Global glacier shrinkage accelerated

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An international research team with the participation of ETH Zurich demonstrates: Almost all glaciers worldwide are becoming increasingly thinner and losing mass – and at an ever faster pace. The investigation is the most comprehensive and most accurate of its kind to date.

Glaciers are a sensitive and obvious indicator of climate change. Regardless of the altitude or latitude, the glacial ice has been melting rapidly since the middle of the 20th century. But the scale of the disappearing ice was previously only recorded to a very limited extent and was not complete. Now an international research team led by ETH Zurich and the Université de Toulouse presents a comprehensive study on global glacier shrinkage, which was published online in the "Nature" journal on 28 April. This investigation is the first of its kind to include all glaciers in the world - around 220,000 - with the exception of the Greenland ice cap and Antarctica. It has an unprecedented spatial and temporal resolution - and it shows how quickly the glaciers have lost their thickness and mass over the past two decades.

Increasing sea levels and water shortages
The volume of the once never-ending ice has shrunk almost everywhere. Between 2000 and 2019 the glaciers worldwide lost on average a total of 267 gigatonnes (billions of tonnes) of ice per year. With this volume the territory of Switzerland would be six metres under water every year. In addition, the loss of mass has accelerated rapidly in this time. While glaciers lost 227 gigatonnes of ice per year between 2000 and 2004, the loss of mass between 2015 and 2019 was 298 gigatonnes per year. The glacier melt caused up to 21 percent of the measured sea-level rise, i.e. roughly 0.74 mm every year. Almost half of the sea-level rise can be attributed to the thermal expansion of the warming water, the remaining third can be traced to melt water of the Greenland ice cap and Antarctica, as well as changes in water reservoirs on land masses.

Some of the fastest melting glaciers are located in Alaska, Iceland and the Alps. The mountain glaciers of the Pamir, Hindu Kush and Himalayas mountain regions are also severely affected. "The situation in the Himalayas is particularly worrying. In the dry season major rivers such as the Ganges, Brahmaputra and Indus are largely supplied by glacier melt water. At the moment the increase in melt water acts as a buffer for the people in the region. However, if the Himalayan​ glaciers continue to melt at an increasing pace, densely populated countries such as India or Bangladesh could face water or food shortages in a few decades", says lead author Romain Hugonnet from ETH Zurich and the University of Toulouse. The results can now be used to improve hydrological models and make more accurate forecasts at a local and global level, e.g., in order to estimate how much melt water can be expected from Himalayan​ glaciers in the coming decades.

To their surprise the researchers also identified areas where the melt rates slowed down between 2000 and 2019, e.g., on the east coast of Greenland, in Iceland and Scandinavia. The researchers attributed this to a weather anomaly in the North Atlantic. From 2010 to 2019 this resulted in higher precipitation and lower temperatures locally, which curbed the volume of ice lost. The research team also revealed that the so-called Karakorum ​anomaly is disappearing. Before 2010 the glaciers in this mountain range were stable or they even increased. The current study shows that the Karakorum​ glaciers are now also losing mass.

Stereo satellite images as a basis
The researchers used images taken by the multispectral instrument ASTER on board the Nasa ​satellite "Terra" from 700 kilometres high as a basis for this study. The satellite has been orbiting the earth every 100 minutes since 1999. Using two cameras the ASTER instrument captures pairs of so-called stereo images which allow the researchers to create high-resolution digital elevation models of all glaciers in the world in terms of time and space. With the aid of the ASTER ​image archive, the researchers were able to reconstruct time series of the heights of the glaciers and based on this calculate the thickness​ and mass changes of the ice over time.

Lead author Romain Hugonnet, PhD student at ETH Zurich and the University of Toulouse, worked on this project for around three years. He analysed the satellite data for 18 months. In order to prepare the data, the researchers used a high-performance computer from the University of Northern British Columbia. The results will be included in the next status report of the IPCC, which is to be published this year. "Our findings are important on a political level. The world must now actually lend a hand so that we can still resist the worst in terms of climate change", says co-author Daniel Farinotti, Head of the Glaciology ​Group at ETH Zurich and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL.

Along with the University of Toulouse, ETH and the WSL, researchers from Ulster University (UK), the University of Oslo and the University of Northern British Columbia, Canada were also involved in the study (full list of participating institutions: see bibliography).

ETH Press Release

Bibliography: Hugonnet R, McNabb R, Berthier E, Menounos B, Nuth C, Girod L, Farinotti D, Huss M, Dussaillant I, Brun F, Kääb A. Accelerated global glacier mass loss in the early twenty-first century, Nature, published online on 28 April 2021. DOI: 10.1038/s41586-​021-03436-z

Weltweiter Gletscherschwund hat sich beschleunigt - Umwelt Perspektiven, retrieved on 29.04.2021

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