Abstract
Regional climate variability manifests through distinct atmospheric regimes influencing weather, climate, and predictability. Yet, their response to global warming remains unresolved. Using a hundred realisations from the Community Earth System Model Large Ensemble, we examine shifts in wintertime North Atlantic atmospheric regimes and the North Atlantic Oscillation before and after 1995, highlighting the detectable influence of anthropogenic warming on atmospheric circulation. The large-ensemble framework isolates internal variability by removing the ensemble mean. Under anthropogenic warming, the number of regime states associated with the forced response remains constant, although their spatial circulation patterns undergo substantial reorganisation. In contrast, internal variability alone exhibits a reduction in the number of regime states. Future projections indicate a shift toward more frequent positive phases of the North Atlantic Oscillation, accompanied by low-amplitude negative phases late in the century, alongside a marked decline in its variability and altered mid-tropospheric westerlies.
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Data availability
The CESM2-LE model output is available from: (https://www.cesm.ucar.edu/community-projects/lens2/data-sets). The observed Hurrell NAO PC-based index for model validation can be retrieved from: (https://climatedataguide.ucar.edu/climate-data/hurrell-north-atlantic-oscillation-nao-index-pc-based).
Code availability
The codes used to produce the results in this study are publicly available through the Zenodo repository: (https://doi.org/10.5281/zenodo.18030386)91.
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Acknowledgements
The CESM2-LE simulations were conducted on the IBS/ICCP supercomputer “Aleph,” a 1.43 petaflops high-performance Cray XC50-LC Skylake computing system with 18,720 processor cores, 9.59 PB storage, and 43 PB tape archive space. We also acknowledge the support of KREONET. This study was supported by the Institute for Basic Science (IBS), Republic of Korea, under IBS-R028-D1. C.L.E.F. was also partially supported by the National Research Fund of Korea funded by the Korean government (MSIT) (No. RS-2024-00416848 and NRF-2022M3K3A1097082). Also, V.V. acknowledges funding from the European Union Horizon Project EXPECT (grant 101137656).
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C.L.E.F., S.S.S., and V.V. designed the study. S.S.S. conducted the analysis, produced figures, and wrote the initial draft of the manuscript. C.L.E.F., V.V. and T.O.K. contributed to the discussion and interpretation of results. All authors contributed to the editing and reviewing of the manuscript.
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Satpathy, S.S., Franzke, C.L.E., Verjans, V. et al. Anthropogenic climate change leads to a pronounced reorganisation of wintertime North Atlantic atmospheric circulation regimes. Commun Earth Environ (2026). https://doi.org/10.1038/s43247-026-03180-0
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DOI: https://doi.org/10.1038/s43247-026-03180-0
