Persistent Model Biases in the Spatial Variability of Winter North Atlantic Atmospheric Circulation.

The three leading modes of the North Atlantic atmospheric circulation explain about 70% of the winter climate variability. Although climate models generally can capture these modes, biases may induce large uncertainties in regional climate predictions. Here, we evaluate the leading winter modes simulated by CMIP5‐PMIP3 and CMIP6‐PMIP4 models from the last millennium to future scenarios in comparison with historical reanalysis and paleo‐reconstructions. The models generally have a good representation of the average spatial pattern of the North Atlantic Oscillation (NAO) while showing a larger spread in performance for the East Atlantic and Scandinavian patterns. In contrast to historical reanalysis, the simulated NAO pattern tends to be rather stationary under various climate states over the years 861–2100. Such underestimated spatial variability in the simulated NAO is directly related to the biased spatial shifts in NAO‐related regional temperature and precipitation changes, inducing uncertainties in climate projections over the North Atlantic sector. Plain Language Summary: The North Atlantic Oscillation (NAO) is the most dominant weather pattern over the North Atlantic‐European sector with profound influence on regional climate. The NAO pattern describes the changes in a low‐pressure system over Iceland and a high‐pressure system over the Azores, which are commonly known as the NAO centers of action. However, the NAO centers of action are not always fixed in these two locations, but show spatial movement over time. In this study, we compare the winter weather patterns over the North Atlantic region from the last millennium to future scenarios in climate models with reanalysis products and paleoclimate reconstructions. We find that models generally can capture the spatial structure of the NAO very well but with little changes in its location and shape over time in contrast to historical reanalysis. These biased NAO patterns in climate models can shift the modeled regional temperature and precipitation patterns associated with the NAO. This remains a challenge for the reliability of future climate projections over the North Atlantic region. Key Points: We compare the spatial variability of modeled North Atlantic climate modes over the years 861–2100 with reanalysis and reconstructed dataThe North Atlantic Oscillation (NAO) in 13 Coupled Model Intercomparison Project‐Paleoclimate Modelling Intercomparison Project models shows underestimated spatial variability compared to historical reanalysisProjections of regional temperature and precipitation may show biased patterns due to the underestimated spatial shifts in simulated NAO [ABSTRACT FROM AUTHOR]