Preprints
https://doi.org/10.5194/egusphere-2024-3309
https://doi.org/10.5194/egusphere-2024-3309
20 Nov 2024
 | 20 Nov 2024
Status: this preprint is open for discussion.

An assessment of the disequilibrium of Alaskan glaciers

Daniel R. Otto, Gerard H. Roe, and John Erich Christian

Abstract. The finite response time of alpine glaciers means that glaciers will be in a state of disequilibrium in the presence of a climate trend. Using a simple model of glacier dynamics, we use metrics of glacier geometry to evaluate the present-day disequilibrium for a population of 5600 alpine glaciers in Alaska. Our results indicate that glaciers throughout the region are in a severe state of disequilibrium. We estimate that the median glacier has only undergone 27 % of the retreat necessary to achieve equilibrium with the present-day climate. In general, glaciers with smaller areas have smaller response times, and so are closer to equilibrium than large glaciers. Because much of Alaska’s glacier area is contained in a few large glaciers that are far from equilibrium, and because the rate of warming has increased in the last ~50 years, the median equilibration weighted by area is only 16 %. Our estimates are sensitive to uncertainty in response time and to the shape of the warming trend. Uncertainty is greatest for intermediate glacier response times but is small for glaciers with the smallest and largest response times. Finally, we demonstrate that accounting for the increased rate of warming in the late-20th century is important for estimating glacier disequilibrium, whereas the shape of the warming trend in the early-20th century is less relevant. Our results imply substantial future glacier retreat is already guaranteed regardless of the trajectory of future warming.

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Daniel R. Otto, Gerard H. Roe, and John Erich Christian

Status: open (until 15 Jan 2025)

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Daniel R. Otto, Gerard H. Roe, and John Erich Christian

Model code and software

Code and data release D. R. Otto https://doi.org/10.5281/zenodo.13968460

Daniel R. Otto, Gerard H. Roe, and John Erich Christian

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Short summary
Glaciers respond slowly to changes in climate, meaning that they are not yet adjusted to the present-day level of warming. Using a simple model, we find that the median Alaskan glacier has undergone only 27 % of the retreat necessary to equilibrate to the current climate. Our findings hold even when accounting for large uncertainties, suggesting that substantial retreat is inevitable even if future warming slows or stabilizes.