Abstract
The variability of Arctic sea ice extent (SIE) on interannual and multi-decadal timescales is examined in 29 models with historical forcing participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6) and in 20th-century sea ice reconstructions. Results show that during the historical period with low external forcing (1850-1919), CMIP6 models display relatively good agreement in their representation of interannual sea ice variability (IVSIE), but exhibit pronounced inter-model spread in multi-decadal sea ice variability (MVSIE), which is overestimated with respect to sea ice reconstructions and is dominated by model uncertainty in sea ice simulation in the sub-polar North Atlantic. We find that this is associated with differences in models’ sensitivity to northern hemispheric sea surface temperatures (SST). Additionally, we show that while CMIP6 models are generally capable of simulating multi-decadal changes in Arctic sea ice from the mid-20th century to present day, they tend to underestimate the observed sea ice decline during the Early Twentieth-Century Warming (ETCW; 1915-1945). These results suggest the need for an improved characterization of the sea ice response to multi-decadal climate variability, in order to address the sources of model bias and reduce the uncertainty in future projections arising from inter-model spread.
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