Preprints
https://doi.org/10.5194/gmd-2024-121
https://doi.org/10.5194/gmd-2024-121
Submitted as: model evaluation paper
 | 
26 Aug 2024
Submitted as: model evaluation paper |  | 26 Aug 2024
Status: this preprint is currently under review for the journal GMD.

CMIP6 models overestimate sea ice melt, growth & conduction relative to ice mass balance buoy estimates

Alex Edward West and Edward William Blockley

Abstract. With the ongoing decline in Arctic sea ice extent, the accurate simulation of Arctic sea ice in coupled models remains an important problem in climate modelling. In this study, the substantial CMIP6 model spread in Arctic sea ice extent and volume is investigated using a novel, process-based approach. An observational dataset derived from the Arctic Ice Mass Balance buoy (IMB) network is used to evaluate the thermodynamic and mass balance diagnostics produced by a subset of CMIP6 models, to better understand the model processes that underlie the large-scale sea ice states. Due to the sparse nature of the IMB observations, the evaluation is performed by comparing distributions of modelled and observed fluxes in the densely sampled regions of the North Pole and Beaufort Sea.

We find that all fluxes are routinely biased high in magnitude with respect to the IMB measurements by nearly all models, with too much melt in summer, and too much conduction and growth in winter, even as a function of ice thickness. We also show that choices of thermodynamic parameterisation substantially influence particular fluxes in physically realistic ways, and that these effects likely modulate the large-scale relationship between ice thickness and ice growth and melt in the CMIP6 models.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Alex Edward West and Edward William Blockley

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2024-121', John Toole, 11 Sep 2024
  • RC2: 'Comment on gmd-2024-121', Mathieu Plante, 14 Oct 2024
Alex Edward West and Edward William Blockley
Alex Edward West and Edward William Blockley

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Short summary
This study uses ice mass balance buoys – temperature and height-measuring devices frozen into sea ice – to find how well climate models simulate the melt & growth of, and conduction of heat through, Arctic sea ice. This may help understand why models produce varying amounts of sea ice in the present day. We find models tend to show more melt, growth or conduction for a given ice thickness than the buoys, though the difference is smaller for models with more physically realistic thermodynamics.