Modelling future glacier evolution: Which feedbacks are relevant?

Numerous models to project the future evolution of mountain glaciers in response to ongoing climate change are available, both at the local and the global scale. However, a suite of partly major simplifications is necessary in these models given the restrictions in data availability. Whereas most models account for the primary feedbacks, such as the snow-ice albedo feedback and the dynamic glacier response in some way, a considerable number of yet poorly understood or less investigated feedbacks is present that might significantly hamper the reliability of current glaciological projections.

 

Here, we present results of a detailed modelling study for the example of Vadret da Morteratsch, Swiss Alps. A surface mass balance model accounting for ice dynamics is forced with downscaled regional climate model output (68 scenarios, CH2018) for the period 2015 to 2100. Various processes are either parameterized or explicitly accounted for. We focus on the use of a fully distributed surface energy-balance approach in comparison to simplified degree-day methods. The relevance of projected changes in different components of the energy balance is assessed using model experiments. In particular, the importance of feedback effects due to (1) the spatio-temporal evolution of supraglacial debris, (2) the formation of new proglacial lakes, and (3) changes in bare-ice albedo and local direct solar irradiance is investigated.

 

We find that the above feedback effects all have a rather small potential to substantially impact on the rates of expected glacier retreat. In some cases, this is unexpected (e.g. for debris coverage and proglacial lakes) but can be explained by compensating processes. We also discuss and visualize the future wastage of Vadret da Morteratsch under the newest generation of climate scenarios, and put these results into context with previous studies, as well as with plans to artificially reduce the rate of glacier mass loss.