Abstract
The predictability of the Arctic sea ice is investigated at the interannual time scale using decadal experiments performed within the framework of the fifth phase of the Coupled Model Intercomparison Project with the CNRM-CM5.1 coupled atmosphere–ocean global climate model. The predictability of summer Arctic sea ice extent is found to be weak and not to exceed 2 years. In contrast, robust prognostic potential predictability (PPP) up to several years is found for winter sea ice extent and volume. This predictability is regionally contrasted. The marginal seas in the Atlantic sector and the central Arctic show the highest potential predictability, while the marginal seas in the Pacific sector are barely predictable. The PPP is shown to decrease drastically in the more recent period. Regarding sea ice extent, this decrease is explained by a strong reduction of its natural variability in the Greenland–Iceland–Norwegian Seas due to the quasi-disappearance of the marginal ice zone in the center of the Greenland Sea. In contrast, the decrease of predictability of sea ice volume arises from the combined effect of a reduction of its natural variability and an increase in its chaotic nature. The latter is attributed to a thinning of sea ice cover over the whole Arctic, making it more sensitive to atmospheric fluctuations. In contrast to the PPP assessment, the prediction skill as measured by the anomaly correlation coefficient is found to be mostly due to external forcing. Yet, in agreement with the PPP assessment, a weak added value of the initialization is found in the Atlantic sector. Nevertheless, the trend-independent component of this skill is not statistically significant beyond the forecast range of 3 months. These contrasted findings regarding potential predictability and prediction skill arising from the initialization suggest that substantial improvements can be made in order to enhance the prediction skill.
Highlights
Decadal climate prediction is a major issue in the development of strategies for societal adaptation to the changing climate
Historical simulations (HIST) is preferred to a pre-industrial control run because it accounts for changes in natural variability, which are crucial in the Arctic
Based on the CMIP5 protocol for decadal experiments, the prognostic potential predictability (PPP) of the Arctic sea ice at interannual timescale was investigated in the CNRMCM5.1 model
Summary
Decadal climate prediction is a major issue in the development of strategies for societal adaptation to the changing climate. Despite its relatively short prediction time scale, the seasonal predictability is assessed (with statistical methods as well as coupled model experiments) over several decadelong periods, exhibiting some long-evolving trends This raises the question of the impact of this trend, due to changes in boundary conditions, on the total predictability assessment. Longer-term Arctic sea ice predictability has been investigated using perfect model assumption, in which Global Climate Models (GCMs) ensemble integrations are initialized from a reference model integration (Koenigk and Mikolajewicz 2009; Holland et al 2011; Koenigk et al 2012; Tietsche et al 2013) These studies examined the upper limit of initial-value predictability and its sensitivity to the Arctic sea ice mean state (Holland et al 2011), which is an important issue in the observed rapidly changing Arctic sea ice conditions. All components are coupled through the OASIS(v3) system (Valcke 2006)
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