How much are glaciers contributing to sea-level rise?
Melting ice sheets in Greenland and the Antarctic as well as ice melt from glaciers all over the world are causing sea levels to rise. For the upcoming IPCC special report on “Ocean and Cryosphere in a Changing Climate” [https://www.ipcc.ch/report/srocc/], an international research team combined glaciological field observations with geodetic satellite measurements – as available from the WGMS – to reconstruct annual mass changes of more than 19’000 glaciers worldwide. This new assessment shows that glaciers alone lost more than 9,000 billion tons of ice between 1961 and 2016, raising water levels by 27 millimetres. This global glacier mass loss corresponds to an ice cube with the area of Germany and a thickness of 30 metres. The largest contributors were glaciers in Alaska, followed by the melting ice fields in Patagonia and glaciers in the Arctic regions. Glaciers in the European Alps, the Caucasus mountain range and New Zealand were also subject to significant ice loss; however, due to their relatively small glacierized areas they played only a minor role when it comes to the rising global sea levels.
Fig. 1 Regional share of glaciers in sea-level rise from 1961 to 2016. The cumulative regional and global mass change of glaciers (in gigatons, 1 Gt = 1 000 000 000 tons) corresponds to the volume of the bubbles. Reading example: With more than 3,000 Gt, glaciers in Alaska (ALA) contributed the most to the increase in sea levels. The glaciers in South West Asia (ASW, blue bubble) were the only ones to increase in mass. Source: adjusted from Zemp et al. (2019), Nature. https://doi.org/10.1038/s41586-019-1071-0
The global mass loss of glacier ice has increased significantly in the last 30 years and currently amounts to 335 billion tons of lost ice each year. This corresponds to an increase in sea levels of almost 1 millimetre per year. The melted ice of glaciers therefore accounts for 25 to 30 percent of the currently observed increase in global sea levels. This ice loss of all glaciers roughly corresponds to the mass loss of Greenland’s Ice Sheet, and clearly exceeds that of the Antarctic.
Fig. 2 Global glacier contributions to sea-level rise from 1961 to 2016. Annual and pentadal mass-change rates (left vertical axis) and equivalents of mean global sea-level rise (right vertical axis) are shown with related error bars (indicated by shading) corresponding to 95% confidence intervals. Annual errors originate from independent sources: glaciological sample, geodetic sample, spatial interpolation and glacier area. Reading example: over the last years, global glacier contributions reached about 1 mm sea-level equivalent. Source: Zemp et al. (2019), Nature. https://doi.org/10.1038/s41586-019-1071-0
Improvements in global glacier mass-change assessment are still possible and necessary. As such, the observational database needs to be extended in both space and time. Here, the most urgent need for closing observational gaps being in regions where glaciers dominate runoff during warm/dry seasons, such as in the tropical Andes and in Central Asia, and in regions that dominate the glacier contribution to future sea-level rise, that is, Alaska, Arctic Canada, the Russian Arctic, and peripheral glaciers in Greenland and Antarctica
Zemp, M., Huss, M., Thibert, E., Eckert, N., McNabb, R., Huber, J., Barandun, M., Machguth, H., Nussbaumer, S.U., Gärtner-Roer, I., Thomson, L., Paul, F., Maussion, F., Kutuzov, S., and Cogley, J.G. (2019): Global glacier mass changes and their contributions to sea-level rise from 1961 to 2016. Nature, https://doi.org/10.1038/s41586-019-1071-0.