22 Nov 2021
22 Nov 2021
Status: this preprint is currently under review for the journal TC.

Understanding model spread in sea ice volume by attribution of model differences in seasonal ice growth and melt

Alex West1, Ed Blockley1, and Mat Collins2 Alex West et al.
  • 1Met Office Hadley Centre, FitzRoy Road, Exeter EX1 3PB
  • 2Centre for Engineering, Mathematics and Physical Sciences, University of Exeter, Stocker Road, Exeter EX4 4PY

Abstract. Arctic sea ice is declining rapidly, but predictions of its future loss are made difficult by the large spread both in present-day and in future sea ice area and volume; hence, there is a need to better understand the drivers of model spread in sea ice state. Here we present a framework for understanding differences between modelled sea ice simulations based on attributing seasonal ice growth and melt differences. In the method presented, the net downward surface flux is treated as the principal driver of seasonal sea ice growth and melt. A system of simple models is used to estimate the pointwise effect of model differences in key Arctic climate variables on this surface flux, and hence on seasonal sea ice growth and melt. We compare three models with very different historical sea ice simulations: HadGEM2-ES, HadGEM3-GC3.1 and UKESM1.0. The largest driver of differences in ice growth / melt between these models is shown to be the ice area in summer (representing the surface albedo feedback) and the ice thickness distribution in winter (the thickness-growth feedback). Differences in snow and melt-pond cover during the early summer exert a smaller effect on the seasonal growth and melt, hence representing the drivers of model differences in both this and in the sea ice volume. In particular, the direct impacts on sea ice growth / melt of differing model parameterisations of snow area and of melt-ponds are shown to be small but non-negligible.

Alex West 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-2021-351', Anonymous Referee #1, 18 Dec 2021
  • RC2: 'Comment on tc-2021-351', Anonymous Referee #2, 22 Feb 2022

Alex West et al.

Data sets

Code associated with submitted paper: "Understanding model spread in sea ice volume by attribution of model differences in seasonal ice growth and melt " Alex West

Alex West et al.


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Short summary
In this study we explore a method of examining model differences in ice volume by looking at the seasonal ice growth and melt. We use simple physical relationships to judge how model differences in key variables affect ice growth/melt, and apply these to three case study models with ice volume ranging from very thin to very thick. Results suggest that differences in snow and meltpond cover in early summer are most important in causing the sea ice differences for these models.