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.
Highlights
20 Arctic sea ice has undergone dramatic changes in recent decades, with a decline of 0.88 x 106 km2 per decade in September extent observed from 1979-2020 according to the HadISST.2.2 dataset (Titchner and Rayner, 2014) and associated thinning in summer and winter (Lindsay and Schweiger, 2015)
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; there is a need to better understand the drivers of model spread in sea ice state
Within CMIP6 HadGEM3-GC3.1 was run at multiple resolutions: in this study, we evaluate the low-resolution configuration, HadGEM3-GC3.1-LL (Kuhlbrodt et al, 2018), for consistency with UKESM1.0 -LL which was run at low resolution only
Summary
20 Arctic sea ice has undergone dramatic changes in recent decades, with a decline of 0.88 x 106 km per decade in September extent observed from 1979-2020 according to the HadISST.2.2 dataset (Titchner and Rayner, 2014) and associated thinning in summer and winter (Lindsay and Schweiger, 2015). We use a system of simple models to understand the ways in which differences in individual model variables drive differences in the surface flux, and in the 50 sea ice growth and melt. We use the framework to separate the effects of model differences in sea ice area and thickness on sea ice growth and melt (representing the two most important feedbacks of the sea ice state, the surface albedo feedback and thickness-growth feedback) from the effects of model differences in other Arctic climate variables (representing, in a sense, external forcing of the Arctic sea ice state).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
