Glacier Loss Day as an indicator of glacier health

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View of Hintereisferner on June 23, 2018 (left) and June 23, 2022 (right). 2018
View of Hintereisferner on June 23, 2018 (left) and June 23, 2022 (right). 2018 is considered a bad year for the mass balance of the glacier. In 2022, however, the situation is dramatically worse again, as there is hardly any protective snow cover left already in June ©
In the summer of 2022, one of Tyrol’s largest glaciers recorded its largest mass loss ever. The Hintereisferner in the Ötztal valley reached its Glacier Loss Day (GLD) earlier than ever before. GLD serves as an indicator of a glacier’s health over the course of the year, similar to how Earth Overshoot Day measures the Earth’s resource consumption. A team of glacier researchers led by Annelies Voordendag at the Institute of Atmospheric and Cryospheric Sciences at the University of Innsbruck is using state-of-the-art laser scanning techniques to determine GLD.

The Hintereisferner in the rear Tyrolean Ötztal has been closely observed for more than 100 years, and there have been continuous records of its mass balance since 1952. This makes it one of the best-studied glaciers in the Alps and has been an important field of research in glacier and climate research at the University of Innsbruck for decades. Since 2016, researchers have also been collecting glacier data using a state-of-the-art system that is unique in the world: the surface of the glacier is scanned daily with a terrestrial laser scanner that monitors changes in the height of the glacier’s surface. In this way, the change in volume of the Hintereisferner is tracked in real time. Innsbruck glacier researcher Annelies Voordendag led the on-site measurements at Hintereisferner, and the results have now been published as a highlight article in the journal The Cryosphere.
ÜEarly in the summer of 2022, it became apparent that the day when the ice covered in winter begins to melt will be reached very soon. We call this day Glacier Loss Day, or GLD for short. It is comparable to Earth Overshoot Day - that day when we use more natural resources than the Earth can renew in a year," explains Annelies Voordendag. Daily monitoring of a glacier’s volume and mass changes allows a quick assessment of its current state.

Monitored glaciers

The earlier Glacier Loss Day occurs, the more time there is until the end of the summer for the glacier to lose volume and thus mass. "We track the daily volume changes with the automated terrestrial laser scanner over the glacier and determine the day when the mass gained during the winter has been lost," Voordendag says. In 2022, the GLD was measured on June 23. In the two previous years, 2021 and 2020, the GLD was not reached until mid-August. Even in years with negative balance extremes - such as 2003 and 2018 - this day was not reached until late July. Even if not every summer in the future will necessarily be like the one in 2022, the trend is clear for the glacier researchers, as the developments are outside the normal range of variation: "These are clear signals of climate change due to man-made global warming and the consequences of our greenhouse gas emissions, which are already hitting us full force today," adds Rainer Prinz of the Ice and Climate Working Group in Innsbruck. Future development forecasts also do not paint an encouraging picture. "In 10 to 20 years, only half of the Hintereisferner will be left," the team summarizes in its study.

Voordendag, A., Prinz, R., Schuster, L., and Kaser, G.: Brief communication: The Glacier Loss Day as an indicator of a record-breaking negative glacier mass balance in 2022, The Cryosphere, 17, 3661-3665,­-3661-2023 .
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