Preprints
https://doi.org/10.5194/tc-2021-348
https://doi.org/10.5194/tc-2021-348

  24 Nov 2021

24 Nov 2021

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

Calibration of basal melt on past ice discharge lowers projections of Antarctica’s sea level contribution

Eveline C. van der Linden1, Dewi Le Bars1, Erwin Lambert1, and Sybren Drijfhout1,2 Eveline C. van der Linden et al.
  • 1Royal Netherlands Meteorological Institute, Utrechtseweg 297, 3731 GA, De Bilt, The Netherlands
  • 2Institute for Marine and Atmospheric Research Utrecht, Department of Physics, Utrecht University, Princetonplein 5, 3584 CC, Utrecht, The Netherlands

Abstract. Antarctic mass loss is the largest contributor to uncertainties in sea level projections on centennial timescales. In this study the contribution of Antarctica’s ice discharge to future sea level changes is computed with ocean thermal forcing from 14 earth system models and linear response functions from 16 ice sheet models for three greenhouse gas emission scenarios. Different than in previous studies, basal melt was calibrated on observed Antarctic ice discharge rather than on basal melt itself with an iterative approach. For each model combination, a linear and quadratic melt dependency were calibrated both regionally (in five Antarctic sectors) and at the continental scale. Projections using all model combinations show that the variation in basal melt computation methods affect the projected sea level more than the scenario variations (SSP1-2.6 to SSP5-8.5). After calibration, a high number of model pairs still underestimated ice discharge in hindcasts over 1979–2017. Therefore top 10 % best-performing model combinations were selected for each method. A comparison between these model selections shows that the quadratic melt parameterisation with Antarctic-wide calibration performs best in reproducing past ice discharge. We conclude that calibration of basal melt on past ice discharge combined with model selection makes projections of Antarctic ice discharge (more) consistent with observations over the past four decades. Moreover, calibration of basal melt on past ice discharge results in lower basal melt sensitivities and thus lower projections of Antarctica’s sea level contribution than estimates of previous multi-model studies.

Eveline C. van der Linden et al.

Status: open (until 19 Jan 2022)

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Eveline C. van der Linden et al.

Eveline C. van der Linden et al.

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Short summary
The Antarctic ice sheet is the largest source of uncertainty in sea level projections on centennial timescales. The Antarctic ice sheet mainly loses mass through ice discharge; the transfer of land ice into the ocean. Ice discharge is triggered by warming ocean water (basal melt). In this study, new projections of Antarctic ice discharge are presented that are made consistent with observations. This results in lower projections of the Antarctic sea level contribution than in previous studies.