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 IPCC special report on “Ocean and Cryosphere in a Changing Climate“, and AR6 WG-I, 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 1961/62 and 2015/16, 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 1961/62 to 2015/16. 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).

The global mass loss of glacier ice has increased significantly in the last 30 years and amounted to 335 billion tons of lost ice per year during the period from 2006-2016. 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 mass change estimates and related contributions to sea-level rise from 1975/76 to 2023/24. Annual mass changes in Gt (1 Gt = 10^12 kg) and global sea-level equivalents in mm sea-level rise are shown. Source: adjusted and updated from Dussaillant et al. (2024).

Fig. 3 Cumulative global glacier mass change estimates and related contributions to sea-level rise since 1975. Cumulative mass changes in Gt (1 Gt = 10^12 kg) and global sea-level equivalents in mm sea-level rise are shown with related uncertainties at 95% confidence intervals. Source: adjusted and updated from Dussaillant et al. (2024).

The WGMS uses a geostatistical approach by Zemp et al. (2020) and Dussaillant et al. (2024) to assess and correct for the bias in the glaciological sample with respect to the total glacier cover. Thereto, annual anomalies of glacier mass balance are spatially interpolated from glaciological observations and calibrated with geodetic observations, mainly from space-borne data by Hugonnet et al. (2021), for each glacier in the world. The resulting timeseries are aggregated to estimates of glacier mass changes at regional to global scale. Corresponding estimates of global and regional glacier mass changes are shown below.

Fig. 4 Glacier mass-change estimates from 2019/20 to 2023/24. The regional and global (bottom right) bar plots show the annual specific mass changes (in m w.e.) with related error bars (indicating 95% confidence intervals), with positive and negative values in blue and red, respectively. The golden line indicates the mean annual mass-change rate over the reference period (2000/01–2015/16). Positive and negative annual mass-change anomalies (with respect to reference period) are indicated in pale blue and pale red, respectively. The black values (below region names) indicate annual mass changes in Gt. Source: adjusted and updated from Dussaillant et al. (2024).

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. A recent assessment has achieved almost global coverage by geodetic observations from differencing of digital elevation models from optical sensors (Hugonnet et al. 2021). This global coverage and an improved approach to combine glaciological and geodetic observations has allowed to produce an operational global gridded product of glacier mass changes (Dussaillant et al. 2024). Corresponding estimates are shown above and the related data is distributed through the Climate Data Store of the Copernicus Climate Change Service. In regions with large glacier covers, the present estimates can be complemented with estimates from spaceborne gravity and altimetry observations (Gardner et al. 2013, Wouters et al. 2019, Jakob et al. 2021).

A community effort to reconcile regional and global glacier contributions to sea-level rise from different observational sources has been carried out within the ESA-funded Glacier Mass Balance Intercomparison Exercise (GlaMBIE), with results recently published in Nature (The GlaMBIE Team 2025).

References

Dussaillant, I., Bannwart, J., Paul, F. and Zemp, M. (2023): Glacier mass change global gridded data from 1976 to present derived from the Fluctuations of Glaciers Database. World Glacier Monitoring Service, https://doi.org/10.24381/cds.ba597449

Dussaillant, I., Hugonnet, R., Huss, M., Berthier, E., Bannwart, J., Paul, F., and Zemp, M. (2024, in review): Annual mass changes for each glacier in the world from 1976 to 2023, Earth Syst. Sci. Data Discuss. [preprint], https://doi.org/10.5194/essd-2024-323.

Gardner, A. S., Moholdt, G., Cogley, J. G., Wouters, B., Arendt, A. A., Wahr, J., Berthier, E., Hock, R., Pfeffer, W. T., Kaser, G., Ligtenberg, S. R. M., Bolch, T., Sharp, M. J., Hagen, J.-O. O., van den Broeke, M. R. and Paul, F. (2013): A Reconciled Estimate of Glacier Contributions to Sea Level Rise: 2003 to 2009, Science, 340(6134), 852–857, doi:10.1126/science.1234532.

Hugonnet, R., McNabb, R., Berthier, E., Menounos, B., Nuth, C., Girod, L., Farinotti, F., Huss, M., Dussaillant, I., Brun, F., and Kääb, A. (2021): Accelerated global glacier mass loss in the early twenty-first century. Nature 592 (7856), 726-731. doi:10.1038/s41586-021-03436-z.

Jakob, L., Gourmelen, N., Ewart, M. and Plummer, S. (2021): Spatially and temporally resolved ice loss in High Mountain Asia and the Gulf of Alaska observed by CryoSat-2 swath altimetry between 2010 and 2019. The Cryosphere 15 (4), 1845-1862. doi:10.5194/tc-15-1845-2021.

The GlaMBIE Team (2025): Community estimate of global glacier mass changes from 2000 to 2023. Nature. https://doi.org/10.1038/s41586-024-08545-z

Wouters, B., Gardner, A.S., and Moholdt, G. (2019): Global Glacier Mass Loss During the GRACE Satellite Mission (2002-2016). Front. Earth Sci., doi.org/10.3389/feart.2019.00096.

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, doi.org/10.1038/s41586-019-1071-0.

Zemp, M., Huss, M., Eckert, N., Thibert, E., Paul, F., Nussbaumer, S.U., and Gärtner-Roer, I. (2020): Brief communication: Ad hoc estimation of glacier contributions to sea-level rise from latest glaciological observations. The Cryosphere, 14, 1043-1050, doi.org/10.5194/tc-14-1043-2020.