The global ice world, or cryosphere, consists of about 220,000 glaciers in addition to sea ice and ice caps. But these glaciers are under massive threat from global warming. How massive, however, had previously only been recorded locally or regionally. An international research team led by ETH Zurich has examined the situation globally and come to a devastating conclusion: More than 5,300 gigatons of ice have disappeared in just 20 years, and at an increasing rate.
The work, which according to the authors, is the most comprehensive study on the subject of “glacier retreat”, was able to show that practically everywhere between the years 2000 and 2020 glaciers have lost volume (mass and area). The melted amount of ice could put the entire area of Switzerland six metres under water every year, according to ETH Zurich. Overall, this amount of ice has contributed about one-fifth per year to sea level rise over the past twenty years.
The researchers also calculated the speed that caused this loss. And in doing so, the results showed that the pace has picked up. This is because in the first four years of the period under review, the annual loss was just under 227 gigatonnes. This rate had risen to 298 gigatons per year by the end of the period, between 2015 and 2019. This result is also documented for the ice caps of Greenland and Antarctica.
Surprisingly, however, not all regions are equally affected by rising melt rates. For example, glaciers in East Greenland and some glaciers in Iceland and Scandinavia have been less affected, the team writes. This is probably due to weather anomalies in the North Atlantic with lower temperatures and higher snowfall amounts. However, according to the researchers, the loss in East Greenland is still 13 gigatonnes per year. The Russian Arctic, with its glaciers on the various islands along the Northeast Passage, has also melted somewhat less. The highest losses in the polar regions, however, are in Alaska (66.7 gigatonnes per year), the Canadian Arctic (57.1 gigatonnes per year) and the glaciers in Antarctica that are not part of the ice caps (20.9 gigatonnes per year). But if you add the speed, Iceland and the Alps are the hardest hit, along with Alaska and West Greenland.
The research team led by lead author Romain Hugonnet, a doctoral student at ETH Zurich and the University of Toulouse, used stereoscopic images from the ASTER module, which is attached to NASA’s Terra satellite, for the precise calculations. The orbit of this satellite is chosen in such a way that every point is captured at the same time every day. ASTER’s multispectral imagery has enabled researchers to produce accurate elevation maps of the glaciers and accurately plot the loss of elevation and area triggered by melting. By comparing this with data from NASA’s ICESat and IceBridge missions, the team obtained a chronological sequence of the mass and thickness losses of the nearly 220,000 catalogued glaciers.
The effects of this decline are not only felt in rising sea levels. Billions of people depend on glaciers for drinking water. Therefore, the focus must not only be on the dwindling ice caps and sea ice. The importance of this data from the research team is evident from the fact that it will be incorporated into the IPCC’s next State of the Climate report. “Our findings are important at the political level. The world really needs to take action now so that we can avert the worst in terms of climate change,” explains ETH and WSL glacier researcher Professor Daniel Farinotti, who is also a co-author of the study. In addition to the ETH and the University of Zurich, the University of Fribourg and the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, other institutions include the Universities of Toulouse and Grenoble, Ulster University, the University of Oslo and the University of British Columbia.
Dr Michael Wenger, PolarJournal
Link to the study: Hugonnet, R., McNabb, R., Berthier, E. et al. Accelerated global glacier mass loss in the early twenty-first century. Nature 592, 726-731 (2021). https://doi.org/10.1038/s41586-021-03436-z
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