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Cryosphere Lost: Vanishing Continental Glaciers Pose a Critical Threat to Humanity’s Dwindling Water Reserves and Earth’s Fragile Climate Resilience

Bopi Biddanda and Tony Weinke, Annis Water Resources Institute, Grand Valley State University, USA;
Mani Villar-Argaiz and Juanma Medina-Sánchez, Instituto del Agua and Departamento de Ecología, Universidad de Granada, Spain.

Summary: A new peer-reviewed opinion piece in the September 2023 issue of Eos published by the American Geophysical Union addresses the subject of protecting the water resources of Spain’s Sierra Nevada Mountain range that is threatened by increasing anthropogenic land use and changing climate-driven precipitation patterns over the Mediterranean. Other mountain water towers (MWT) cross the world such as the Rockies, Andes, Alps and Himalayas are similarly afflicted. These mountain-based glacial lakes, streams and rivers support a vast ecosystem of life in downstream farms, villages, towns, cities – including forests, wetlands and coastal estuarine habitats all along their watersheds. Indeed, one-half of humanity depends on mountain water resources. However, the world’s MWTs, considered the third pole, are projected to disappear by the end of the century. Thus, civilization is sleep-walking into this impending crisis of loss of freshwater availability in mountain-fed watersheds across the world. Additionally, a 2020 eLetter to Science on the accelerating and non-linear nature of continental ice-loss at the North and South poles and aerial observations of extensive meltwater lakes and streams on the Greenland Shelf reported in Eos in 2022, highlight the fact that loss of all continental glaciers on Earth is accelerating – resulting in sea level rise and attendant salinization of ground water in coastal habitats where nearly a third of us now reside. Furthermore, the loss of albedo (reflectivity) from the lack of snow and ice cover on world’s glaciers is expected to lead to a ramped-up positive loop of ever greater climate warming and accelerating glacier melt. Society needs to become urgently aware of the factors driving a vanishing cryosphere and its world-wide consequences from the sierras to the sea – and adopt timely mitigation and adaptation strategies.

World’s Mountain Glaciers and How Their Fate is Tied to Our Water Resources

The escalating impacts of both human activities and climate change are placing freshwater resources, and the myriad of ecosystem services they provide, under increasing threat. Most mountain ranges are experiencing unprecedented ice loss, with the Himalayas, the largest mountains on Earth, being particularly affected, having lost 40% of their glacier mass since the Little Ice Age (Lee et al. 2021). In the past five decades, the Alps have witnessed a decrease of 5.6% per decade in the duration of snow cover (Carrer et al. 2023). Such impacts are most visible for mountain water resources that are the source of most of world’s streams, lakes, wetlands, and major rivers – the natural mountain water towers (MWT) of the world. Mountains, which cover about a quarter of Earth’s surface, provide more than half of the world’s freshwater resources. Complex mountain habitats also harbor over 85% of the world’s species of amphibians, birds and mammals – many of which are exclusive to these regions (Rahbek et al. 2019). However, because MWTs are particularly sensitive to intensifying anthropogenic impacts and ongoing climate change – high altitude ecosystems are warming faster than the global average – both mountain ecosystems and downstream communities face increasing water-related uncertainties.

MWTs play a vital role because of their world-wide distribution, coupled with an immense capacity for intercepting, capturing, and storing precipitation, and distributing it to lowlands over time. Rightfully called Earth’s Third Pole, Mountains that are glaciated and periglaciated (subterranean ice reserves), even out wet and dry periods by holding water in reserve in winter and releasing it during subsequent dry and hot summer months. Mountain lakes, streams and rivers also sustain numerous fragile ecosystems such as riparian forests and biodiverse wetlands in their watersheds. Think of any of the great rivers such as the Amazon, Parana, Mississippi-Missouri, Mackenzie, Ob, Yenisei, Nile, Niger, Congo, Ganges, Indus or Yangtze – they all originate in mountain highlands and run through continental scale watersheds to the sea. However, both the quantity and quality of mountain waters, the ecosystems they sustain, and services they provide, are increasingly threatened by climate change (e.g., warming, extremes of droughts and floods, reduced rain, snow and ice or their increasing loss), unsustainable land use and water extraction, and ongoing pollution. All these factors endanger the attainment of UN sustainable development goal of Clean Water and Sanitation, which aims to provide universal and equitable access to safe and affordable drinking water, sanitation, and hygiene by 2030.

A high mountain stream in Spain’s Sierra Nevada, the southernmost glacial mountain range in Europe. Mountain headwaters and their downstream watersheds are threatened by changing snowfall and rainfall trends and increasing human impact. Water from MWTs is even more critical in arid regions such as the Mediterranean. Photo Credit: María del Carmen Fajardo-Merlo, Agencia de Medio Ambiente y Agua de Andalucía, Spain.

Even though different mountain ranges of the world experience change differently, there are many common ongoing effects, such as depleting MWTs and degrading mountain and downstream ecosystems. These trends are in step with decreasing winter ice cover in lakes across the northern hemisphere that leads to increased interannual variability in water flow. For example, in recent years, southern Spain has been experiencing increasingly milder winters, hotter springs, and drier summers that include heat waves. Additionally, water quality in the Sierra Nevada watershed has deteriorated over the last few decades, in synch with increased human appropriation of water and recurring drought events. Many of these watershed observations, made on the mountains and in downstream locations of the Sierra Nevada, generally mimic those taking place in mountain ecosystems globally (Andes, Rockies, Alps, Himalayas, etc.). The most vulnerable MWTs are also where population densities are highest.

The Randolph Glacier Inventory is a compilation of all the World’s glaciers (https://eoimages.gsfc.nasa.gov/images/imagerecords/83000/83918/global_glaciers_rgi_lrg.jpg Open link and click continental subregions such as Indonesia and New Zealand to view regional glaciers). Credit: NASA Earth Observatory https://nsidc.org/learn/parts-cryosphere/glaciers

Concurrent loss of glacial and periglacial ice is a looming problem across the world, and it affects water availability, water quality, and biodiversity. Today, over 1.5 billion people around the world directly depend on water derived from glacial meltwater for their livelihoods – a resource that is becoming scarcer as mountain snowpacks that once were annually refreshing the downstream watersheds during the dry summer months shrink inexorably (Porder 2023). Furthermore, as groundwater depletion continues unabated around the world, the value of MWTs to the water balance of downstream societies and ecosystems can only increase. Preserving mountain water towers is our best insurance policy for ensuring a steadier water supply and damping the tendency for floods and droughts as the climate increasingly warms and the water cycle is perturbed – becoming less predictable. In Spain, two University of Granada-led citizen-science projects involving the public and school children address the issue of safe-guarding the water resources of the Sierra Nevada. In the 74 High Mountain Glacial Lakes project, members of the public report the status of the lakes during the summer to a common repository that creates maps of their health. The Rios de Vida program involves school children and their teachers in inventorying mountain streams and rivers in their neighborhoods, resulting in ecosystem assessments and timely public policy recommendations. The European SmartEcomountain project seeks to enhance our understanding of mountain and mountain-fed ecosystems and foster sustainable mountain natural resources. The project’s website – https://smartecomountains.lifewatch.dev/en/ – highlights various initiatives and hosts a learning hub. Similar projects in other mountainous regions of the world should help bring awareness to troubled mountain and their downstream ecosystems, shape policy and help conserve MWT resources.

Earth’s Polar Glaciers and How Their Fate is Tied to Changing Climate

The cryosphere plays a vital role in Earth’s climate regulation. At present the Earth is in a warm interglacial phase. In a warmer world, precipitation is more likely to fall as rain than snow. Indeed, continuing warming should speed up the Ice Albedo-Temperature positive feedback wherein the decrease in Earth’s reflectivity (of incoming solar radiation) will lead to further warming, further ice loss, further decrease Earth’s albedo, and so on, leading to ever warmer conditions. It is due to the high sensitivity of the Ice Albedo-Temperature feedback that maximum changes in temperature are felt first in high-latitude and high-altitude ecosystems.

Ice Albedo-Temperature Feedback: when climate warms, the decreased extent of reflective snow and ice decreases the albedo (reflectivity) of Earth’s high-latitude and high-altitude glaciers, causing further warming by positive feedback. The same feedback can work in reverse to amplify global cooling as shown in the image. Image and concept credit: Ruddiman, W. (2010). Earth’s Climate: Past and Future. Freeman & Co., pp. 441.

Evidence of decreasing polar ice-cover over the past two decades is clear setting the stage for the Ice Albedo-Temperature feedback to play. Sea level changes in Earth’s history are closely tied to changes in continental ice inventories. Current trends of accelerating glacial ice mass loss pose near (decadal scale) and long-term (millennial scale) risks to our coastal ecosystems and infrastructure. Whereas some sea level rise is compensated by isostatic rise of continents following the weight loss of its glaciers, the net effect of ice melt and warming-related expansion of seawater over the past century has been a several millimeter rise per year in global sea level.

Ice Cover: 10-year averages between 1979 and 2018 and yearly averages for 2007, 2012, and 2023 of the daily (a) ice extent and (b) ice area in the Northern Hemisphere (left image) and Southern Hemisphere (right image), and a listing of the extent and area of the current, historical mean, minimum, and maximum values in km². Credit: NASA https://earth.gsfc.nasa.gov/cryo/data/current-state-sea-ice-cover

Several recent reports emphasize the trend of accelerating warming of our planet and warn of the dangers of crossing delicate tipping points where loss of entire ecosystems and their biodiversity will further erode human well-being and climate resilience. For example, exceeding the 1.5^oC planetary warming limit would trigger multiple climate tipping points including stability of ice sheets around the world (Armstrong Mckay et al. 2022) and the State of the Climate Report caution that the Earth System is on the threshold of entering uncharted territory on multiple fronts including the reliable availability of water (Ripple et al. 2023). Indeed, the risk of crossing safe planetary boundaries and tripping multiple tipping points is being compounded by unprecedented rising temperatures that in turn greatly affect the water cycle. For example, since its original publication in 1998, the “Hockey Stick” temperature model of the last millennium has not only been validated but has been extended back another millennium and has added 2 recent decades of data reaching the present time. The “New Hockey Stick” shows that global temperature has been relatively stable for the last 2,000 years but has been rising relentlessly since the Industrial Revolution – and the rate of increase has been accelerating in recent decades (Mann 2023). These observations make scenarios arising from the risk of crossing safe planetary boundaries and multiple interconnected tipping points – such as the freshening of polar waters due to ice melt leading to a slow-down in the global ocean thermohaline circulation diminishing the capacity of the oceans to serve as a thermostat – more likely.

Hazards of Abrupt Continental Ice Loss: Glacial Lake Bursts and Sea Level Rise

Ice loss from all of Earth’s continental sources is presently accelerating. During the last glacial cycle ~20,000 years ago, the sea level was ~120 m below the current interglacial level. Loss of all current continental ice in the Antarctic, Greenland and mountain glaciers would lead to a sea level rise of ~65m. However, there is no reason to expect future ice loss will be gradual and steady. Indeed, as warming intensifies melting, incidences of glacial lake outbursts are becoming common across world’s glaciated mountain ranges – endangering downstream communities.

Large number of meltwater lakes on the glacier’s surface and the extensive network of stream channels crisscrossing the Greenland Ice Sheet on August 1, 2022. Denser and warmer surface water often bores its way through the ice all the way to the bedrock and then spreads, loosening up the icesheet from its moorings – and facilitating abrupt slide out to the sea, and ice loss. Photo credit: Juanma Medina-Sánchez, University of Granada, Spain.

Today, we’re beginning to understand the positive feedbacks in the ice-climate system such as melting dynamics on a glacier’s surface, sides and below, as well as lubricated movement by meltwater between the ice and bedrock/till. Yet, we may be underestimating future ice loss by measuring only gradual melt while not accounting for intermittent calving and slide offs of icebergs that result in massive and sudden inputs to the sea, such as Greenland’s Jakobshavn Glacier that is losing around 4 billion tons of ice to the sea each year. Whereas potential for significant episodic loss of ice by calving and slide off mechanisms is well-recognized, predicting such intermittent ice loss is difficult. For example, ice held within “threshold systems” like the vast Antarctica’s Thwaites Glacier that is currently receding present the threat of significant sea level rise tomorrow, in a few decades, or in centuries.

Addition of continental ice leads to sea level rise promptly by 9/10^th of the ice volume. Episodic losses amounting to just 1-2% of the remaining continental ice mass during the coming decades could rapidly raise sea level by ~1-2 m – possibly even triggering glaciogenic tsunami waves – putting coastal communities at immediate risk. One can correctly presume that low-elevation islands world-wide and coastal peninsulas such as Florida and Yucatan that are primarily slabs of porous limestone, will be particularly vulnerable to both sea level rise and attendant salinization of ground water. In an increasingly warming planet, the need for a better handle on non-linear processes such as abrupt continental ice loss and resulting sudden seal level rise, is certainly in the public interest.

Conclusions

Observations from all three poles of the world (North, South and Mountain glaciers) reveal accelerating loss of continental glacial mass that is possibly irreversible. Humanity needs to come to terms with the fact that much of the cryosphere may all but vanish in our lifetimes. Civilization must plan for this eventuality applying mitigation and adaptation strategies well ahead of a complete collapse of the cryosphere that plays a critical role in the global storage and distribution of water as well as climate regulation.

Highlighted Source Literature:
Biddanda,B. A., M.Villar-Argaiz and J. M. Medina-Sanchez (2023). Protecting the Mountain Water Towers of Spain’s Sierra Nevada. Eos, American Geophysical Union. 104 (9), 18-21. September 2023. https://eos.org/opinions/protecting-the-mountain-water-towers-of-spains-sierra-nevada
Biddanda, B. A., and A. D. Weinke (202O). Abrupt Continental Ice Loss and Sea Level Rise. Science 367 (6484), eLetter. (Note: In link below, go to bottom and click View More) https://www.science.org/doi/10.1126/science.abb5660
Medina-Sanchez, J. M. and B. A. Biddanda,B. A. (2022). Lake effect: Multitude of meltwater lakes on the Greenland Ice Sheet. Eos 103 (10), 10. https://eos.org/archive-2022

Additional Cited References:
Armstrong McKay, D. I., et al. 2022. Exceeding 1.5^oC global warming could trigger multiple climate tipping points. Science 377, eabn7950 (2022). DOI: 10.1126/science.abn7950 https://doi.org/10.1126/science.abn7950
Carrer, M. et al. 2023. Recent waning snowpacks in the Alps is unprecedented in the last six centuries. Nature Climate Change 13: 155-160 https://doi.org/10.1038/s41558-022-01575-3
Lee, E., et al. 2021. Accelerated mass loss of Himalayan glaciers since the Little Ice Age. Scientific Reports https://doi.org/10.1038/s41598-021-03805-8
Mann, K. E. 2023. Climate: Beyond the Hockey Stick. TIME November 20, 2023. P. 26.
Porder, S. 2023. Elemental: How Five Elements Changed Earth’s Past and will Shape Our Future. Princeton University Press, Princeton, New Jersey, USA.
Rahbek et al. 2019. Humbolt’s enigma: What causes global patterns of mountain biodiversity? Science 365: 1108-1113. https://www.science.org/doi/10.1126/science.aax0149
Ripple, W. J., et al. 2023. The 2023 state of the climate report: entering uncharted territory. BioScience https://doi.org/10.1093/biosci/biad080

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