Preprints
https://doi.org/10.5194/tc-2021-394
https://doi.org/10.5194/tc-2021-394

  04 Jan 2022

04 Jan 2022

Review status: this preprint is currently under review for the journal TC.

A probabilistic framework for quantifying the role of anthropogenic climate change in marine-terminating glacier retreats

John Erich Christian1,2, Alexander A. Robel2, and Ginny Catania1 John Erich Christian et al.
  • 1Institute for Geophysics, University of Texas at Austin
  • 2School of Earth and Atmospheric Sciences, Georgia Institute of Technology

Abstract. Many marine-terminating outlet glaciers have retreated rapidly in recent decades, but these changes have not been formally attributed to anthropogenic climate change. A key challenge for such an attribution assessment is that if glacier termini are sufficiently perturbed from bathymetric highs, ice-dynamic feedbacks can cause rapid retreat even without further climate forcing. In the presence of internal climate variability, attribution thus depends on understanding whether (or how frequently) these rapid retreats could be triggered by climatic noise alone. Our simulations with idealized glaciers show that in a noisy climate, rapid retreat is a stochastic phenomenon. We therefore propose a probabilistic approach to attribution and present a framework for analysis that uses ensembles of many simulations with independent realizations of random climate variability. Synthetic experiments show that century-scale climate trends substantially increase the likelihood of rapid glacier retreat. This effect depends on the timescales over which ice dynamics integrate forcing. For a population of synthetic glaciers with different topographies, we find that external trends increase the number of large retreats triggered within the population, offering a metric for regional attribution. Our analyses suggest that formal attribution studies are tractable and should be further pursued to clarify the human role in recent ice-sheet change. We emphasize that early-industrial-era constraints on glacier and climate state are likely to be crucial for such studies.

John Erich Christian et al.

Status: open (until 01 Mar 2022)

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John Erich Christian et al.

John Erich Christian et al.

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Short summary
Marine-terminating glaciers have recently retreated dramatically, but the role of anthropogenic forcing remains uncertain. We use idealized model simulations to develop a framework for assessing the probability of rapid retreats in the context of natural climate variability. Our analyses show that century-scale anthropogenic trends can substantially increase the probability of such retreats. This provides a roadmap for future studies to formally attribute recent glacier change to human activity.