Estimating sea-level rise from glacier mass loss

Posted by Jan-Hendrik Malles on March 4, 2021

Estimating sea-level rise from glacier mass loss is not as trivial as it might seem. That is not only because there are various (hydrological) processes that can prevent the meltwater from directly ending up in the oceans (e.g. formation of glacial lakes/dams, percolation, etc.), but due to other aspects as, e.g., the different densities of ice, freshwater, and ocean water. Another issue is the fact that some of the global glacier ice is situated below sea-level, which needs to be accounted for in order not to overestimate sea-level changes due to glacier mass loss. Moreover, ice of glaciers that drain into the ocean is likely to produce icebergs. Because melt-/freshwater has a lower density than the ocean water that is displaced by the iceberg, a small part of the sea-level rise that is produced by such icebergs will occur with a delay over the time they are melting. This is known as a halosteric effect. A competing effect is the thermosteric one, which describes the fact that ice melt that is induced by extracting the necessary latent heat from the ocean will cause a contraction of the ocean water due to the implied cooling (Jenkins, A., and Holland, D., 2007).

In this Jupyter Notebook I compare various approaches to calculating sea-level rise from glacier mass loss, respecting the density and volume below sea-level issues described above. I put the links to the data and notebook below in case you want to play around with it yourself.

The equations proposed in the Notebook should theoretically be a bit sounder than previously used in Farinotti et al., 2019. Yet, the quantitative differences are quite small globally (2.4 mm SLR, 0.8%), but can reach 4% regionally.

You can find the data here and the raw notebook here.

References

Farinotti, D., Huss, M., Fürst, J.J. et al. (2019). A consensus estimate for the ice thickness distribution of all glaciers on Earth. Nat. Geosci., 12, 168–173. doi:10.1038/s41561-019-0300-3.

Jenkins, A., and Holland, D. (2007). Melting of floating ice and sea level rise, Geophys. Res. Lett., 34, doi:10.1029/2007GL030784.