A paper published on 11 February in Nature Geoscience has reported new estimates of the ice thickness distribution and the volume of present-day glaciers around the world (1). Based on a combination of numerical models, the researchers calculated a combined ice volume of around 158,000 cubic kilometres, which is around 18 per cent lower than the last estimates a few years ago. In particular, volumes of the largest ice masses outside the Arctic ― including Alaska, the Himalayas, the Tibetan Plateau, as well as mountains in central Asia ― were previously overestimated by nearly a quarter, according to the new findings.
Climate change is leading to rapid changes in the glaciers and ice caps outside the Greenland and Antarctic ice sheets. This could have far-reaching and potentially devastating consequences on freshwater availability, sea level changes, and regional water resources. But to fully assess the impact of these dramatic changes requires more accurate measurements of the ice volume stored within present-day glaciers.
The international team of glaciologists led by ETH Zurich and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL used five numerical models based on satellite imagery and digital elevation models of glacier surfaces combined with combined with data about “flow behaviour” of the glaciers. Sea ice and glaciers connected to the Greenland and Antarctic ice sheets were excluded, however, glaciers in the Canadian and the Russian Arctic and along the coast of Greenland coast and the Norwegian island of Spitsbergen were considered. In addition, glacier ice thickness measurements from the Glacier Thickness Database were used to calibrate the models. However, the database presently only contains information on about 1,000 out of some 215,000 glaciers worldwide.
The latest findings suggest ice in mountainous regions of Asia may be disappearing much faster than expected. Glacial ice in these regions could potentially be halved by the 2060s, which is bad news. Meltwaters from the glaciers feed into large rivers, such as the Indus and the Tarim, that hundreds of millions of people depend on for water supplies. Meltwaters are now expected to be 24 per cent lower by the end of the century than today. Moreover, if the glaciers completely melted, this would result in a 30-centimetre increase in sea levels ― which rose by 1.5 centimetres between 1990 and 2010 as a direct result of glacial melt.
In fact, until now, only one estimate previously existed on a global scale. Furthermore, individual models suffer from uncertainty; therefore, combining the results from different models can increase their robustness, according to the authors. To address this, the authors used five ice thickness estimation models to achieve an “ensemble-based estimate” for the ice thickness distribution of around 215,000 glaciers.
Better measurements of the regional glacier volumes are still needed to improve current models. Nonetheless, the results of this study will have important implications ranging from projected sea-level change rates to estimated future water availability, the authors write. Further, they suggest dedicated campaigns are needed to provide more information on data-scarce regions to improve the consistency and completeness of global datasets for glacier outlines.
(1) Farinotti, D. et al. A consensus estimate for the ice thickness distribution of all glaciers on Earth. Nature Geoscience (2019). DOI: 10.1038/s41561-019-0300-3