An international team has recalculated the ice thickness of more than 200,000 glaciers worldwide: The previous assumptions have not been confirmed, especially for the Asian region. The picture shows a glacier in Kyrgyzstan.

Worldwide ice volume calculated anew

Researchers have provided a new estimate for the glacier ice volume all around the world, excluding the Greenland and Antarctic ice sheets using modern modelling methods. The conclusion: previous calculations overestimated the volume of the glaciers in High Mountain Asia. Fabien Maussion from the Institute of Atmospheric and Cryospheric Sciences is part of the research team.

Climate change is causing glaciers to shrink around the world. Reduced meltwaters from these glaciers also have downstream effects, particularly on freshwater availability. A lack of meltwater can greatly restrict the water supply to many rivers, especially in arid regions such as the Andes or central Asia, that depend on this water source for agriculture. Up-to-date information on the worldwide ice volume is needed to assess how glaciers – and the freshwater reserves they supply – will develop, and how sea levels are set to change.

Ice thickness calculated for 215,000 glaciers

An international team has now recomputed the ice thickness distribution and thus the ice volume of around 215,000 glaciers worldwide using a combination of different models. The study, in which scientists from ETH Zurich, the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), the Universities of Innsbruck and Fribourg, Erlangen and Zurich and the Indian University of Mumbai worked together, has now been published in the renowned journal Nature Geoscience. The researchers excluded sea ice and glaciers that are connected to the Greenland and Antarctic ice sheets from their calculations. "This international collaboration  enables us to provide data with unprecedented accuracy", explains Dr. Fabien Maussion, Assistant Professor at the Institute of Atmospheric and Cryospheric Sciences at the University of Innsbruck. He is the developer of one of the models that contributed data to the project, which has been running for several years.
According to the study, the combined ice volume of all considered glaciers currently amounts to some 158,000 cubic kilometres (km3). The last available estimate – dating a few years ago – was around 18 percent higher. The largest glacier ice masses (some 75,000 km3) are found in the Arctic and account for almost half of the global glacier ice volume. They include glaciers in both the Canadian and the Russian Arctic – such as those found on Baffin Island and the Novaya Zemlya archipelago – as well as glaciers along the Greenland coast and the Norwegian island of Spitsbergen.

Glaciers might retreat faster than thought

Together with Alaska, High Mountain Asia (that is the region including the Himalaya, the Tibetan Plateau and the mountains in central Asia) is home to the largest ice masses outside the Arctic, accounting for a volume of 7,000 km3 in total. The study indicates that previous calculations overestimated this volume by almost a quarter. "In light of these new calculations, we have to assume that glaciers in High Mountain Asia might disappear more quickly than we thought so far," says Daniel Farinotti, Professor of Glaciology at the Laboratory of Hydraulics, Hydrology and Glaciology (VAW) at ETH Zurich and at the WSL. Previously, researchers had estimated that the area covered by glaciers in this region would halve by the 2070s.This is now expected to happen in the 2060s – with perceptible consequences for local water supplies. The glaciers of High Asia, in fact, feed into large rivers, including the Indus, the Tarim and rivers feeding into the Aral Sea. Hundreds of millions of people depend on them.

Meltwater volumes set to diminish by up to a quarter

For the above regions and depending on the model, researchers expect summer meltwater volumes to be as much as 24 percent lower by the end of the century as they are today. "This difference is unsettling. To get a more accurate estimation of the full extent, we would need better measurements of the regional glacier volumes," Farinotti says. As things stand, only few measurements are available for the glacier ice thickness in the region, which hampers better model calibration. Based on their calculations, the researchers also deduced that if they were to melt away completely, the glaciers – or rather their meltwater – could cause global sea levels to rise by up to 30 centimetres. Between 1990 and 2010, glacier melt contributed to rise sea levels by about 1.5 centimetres.
For their analysis, the researchers used a combination of up to five independent numerical models. In these models, several sources of information – including the glacier outlines derived from satellite images and digital elevation models of the glacier surface – were combined with data about the glaciers’ flow behaviour. "The calculation of the ice volume of a glacier is associated with great challenges, since many factors play a role, such as the physics of ice flow, the climate at the glacier's location, its shape and topography. In order to calibrate the models, ice thickness measurements were also used on glaciers, but these are only available for about 1000 glaciers worldwide. Nevertheless, thanks to this international cooperation and the combination of data from the best models currently available, we are able to make more reliable forecasts for the future development of the global ice volume," explains Fabien Maussion. All data collected in this study are publicly available in a new global dataset.


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