, with rising greenhouse gases only slightly speeding that retreat.
Sometime in the past 50 years however, anthropogenic climate change became the main driver of retreat for most glacier systems.
Few glaciers near the Equator, such as the northern Andes and East Africa can survive even today’s 1°C. Some of these were shrinking anyway after the last ice age; but global warming has speeded their disappearance by many centuries. Glaciers and snow in the northern Andes provided a reliable seasonal source of water, and their loss especially will impact rural populations in Peru and Chile.
Andes. Image: Dr. Heidi Sevestre
Aiguille du midi, French Alps
Mid-latitude Glaciers and Snow
Mid-latitude glaciers and snow in the Alps, southern Andes/Patagonia, Iceland, Scandinavia, New Zealand and North American Rockies can survive at 1.5°, but these glaciers will disappear almost entirely at 2°C, and snow cover decrease. For these glaciers and mountain snowpack, that half a degree spells the difference between sufficient seasonal water supply, such as in the American West, Tarim and Indus river basins; and water scarcity.
The essential watersheds of the Himalayas/Central Asia at 1.5°C maintain around half to about twothirds of their ice. At 2°C, much more will be lost, with regional impacts on water supply and increasing political instability, especially as monsoon rains become far more unpredictable at 2°C as well.
Aerial view on the transition from the Himalayas to the Tibetan Plateau.
Jana Eichel / imaggeo.egu.eu
Heidi Sevestre, University of Svalbard
Heidi Steltzer, Fort Lewis College and SROCC Lead Author
Guðfinna Aðalgeirsdóttir, University of Iceland, AR6 Lead Author
Regine Hock, University of Alaska, SROCC and AR6 Lead Author
Georg Kaser, University of Innsbruck, AR5 WG1 Lead Author
Ben Orlove, Columbia University, SROCC Lead Author and AR5 WG1 Contributing Author
Ben Marzeion, University of Bremen, SROCC Lead Author and AR5 WG1 Contributing Author
Philippus Wester, ICIMOD, AR6 Lead Author
Essential Water Supply
Glaciers and alpine snowpack have varying importance to nearby communities as a source of water for drinking or irrigation, with some contributing only afew percent over the course of a year, but of enhanced importance during dry seasons, heat waves and droughts.
Glaciers in the Andes, and those in the Indus and Tarim basins in the Greater Himalaya region, contribute most strongly to human water supply.
While the increased melting of glaciers temporarily increases water supply, eventually the decrease and ultimate loss of glacial water resources may make current economic activities, including agriculture impossible in some regions, as well as decreasing supplies for drinking water and basic household needs.
This makes extensive adaptation or even leaving retreat as the only option, including by many indigenous mountain communities.
Lyon, France, with the Alps in the background.
Glacier melt is accelerating, and expected to reach its peak in most regions sometime around 2050, after which (if temperatures rise to 2°C and beyond) eventually little or no ice remains to melt, as occurred with the Icelandic glacier Ok sometime around 2015 (picture).
Many glaciers however are disappearing every year, and with far less fanfare: in the U.S.’s Glacier National Park, only 26 of the original 150 glaciers present in 1900 still remained in 2017.
Glaciers “work” by gaining snow at higher altitude, and losing it as meltwater at lower altitude. Warming means a rise in the altitude that separates net annual gain by snowfall turning to ice, from net annual loss by melting. A threshold is crossed when that altitude rises above the glacier’s highest point. It then suffers net loss over its entire surface every year, and is doomed to eventually disappear entirely.
Many glacier systems have little resilience to rising temperatures. This is true especially in regions where climate change also leads to long-term drought such as the Tarim Basin of Northwestern China.
Glaciers such as the tropical glaciers in East Africa and the northern and central Andes are not expected to survive at even 1.5°C of warming above pre-industrial.
Figures based on Marzeion et al (2012)
Figures based on Marzeion et al. (2012)
Glaciers in western North America, the Alps, Iceland, Scandinavia, Svalbard and New Zealand similarly are unlikely to survive at 2°C of warming. However, modeling taken out to 2300 shows that 1.5°C pathways preserve at least some remnant of ice (between 10–30%) of these mid-latitude glacier systems.
High Altitude or
In regions at higher latitude or altitude (the High Mountain Asia and high Arctic glaciers) about 50–60% of glacier ice will survive even 2°C degrees of warming, with losses potentially higher in the Hindu Kush Himalayas.
However, a 1.5°C goal preserves far greater amounts; especially for key regions of India, Pakistan, northwestern China and Nepal that rely on seasonal meltwater from these high altitude glacier systems.
Snowpack, an even greater source of seasonal water supplies than the glaciers, now appears to be following a similar path of loss as mountain glaciers: with more swings and extremes of high snowfall and snow drought, but overall loss as temperatures rise above freezing at higher altitudes. This means that precipitation that would have fallen as snow in past decades, increasingly comes down as rain.
At lower elevations and latitudes, snow will fall less often or not at all; and seasonal snowpack will not form, resulting in loss of stored water in the snow itself and underground aquifers.
Mountain snow sustains water supplies for people far beyond mountain regions, travelling great distances across grasslands and deserts to densely populated coastal regions. People in cities such as Los Angeles, Marrakech and in the Ebro-Duero basin of northern Spain and Portugal are especially dependent on the water from snow.
This decreasing high-altitude snowfall has a counterpart in the very well-documented decrease in snow cover and amounts in the Arctic since 1990. In both the Arctic and mountain regions, the well-being of people and many species depends on seasonal snow cover.
In addition to threatening water supplies, decreases in snow cover negatively impact snow tourism, especially in the U.S. West, New England and central Europe. Lack of mountain snow cover also appears to be increasing risk of wildfires, as well as catastrophic events such as mudslides in the wake of such wildfires.
Benefits of 1.5°C
A sharp strengthening of NDCs in 2021 towards 1.5°C, including preferably stronger commitments in the near-term 2030 time frame, could make the difference between rapid and disruptive loss of regionally-important snow and glacier systems, and significant slowing of glacier loss that allows local communities time to adapt, even in those regions where glaciers are doomed to disappear completely at 1° or 1.5°C.
This will have greatest benefit for communities in the Andes and Central Asia that are most dependent on glaciers as a seasonal source of water for drinking and irrigation, and on economies dependent on glaciers and associated snowpack for revenue from tourism, such as the Alps and North American West.
Lyon, France, with the Alps in th ebackground.
IPCC Special Report: Global Warming of 1.5°C
IPCC Special Report on the Ocean and Cryosphere in a Changing Climate
ICCI The Cryosphere1.5° Report
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