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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/tc-2019-68
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2019-68
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 Jun 2019

Research article | 03 Jun 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Initialization of a global glacier model based on present-day glacier geometry and past climate information: an ensemble approach

Julia Eis1, Fabien Maussion2, and Ben Marzeion1,3 Julia Eis et al.
  • 1Institute of Geography, University of Bremen, Bremen, Germany
  • 2Department of Atmospheric and Cryospheric Sciences, University of Innsbruck, Innsbruck, Austria
  • 3MARUM - Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany

Abstract. To provide estimates of past glacier mass changes over the course of the 20th century, an adequate initial state is required. However, empirical evidence about past glacier states at regional or global scale is largely incomplete, both spatially and temporally, calling for the use of automated numerical methods. This study presents a new way to initialize the Open Global Glacier Model from past climate information and present-day glacier states. We generate a large set of physically plausible glacier candidates for a given year in the past (e.g. 1850 in the Alps). All these candidates are modelled forward to the date of the observed glacier outline, and evaluated by comparing the results of the forward runs to the present-day states. We apply the approach on 2621 alpine glaciers and determine error estimates of the method from synthetic experiments. The results show that the solution is often non-unique, as many of the reconstructed initial states converge towards the observed state in the year of observation. We find that the median state of the best 5 percent of all acceptable states is a reasonable best estimate. The accuracy of the method depends on the type of the considered observation for the evaluation (glacier length, area, or geometry). Trying to find past states from only present-day length instead of the full geometry leads to a sharp increase in uncertainty. Our method thus also provides quantitative information on how well the reconstructed initial glacier states are constrained through the combination of present-day outlines with past climate conditions. We show that even with perfectly known but incomplete boundary conditions the problem of model initialization is non-trivial and non-unique, and discuss ways to develop the method further.

Julia Eis et al.
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Short summary
To provide estimates of past glacier mass changes over the course of the 20th century, an adequate initial state is required. This study presents a new way to initialize the Open Global Glacier Model from past climate information and present-day glacier states. We show that even with perfectly known but incomplete boundary conditions the problem of model initialization is non-trivial and non-unique, and discuss ways to develop the method further.
To provide estimates of past glacier mass changes over the course of the 20th century, an...
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