Projections of the winter North Atlantic circulation exhibit large spread. Coupled Model Intercomparison Project archives typically provide only a few ensemble members per model, rendering it difficult to quantify reducible model structural uncertainty and irreducible internal variability (IV) in projections. We estimate using the Multimodel Large Ensemble Archive that model structural differences explain two-thirds of the spread in late 21st century (2080–2099) projections of the winter North Atlantic Oscillation (NAO). This estimate is biased by systematic model errors in the forced NAO response and IV. Across the North Atlantic, the NAO explains a substantial fraction of the spread in mean sea level pressure (MSLP) projections due to IV, except in the central North Atlantic. Conversely, the spread in North Atlantic MSLP projections associated with model differences is largely unexplained by the NAO. Therefore, improving understanding of the NAO alone may not constrain the reducible uncertainty in North Atlantic MSLP projections.

中文翻译：

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冬季北大西洋涛动多模式大型集合投影的不确定性来源

冬季北大西洋环流的预测显示出很大的传播。耦合模型比对项目档案通常只提供每个模型的几个集合成员，因此难以量化预测中可减少的模型结构不确定性和不可减少的内部可变性 (IV)。我们使用多模型大型集合档案进行估计，该模型结构差异解释了 21 世纪后期（2080-2099）冬季北大西洋涛动 (NAO) 预测中三分之二的传播。该估计受到强制 NAO 响应和 IV 中的系统模型误差的影响。横跨北大西洋，除了北大西洋中部以外，NAO 解释了由 IV 引起的平均海平面压力 (MSLP) 预测的大部分传播。反过来，NAO 在很大程度上无法解释与模型差异相关的北大西洋 MSLP 预测的传播。因此，仅提高对 NAO 的理解可能不会限制北大西洋 MSLP 预测中可减少的不确定性。