Unhealthy and out of shape: Deciphering the slow response of glaciers to climate change
Creators: name: Wettstein, Christian Alexander
Publisher: name: ETH Zurich
Year: 2023
Subjects: glacier melt
Climate change
info:eu-repo/classification/ddc/550
Earth sciences

description: Ongoing climate change has resulted in substantial glacier volume loss worldwide. Due to their slow adjustment to temperature changes, glaciers are largely in imbalance with the current climate. Hence, they reflect a mixture between past and current climate variability combined with anthropogenic forcing. Due to this delayed response, glaciers in the European Alps will for instance lose 50% of their mass by 2050, largely irrespective of the climate scenario. The retreat of glaciers has a severe impact on sea level rise, water supply, natural catastrophes like glacier lake outburst floods, hydro-electricity production and tourism. Therefore, predicting the future retreat for glaciers is of great importance in order to quantify the effect of climate mitigation measures and to perform adequate risk management. A widely accepted method to assess the response time of these ice masses is to rely on the e-folding time. This is the time it takes for a glacier to complete 1-e−1 (=63%) of its volume/area change from an initial state to a perturbed one.
In this study, the regional e-folding time is examined for all regions belonging to the Randolph Glacier Inventory, which divides the Earth into 19 distinct regions based on glacier cover- age. This e-folding time is calculated from GlacierMIP3 experiments, in which different glacier models simulated the advance or retreat for various climate scenarios over multi-millenial time scales. This long time horizon allows glaciers to reach a state of equilibrium which contrasts with current approaches from the literature, where glacier loss is typically only simulated until the end of the century, a time scale over which these ice masses are far from steady state. Simulations from eight different glacier models indicate that the most important parameter to describe the regional response time is the region’s mean slope. Areas with a mean slope below 13% yield an e-folding time far greater than 100 years, whereas steeper regions suggest faster e-folding times below 100 years. In case of a 75% relative volume loss (between current state and final steady state volume), the Low Latitude region adapts to warming the fastest with an e-folding time of 10.8 ± 1.0 years. In contrast, the Russian Arctic corresponds to the slowest region for the same volume loss scenario, with an e-folding time of 281.4 ± 88.5 years.
The examined models in GlacierMIP3 are based on different glacier-modelling methods to simulate the mass balance and the resulting advance or retreat. Half of the models follow a volume-area scaling approach in which ice flow is neglected, while the others incorporate these ice dynamics. We found that volume-area scaling models generally yield faster e-folding times than the ones accounting for ice flow, with GLIMB being an exception. In fact, GLIMB pro- duces the slowest e-folding times throughout all models, despite being based on a volume-area scaling approach. This slow response could partially be due to the representation of the mass balance in GLIMB, which includes additional climate forcing parameters versus other models that typically only rely on temperature and precipitation as input.