23 Mar 2022
23 Mar 2022
Status: a revised version of this preprint is currently under review for the journal TC.

The contribution of Humboldt Glacier, North Greenland, to sea-level rise through 2100 constrained by recent observations of speedup and retreat

Trevor R. Hillebrand1, Matthew J. Hoffman1, Mauro Perego2, Stephen F. Price1, and Ian M. Howat3,4 Trevor R. Hillebrand et al.
  • 1Fluid Dynamics and Solid Mechanics Group, Los Alamos National Laboratory, Los Alamos, NM, 87545, USA
  • 2Center for Computing Research, Sandia National Laboratories, Albuquerque, NM 87185, USA
  • 3Byrd Polar and Climate Research Center, Columbus, OH, 43210, USA
  • 4School of Earth Sciences, Ohio State University, Columbus, OH, 43210, USA

Abstract. Humboldt Glacier, North Greenland, has retreated and accelerated through the 21st century, raising concerns that it could be a significant contributor to future sea-level rise. We use a data-constrained ensemble of three-dimensional higher-order ice sheet model simulations to estimate the likely range of sea-level rise from the continued retreat of Humboldt Glacier. We first solve for basal traction using observed ice thickness, bed topography, and ice surface velocity from the year 2007 in a partial differential equation constrained optimization. Next, we impose calving rates to match mean observed 2007–2017 retreat rates in a transient calibration of the exponent in the power-law basal friction relationship. We find that power law exponents in the range of 1/7–1/5 — rather than the commonly used 1/3–1 — are necessary to reproduce the observed speedup over this period. We then tune an iceberg calving parameterization based on the von Mises stress yield criterion in another transient calibration step from 2007–2017 to approximate both observed ice velocities and terminus position in 2017. Finally, we use the range of basal friction relationship exponents and calving parameter values to generate the ensemble of model simulations from 2007–2100 under three climate forcing scenarios from CMIP5 (two RCP 8.5 forcings) and CMIP6 (one SSP5-8.5 forcing). Our simulations predict 5.5–9.2 mm of sea-level rise from Humboldt Glacier, significantly higher than a previous estimate (~3.5 mm) and equivalent to a substantial fraction of the 40–140 mm predicted by ISMIP6 from the whole Greenland Ice Sheet. Our larger future sea-level rise prediction results from the transient calibration of our basal friction law to match the observed 2007–2017 speedup, which requires a semi-plastic bed rheology. In many simulations, our model predicts the growth of a sizable ice shelf in the middle of the 21st century. Thus, atmospheric warming could lead to more retreat than predicted here if increased surface melt promotes hydrofracture of the ice shelf. Our data-constrained simulations of Humboldt Glacier underscore the sensitivity of model predictions of Greenland outlet glacier response to warming to choices of basal shear stress and iceberg calving parameterizations. Further, transient calibration of these parameterizations, which has not typically been performed, is necessary to reproduce observed behavior. Current estimates of future sea-level rise from the Greenland Ice Sheet could, therefore, contain significant biases.

Trevor R. Hillebrand et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2022-20', Anonymous Referee #1, 09 May 2022
    • AC1: 'Reply on RC1', Trevor Hillebrand, 29 Jun 2022
  • RC2: 'Comment on tc-2022-20', Anonymous Referee #2, 01 Jun 2022
    • AC2: 'Reply on RC2', Trevor Hillebrand, 29 Jun 2022

Trevor R. Hillebrand et al.

Data sets

MPAS-Albany Land Ice model simulations of Humboldt Glacier, North Greenland, from 2007–2100 Trevor R. Hillebrand, Matthew J. Hoffman, Mauro Perego, Stephen F. Price

Model code and software

MPAS-Albany Land Ice model simulations of Humboldt Glacier, North Greenland, from 2007–2100 Trevor R. Hillebrand, Matthew J. Hoffman, Mauro Perego, Stephen F. Price

Trevor R. Hillebrand et al.


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Short summary
We estimate that Humboldt Glacier, North Greenland, will contribute 5.5–9 mm to global sea-level from 2007–2100, using an ensemble of model simulations constrained by observations of glacier retreat and speedup. This is a significant fraction of the 40–140 mm from the whole Greenland Ice Sheet predicted by the recent ISMIP6 multi-model ensemble, suggesting that calibrating models against observed velocity changes could result in higher estimates of 21st century sea-level rise from Greenland.