Improved knowledge of the contributing sources of uncertainty in projections of Arctic sea ice over the 21st century is essential for evaluating impacts of a changing Arctic environment. Here, we consider the role of internal variability, model structure and emissions scenario in projections of Arctic sea-ice area (SIA) by using six single model initial-condition large ensembles and a suite of models participating in Phase 5 of the Coupled Model Intercomparison Project. For projections of September Arctic SIA change, internal variability accounts for as much as 40%–60% of the total uncertainty in the next decade, while emissions scenario dominates uncertainty toward the end of the century. Model structure accounts for 60%–70% of the total uncertainty by mid-century and declines to 30% at the end of the 21st century in the summer months. For projections of wintertime Arctic SIA change, internal variability contributes as much as 50%–60% of the total uncertainty in the next decade and impacts total uncertainty at longer lead times when compared to the summertime. In winter, there exists a considerable scenario dependence of model uncertainty with relatively larger model uncertainty under strong forcing compared to weak forcing. At regional scales, the contribution of internal variability can vary widely and strongly depends on the calendar month and region. For wintertime SIA change in the Greenland-Iceland-Norwegian and Barents Seas, internal variability contributes 60%–70% to the total uncertainty over the coming decades and remains important much longer than in other regions. We further find that the relative contribution of internal variability to total uncertainty is state-dependent and increases as sea ice volume declines. These results demonstrate that internal variability is a significant source of uncertainty in projections of Arctic sea ice.

对于评估21世纪北极海冰变化的不确定性的成因，应加深了解，这对于评估不断变化的北极环境的影响至关重要。在这里，我们通过使用六个单一模型初始条件大集合和一组参与耦合模型比对的第5阶段的模型，来考虑内部可变性，模型结构和排放情景在北极海冰面积（SIA）投影中的作用项目。对于9月北极SIA变化的预测，内部可变性占未来十年总不确定性的40％至60％，而排放情景在本世纪末占主导地位。到本世纪中叶，模型结构占总不确定性的60％至70％，到21世纪末的夏季，模型结构下降到30％。对于冬季北极SIA变化的预测，内部可变性将在未来十年内占总不确定性的50％至60％，并且与夏季相比，在更长的交货时间会影响总不确定性。在冬季，与弱强迫相比，强强迫作用下模型不确定性存在相当大的情景依赖性，而模型不确定性则相对较大。在区域范围内，内部变异性的影响范围可能很大，并且很大程度上取决于日历月份和区域。对于格陵兰岛，冰岛，挪威和巴伦支海的冬季SIA变化，内部变率在未来几十年内占总不确定性的60％至70％，并且比其他地区要重要得多。我们进一步发现，内部变异性对总不确定性的相对贡献是取决于状态的，并且随着海冰量的减少而增加。这些结果表明，内部可变性是北极海冰投影不确定性的重要来源。