What the Newest Global Glacier-Volume Estimate Means for High Mountain Asia

sunset Himalaya on GlacierHub
The sun setting over the Himalayas (Source: Pixabay).

Recent advances in remote sensing and computational power have allowed scientists to overcome a stubborn obstacle, which limited their ability to calculate the total volume of glacier ice in the world. Since satellites look down on the world’s glaciers, total area is simpler to measure. But to estimate volume, it is necessary to know how thick glaciers are. As climate change progresses, ice thickness data can help researchers develop more accurate estimates of global glacier volume, and in turn, regional freshwater reserves and potential contribution to sea-level rise.

Producing accurate ice-thickness estimates, however, has proven difficult. In the absence of direct measurements for most of the world’s glaciers, previous studies primarily relied on models built from thickness estimates obtained by using ice-penetrating radar. These show that glaciers that are larger in area also tend to be thicker.

Gokyo Ri summit Gokyo Valley Nepalese Himalayas on GlacierHub
Looking down from the summit of Gokyo Ri at the Gokyo Valley, located just west of Nepal’s largest glacier, with the Himalayas in the distance (Source: Sebastian Preußer/Flickr).

In a recent study in Nature Geoscience, researchers used, for the first time, a five-model ensemble to measure the ice thickness distribution of the world’s 215,000 glaciers, excluding the Greenland and Antarctic ice sheets. They estimated the total global glacier volume at 158,000km2. When broken down by region, they found that High Mountain Asia (HMA), comprised of the Tibetan Plateau and neighboring mountain ranges, has 27 percent less ice than previously thought and could lose at least half of its glacier area by the mid 2060s.

“In light of the importance of glacier melt for regional water supply, these differences are unsettling,” remarked the researchers in the study.

Much as a traffic helicopter can measure the speed of cars by comparing photos taken over intervals, which allow them to trace individual cars, recent satellite imagery allows scientists to observe specific features on the surface of glaciers as they progress downslope. Researchers used the Randolph Glacier Inventory (RGI) 6.0, which contains surface topography information for 215,000 glaciers. Then, they employed principles of surface ice flow dynamics—for example, thicker ice moves faster, and ice overall moves faster when the slope of a mountain is steeper—to obtain estimates of ice thickness.

Muztagh Ata Pamir Mountains on GlacierHub
Muztagh Ata, also known as the “Father of Ice Mountains,” which is the second-highest peak in the Pamir Mountains, at the northern edge of the Tibetan Plateau. The mountain has easily accessible glaciers and is a popular spot for climbers (Source: David Stanley/Flickr).

This study builds on the results of an earlier version published in 2012, that was “mainly born out of the realization that wow, up to that stage, there was no estimate for the global glacier ice thickness distribution available at all,” Daniel Farinotti, a glaciologist at the Swiss Federal Institute of Technology in Zurich told GlacierHub. The 2012 study also used the RGI 2.0, which counted 26 percent less total glaciers, and calculated ice thickness estimates based on just one model.

The 2019 study’s volume estimate was just 7 percent less than in 2012, a gap mainly attributable to model differences. That said, the regional distribution of glacier ice volume in 2019 was much different, measuring a 24 percent increase in the Antarctic periphery, which was offset by decreases in the Arctic, the southern Andes, and the 27 percent decrease in HMA.

Matthias Huss, a glaciologist at the Swiss Federal Institute of Technology in Zurich and University of Fribourg, described to GlacierHub one way the 2019 study improved upon the results in 2012. “Whereas the 2012 study was ONE (the first) model for global glacier ice thickness distribution, in the present study FIVE different models were applied, developed by different research groups and with partly different underlying parameterizations,” he said. “This allows providing a “consensus” estimate, and to narrow down uncertainties.”

Both Farinotti and Huss agreed that the RGI 6.0, coupled with better satellite imagery, also made major contributions to the 2019 estimates, especially considering the significant differences between regions. Farinotti explained to GlacierHub how the improved RGI 6.0 could impact these estimates. “If a large glacier is split into two or more parts, the estimate thickness is significantly smaller,” he said. Farinotti also provided a concrete example, explaining that two glaciers each with an area of 10km2 would have significantly less ice volume than one glacier with a 20km2 area.

monastery Indus River Tibetan Plateau on GlacierHub
View of a Buddhist monastery on the banks of the Indus River, which provides water to 180 million people. The snow-capped mountains of the Tibetan Plateau frame the background (Source: lensnmatter/Flickr).

This study offers important findings to the hundreds of millions of people in High Mountain Asia that depend on glacier runoff as a source of freshwater. Based on the 2012 study, glacier area in HMA was likely halve by the end of the 2070s, but the new study moves this estimate up more than a decade, to the mid 2060s.

Glaciers “Knowing how thick [glaciers] are is equivalent of knowing how much cash we have in a bank account,” said Farinotti. According to this study, water reserves in High Mountain Asia are much smaller than previously believed. This could have significant impacts on how planning for future water use might take place, and highlights the importance of mitigation measures in response to rapid global climate change.

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Ice Loss, Gravity, and Asian Glacier Slowdown

A recent international study found that glaciers in high mountain Asia (HMA) are actually slowing down. Researcher Amaury Dehecq of NASA’s Jet Propulsion Laboratory and his co-authors analyzed 17 years of data from 2000 to 2017, attributing their results to widespread glacial thinning. They found that 94 percent of variability in glacial flow rates could be explained by ice thickness changes.

The study asserts that glaciers are thinning worldwide and at an increasing rate from the start of the 21st century. However, according to Dehecq, exactly how glaciers respond to mass loss on a regional scale was previously not well understood. This uncertainty highlighted the necessity of understanding the consequences of glacier thinning in a warming world and catalyzed this innovative study.

Nyenchen Tanglha mountains Tibet on GlacierHub
The Nyainqêntanglha mountains of Tibet, where some of the most significant glacier slowdown is occurring as a result of ice loss (Source: randomix/Flickr).

Trending: Velocity Over Time

Dehecq and his co-researchers measured glacier surface velocity changes with 1 million satellite image pairs from Landsat-7, obtaining annual velocities by comparing images taken one year apart over the same area. This was done through feature tracking; the researchers identified specific, recognizable features (i.e. crevasses, dirt patches), then measured how far they moved from one picture to the next. They did this over and over again, millions of times, to translate the image pairs into usable velocity data.

In all, the researchers calculated velocity changes over time for 11 subregions in high mountain Asia. The most significant glacier slowdowns were seen in the Nyainqêntanglha mountains of Tibet and in the Himalayas in India (Spiti Lahaul), with 37.2 and 34.3 percent velocity decreases per decade, respectively.

Lesser but still significant slowdowns were observed for glaciers in the following regions: West Nepal, East Nepal, Bhutan, Hindu Kush, Pamir, Tien Shan, and the inner Tibetan Plateau.

velocity map for high mountain asia glaciers on GlacierHub
Velocity changes from 2000-2016 for glaciers in high mountain Asia (Source: NASA Earth Observatory).

“It is only recently that big data crunching has allowed this hypothesis to be tested on such a grand scale,” said William Colgan, a research climatologist at the Geological Survey of Denmark and Greenland, in an interview with GlacierHub.

Noel Gourmelen, a co-author of the study and professor of glaciology at the University of Edinburgh, Scotland, emphasized the importance of data availability in allowing studies like this one to be successful in the future. “This research was possible because of sustained and open Earth Observation programs,” he said, also calling for continued support, maintenance, and expansion of programs like NASA’s Landsat and ESA’s Sentinels satellite series.

On Thin Ice

Dehecq and his co-researchers matched calculated velocity trends with observations of glacier thickness from 2000 to 2017. Data on glacier thickness is obtained by using remote sensing to create a model of glacier elevation change over time. This comparison showed a strong relationship between the two; each region that observed a decreasing velocity trend also observed a corresponding trend in ice thinning over the same time period.

Colgan also spoke to GlacierHub about the trending relationships this study revealed. “This study is some of the clearest evidence to date of the link between climate forcing and ice dynamics in land-terminating glaciers,” he said. “Based on these Himalayan observations, the study is telling us to expect widespread slowdowns in ice flow in regions where glaciers are experiencing widespread thinning; that’s most regions of land-terminating glaciers.”  

Karakoram region China on GlacierHub
Muztagh Ata and Lake Karakul in the Kunlun region, one of the few places where glaciers are advancing (Source: dreamX/Flickr).

Despite the strong relationship between thinning ice and decreasing velocity, each subregion had a slightly different magnitude of change. The researchers suggested that “regional differences in climate and glacier sensitivity to temperature,” could influence small spatial variations in the overall trend.

Accordingly, this study also found that regions with advancing glaciers are speeding up. Two adjacent regions in high mountain Asia, Karakoram and West Kunlun, experienced a positive mass balance along with slight velocity increases from 2000 to 2017.

The Glacial Pace

Mountain glaciers have a simple motivation for their downhill progression—gravity. Gravity causes the surface ice on a glacier to creep, slowly deforming and thinning the glacier as it moves down the mountain.

How fast glaciers travel on this journey is controlled by two factors: gravitational driving stress and glacier thickness. Driving stress is dependent on slope. The steeper the mountain, the stronger the gravitational force. Since surface ice moves faster than the ice underneath, ice thins as a glacier travels, meaning a glacier will get progressively slower the further it goes. That is, until it reaches an elevation where the surrounding climate is warm enough to rapidly melt the ice.

Dehecq and his co-researchers concluded that these two factors alone can be used to effectively calculate glacier surface velocity. “The strength of the link between mass loss and change in flow was surprisingly strong,” said Gourmelen. “One might have expected that changes at the base of the glacier would have played a role and impacts basal sliding of the ice, but this does not appear to be the case when looking at the HMA region as a whole.”

A Warning for Warming

Mount Kailash on GlacierHub
The sacred Mt. Kailash in Tibet and surrounding mountains are home to several glaciers that feed major rivers, lakes, and communities. Read more about Mt. Kailash on GlacierHub (Source: NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team).

A warming world means more glacial surface melting, and at higher elevations. However, surface melting also means ice thinning, which slows down the flow of glaciers due to gravity. So although less ice exists overall, there is also less ice reaching the elevation where it will melt.

The findings of this study improve knowledge of glacier feedbacks in the context of anthropogenic climate change regarding sea-level rise and the hydrology of certain regions. Glacial slowdown in high mountain Asia could potentially impact the availability of freshwater for communities in surrounding countries like Kazakhstan, Pakistan, India, Nepal, Bhutan, Tibet, and China.

Gourmelen gave GlacierHub an apt overview of the importance of understanding climate-glacier feedbacks:

“This is yet another sign of the impact of climate change on glaciers, the machine is slowing down. Glacier flow is a fundamental component of the glacier machine, it is the conveyor belt bringing ice from high elevation where it forms to lower elevation where it melts. This process impacts glacier met rates and glacier extent and is a key component of glacier modeling and hydrology. By providing a relationship between mass loss and flow change, parameterising model predicting future of glaciers and water availability will be made easier and more precise. It will also help interpreting some of the changes in glacier shape that we have observed in the last decades.”

Mauri Pelto, professor of environmental science at Nichols College and director of the North Cascades Glacier Climate Project, spoke to GlacierHub about the global implications of this study. “The key takeaway is the same we see for alpine glaciers around the globe, warming temperatures lead to mass balance losses, which is the key driver in glacier response,” he said. “A sustained negative mass balance leads to thinning, which leads to a glacier slow down whether the glacier is in the Himalaya, Alps, or Cascade Range.”

Pelto further explained his considerations for both the short and long-term implications of glacial slowdown in high mountain Asia. “In the short run the slow down will increase retreat rate. In the long run less dynamic mass transfer to lower elevations will lead to a reduction in glacier retreat,” he said.

In all, glacial slowdown could help preserve ice mass in the foreseeable future. However it could be at the cost of abundant freshwater for mountain communities.

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Irrigation a Potential Driver of Glacial Advance in Asia

Glaciers in the High Mountains of Asia (HMA), like most mountain glaciers around the world, are retreating due to climate change. However, in the Karakoram mountains of northwest HMA, glaciers have remained stable, and in some cases, have actually advanced. A recently published study in Geophysical Research Letters delved into one of the potential drivers behind this climatic irregularity, irrigation.

The idea that irrigation, a human-induced change to the environment for agricultural production, could regionally counteract climate change, another human-driven change, might seem a bit far-fetched. And to Remco J. de Kok, Obbe A. Tuinenburg, and Walter W. Immerzeel, three of the authors of the study who spoke with GlacierHub, it did at first start out as a wild idea. Nevertheless, previous studies, including Tuineburg’s own Ph.D. thesis, found that evaporation from irrigation in India was being transported by atmospheric winds to Himalayan areas where it fell as snow or rain, likely contributing to the increased glacial mass observed.

Diagram detailing how irrigation drivers glacial advances
How the presence of irrigation impacts local climate and glaciers (Source: Remco de Kok/Twitter).

The most famous of the advancing glacier areas is the Karakoram anomaly, first coined in 2005 by Ken Hewitt. According to Immerzeel, the term gained traction in subsequent remote sensing studies that partly confirmed the anomaly. As it turned out, the Karakoram range was not the only region with stable or advancing glaciers. Studies published in 2013 and 2017 also found positive mass balances in the Pamirs and the Kunlun Shan mountains northeast of the Karakorams.

Prior research pointed to atmospheric circulation patterns and a particularly seasonal pattern (precipitation was concentrated in winter). These studies were conducted across a large spatial scale, and therefore their proposed mechanisms should support stable and advancing glaciers uniformly across the region. Yet, the glaciers just south of Karakoram show some of the highest glacial melt rates in the region, notes de Kok, while at the same time glaciers in the Kunlun Shan region northeast of Karakoram exhibit positive mass balances. These differences in a relatively small geographical area led the authors to consider two hypotheses: either the glaciers are responding differently to similar climatic changes or that the glaciers are experiencing different climatic changes.

To assess these hypotheses, the authors selected China’s Tarim basin. According to de Kok, “It is adjacent to the areas of largest glacier growth and has some of the biggest increases in irrigation.” Next, the authors needed to assess whether recent irrigation increases in the basin were impacting neighboring mountain climates in a way that would be conducive to glacial growth.

Satellite image of the Tarim Basin
Satellite image of the Tarim Basin. The green to the southwest are the new irrigation areas potentially driving glacial advances (Source: Stuart Rankin/Creative Commons).

The authors utilized a regional climate model known as the Weather Research and Forecasting model, or WRF for short. The model was run under two scenarios: a historical or stagnant scenario and a recent change scenario. The historical scenario represented the difference between model runs with modern irrigation and no irrigation, along with atmospheric greenhouse gas concentrations (GHG) held at 1900 levels. On the other hand, the recent change scenario represented the intensification of irrigation over the period 2000 to 2010 and a concurrent increase in GHG concentrations.

By applying these two scenarios, the authors were able to more accurately depict climatic changes and evaluate whether the impact of irrigation is significant in comparison to climate change. The authors were then able to compare the two to see if either had a dominant influence on the regional climate.

After running the models, the first apparent impacts of irrigation were an increase in evapotranspiration, a decrease in summer daytime temperatures, and an increase in atmospheric moisture directly over the basin.

Photo of Muztagh Ata
Muztagh Ata, a mountain of over 24,000 feet in the western Kunlun Shan (Source: dreamX/Creative Commons).

Then things got interesting.

The model runs showed increased summer snowfall in Kunlun Shan, Pamir, and northeast Tibet. These increases were largest for the historical scenario with 1900 GHG levels and modern irrigation, showing that the increase was primarily caused by irrigation, not GHG. The authors also analyzed changes in net radiation, the difference between incoming solar and outgoing terrestrial radiation. Across most of HMA, net radiation increased; conversely, in Kunlun Shan, net radiation decreased. This decrease is a result of a decrease in incoming solar radiation due to increased cloud cover and the increase in snow cover, which has a high albedo.

Map showing the changes to snowfall and net radiation
Changes to snowfall and net radiation in the Tarim basin region (Source: de Kok et al.).

The decrease in net radiation was found to counteract climate change’s enhanced greenhouse effect. Strikingly, when GHG were raised to current levels and irrigation was held at zero, the model results revealed an increase in net solar radiation across the entire region, signaling that irrigation is the principal reason for negative net radiation in Kunlun Shan.

While it was clear that increases in irrigation are leading to favorable conditions for glacier growth, where was this increased moisture coming from?

Model results pointed to the hypothesized Tarim basin as the main source of the increased moisture in the Kunlun Shan. The authors were able to corroborate this by conducting two model runs for the Tarim basin, one with no irrigation and one modern irrigation, while the rest of the region was held at modern levels. These runs revealed an increase in snowfall and a decrease in net radiation only when the Tarim basin had modern irrigation, confirming its influence.

Map of moisture source for summer snowfall in the Kunlun Shan
Map detailing the moisture source areas for Kunlun Shan summer snowfall (Source: de Kok et al.).

The irrigation of the Tarim basin is creating an advantageous environment for glacial growth, but the study is unable to attribute just how much this mechanism is contributing to the positive mass balance of the Kunlun Shan, a topic that will be the focus of future research, according to de Kok.

There’s also the question of sustainability for the recent increase in irrigation in the region as groundwater becomes more and more stressed and adverse ecological impacts in the otherwise arid Tarim basin take hold. A future reduction in irrigation could be bad news for glaciers, as the authors note it might “mean that the anomalous glacier mass balance in Kunlun Shan is of temporary nature.” Nonetheless, in a world where melting glaciers have become the new norm, stable glaciers, even if fleeting, are a welcomed respite.

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Glacier Meeting in Kathmandu

A technical session in progress at the IGS Symposium.  Photo credit: Jitendra Bajracharya, ICIMOD
A technical session in progress at the IGS Symposium.
Photo credit: Jitendra Bajracharya, ICIMOD

Kathmandu, a Nepalese valley with a rich cultural and religious history, was the venue for the International Symposium on Glaciology in High-Mountain Asia early this month. From March 1 to 6, 240 scientists from 26 countries gathered there to further interdisciplinary understanding of the science of glaciers, snowpack, and permafrost in the high-mountain Asia region—the Himalayan, Hindu-Kush, Karakoram, Tien Shan, Pamir, and Tibetan Plateau mountain chains. The conference was organized by the International Glaciological Society (IGS) and hosted by the International Centre for Integrated Mountain Development (ICIMOD).

Livelihoods in high mountain Asia. Photo credit:  Jitendra Raj Bajracharya, ICIMOD.
Livelihoods in high mountain Asia. Photo credit: Jitendra Raj Bajracharya, ICIMOD.

IGS, founded in 1936, aims to stimulate interest in and encourage research into the scientific and technical problems of snow and ice in all countries; ICIMOD is a regional intergovernmental organization aimed at spreading knowledge about the impacts of climate change on the Hindu Kush Himalayas of Afghanistan, Bangladesh, Bhutan, China, India, Myanmar, Nepal and Pakistan—both their fragile ecosystems and the communities that live there.

Participants of the symposium exchanged the latest research findings on glaciers and glacier contribution to river flow in high-mountain Asia. This researched looked at past, present and future glacier change, glacier dynamics modeling and observations, glacier and snow melt and glacier hazards, among other subjects. While the coming together of so many scientists and specialists in the field helped to fill knowledge gaps across the region, additional questions were raised during the symposium. In particular, participants believe a more complete and accurate picture of glacier change must still be achieved. Field observations, improved models, inter-comparisons of models, and regional data sharing are considered among the most critical directions and needs for future research.

Young Scientist Panel at the IGS Symposium, moderated by David Molden, Director General of ICIMOD. Photo credit: Jitendra Bajracharya, ICIMOD
Young Scientist Panel at the IGS Symposium, moderated by David Molden, Director General of ICIMOD. Photo credit: Jitendra Bajracharya, ICIMOD

The high-mountain regions in Asia have been more acutely impacted by climate change than many other regions of the world in recent years, given the high concentrations of glacier ice found here. Glacial melt has overwhelmed not just regional ecosystems, but traditional livelihoods. These glaciers feed rivers that support the agriculture and livelihoods of over one billion people and are crucial for hydroelectric power generation. In addition, accelerated melting can aggravate natural hazards such as flooding and avalanches.

Creating an interdisciplinary understanding of glaciers was one of the primary focuses of the symposium. Glaciology brings together the atmospheric and hydrologic sciences, required to understand the connections between atmospheric processes and cryospheric change, as well as downstream impacts in the region. The cryosphere is defined as the part of Earth’s surface that consists of solid water, including snow cover, glaciers, ice sheets and ice caps, among other formations, and which plays a critical role in global climate and its changes. The interdisciplinary approach to glaciers in the region has provided the opportunity to capture regional and local changes in glaciers, snow and water availability.

The view of Eastern Himalaya--cryosphere. Photo credit: Asha Kaji Thaku, ICIMOD.   
The view of Eastern Himalaya–cryosphere. Photo credit: Asha Kaji Thaku, ICIMOD.

Scientists also discussed advances in measurements, modeling, and interpretation of glaciological changes in high mountain Asia, in order to better understand the impacts of these changes. While there is evidence of glacier retreat in the eastern Himalayas and glacier melt rates are projected to rise, river flows will not decline significantly in the coming decades due to projected increases in precipitation. It is one of the major findings presented at the conference. Meanwhile, scientists noticed that the Karakoram glaciers have been identified as an anomaly in the region, given that they are not experiencing retreat, something that has not yet been fully explained by scientific research. The IGS president Doug MacAyeal pointed out at the symposium that the role of debris cover and black carbon in glacier melt is still unclear, and the insufficient observations of high-altitude precipitation remains unsolved.

The results of the meeting will be published in Annals of Glaciology and through the IGS website in August.

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