Hidden glacier melt found in Himalaya has critical implications

A new study published in the journal Nature Geoscience reveals that the mass loss of lake-terminating glaciers in the greater Himalaya has been significantly underestimated. The researchers found that the previous assessment underestimated the total mass loss of these glaciers by 6.5%. This oversight was largely due to the limitations of satellite imaging in detecting underwater changes, which has led to a knowledge gap in our understanding of the full extent of glacier loss.

The study was conducted by an international team including researchers from the Chinese Academy of Sciences (CAS), Graz University of Technology (Austria), the University of St. Andrews (UK), and Carnegie Mellon University (USA). The researchers found that the most significant underestimation of 10% occurred in the central Himalaya, where glacial lake growth was the most rapid. A particularly interesting case is Galong Co, with a high underestimation of 65%.

From 2000 to 2020, proglacial lakes in the region increased by 47% in number, 33% in area, and 42% in volume. This expansion resulted in an estimated glacier mass loss of around 2.7 Gt, equivalent to 570 million elephants, or over 1,000 times the total number of elephants in the world. This loss was not considered by previous studies since the utilized satellite data can only measure the lake water surface but not underwater ice that is replaced by water.

“These findings have important implications for understanding the impact of regional water resources and glacial lake outburst floods,” said study lead author ZHANG Guoqing from the Institute of Tibetan Plateau Research, CAS.

By accurately accounting for mass loss from lake-terminating glaciers, the researchers are able to more accurately assess the annual mass balance of these glaciers compared to land-terminating ones. This further highlights the accelerated glacier mass loss across the greater Himalaya.

The study also highlights the need to understand the mechanisms driving glacier mass loss and the underestimated mass loss of lake-terminating glaciers globally, which is estimated to be around 211.5 Gt, or roughly 12%, between 2000 and 2020.

“This emphasizes the importance of incorporating subaqueous mass loss from lake-terminating glaciers in future mass-change estimates and glacier evolution models, regardless of the study region,” said study co-author Tobias Bolch from Graz University of Technology.

David Rounce, a co-author from Carnegie Mellon University, noted that in the long run, the mass loss from lake-terminating glaciers may continue to be a major contributor to total mass loss throughout the 21st century as glaciers with significant mass loss may disappear more rapidly compared to existing projections.

“By more accurately accounting for glacier mass loss, researchers can better predict future water resource availability in the sensitive mountain region,” said YAO Tandong, who co-chairs Third Pole Environment (TPE), an international science program for interdisciplinary study of the relationships among water, ice, climate, and humankind in the region and beyond.

The findings of this study have important implications for understanding the impact of regional water resources and glacial lake outburst floods. “The underestimation of mass loss from lake-terminating glaciers means that our understanding of the full extent of glacier loss in the greater Himalaya has been limited,” said ZHANG Guoqing. “This is due to the limitations of satellite imaging in detecting underwater changes, which has led to a knowledge gap in our understanding of the full extent of glacier loss.”

The researchers found that a previous assessment underestimated the total mass loss of lake-terminating glaciers in the greater Himalaya by 6.5%. The most significant underestimation of 10% occurred in the central Himalaya.

The loss of glaciers due to climate change has significant implications for the planet. Glaciers play an important role in regulating global climate and weather patterns, and their loss can lead to a range of environmental, social, and economic consequences.

One of the most immediate and direct impacts of glacier loss is the reduction of water supplies in areas that rely on glacier-fed rivers for drinking water, agriculture, and hydropower. This can lead to water scarcity, food insecurity, and energy shortages, particularly in arid and semi-arid regions.

Glacier loss can also increase the risk of natural hazards, such as glacial lake outburst floods, which occur when meltwater accumulates behind a glacier or moraine and then breaches the dam, causing catastrophic flooding downstream. Such events can be devastating, causing loss of life, damage to infrastructure, and disruption to livelihoods.

In addition to these local impacts, glacier loss contributes to global sea level rise, as melting glaciers and ice sheets add water to the oceans. This can have significant implications for coastal communities, which may experience increased flooding, erosion, and storm surges, as well as loss of habitat and biodiversity.

Finally, glacier loss can also affect the global climate system, as glaciers reflect sunlight back into space, helping to cool the planet. As glaciers disappear, less sunlight is reflected, leading to a positive feedback loop in which warming temperatures cause more glacier melt, which in turn causes more warming.

Overall, the loss of glaciers due to climate change is a complex and multifaceted issue, with significant implications for the planet and for human societies. Understanding the mechanisms driving glacier loss and developing effective strategies for mitigating its impacts will be critical in the coming decades.

Image Credit: HUANG Cheng

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