North Atlantic circulation and climate variability during the last glacial maximum and the last interglacial: insights from CMIP6/PMIP4 climate models

The Last Glacial Maximum (LGM) and Last Interglacial (LIG) provide insights into the response of the North Atlantic–European climate variability to strongly contrasting boundary conditions. Using six CMIP6/PMIP4 models, we compare temperature–precipitation patterns, atmospheric circulation, and variability, with emphasis on the North Atlantic Oscillation (NAO). Across climate states, the leading modes of wintertime sea-level pressure variability remain recognisable, indicating a robust dynamical structure. However, their amplitude, explained variance, and spatial positioning exhibit state dependence. During the LGM, extensive ice sheets were associated with a stronger and more spatially confined NAO dipole, southward-displaced pressure centres, and reorganised circulation patterns, reinforcing colder and drier European conditions with enhanced seasonality. The LIG exhibits a weaker NAO expression with westward-shifted pressure centres, a more zonal circulation, northward-shifted warm sea surface temperatures, and enhanced seasonality. NAO-related interannual atmosphere–ocean coupling persists across climate states, with limitations in capturing low-frequency variability within the available simulation lengths. Summer variability is substantially weaker and more heterogeneous across all periods, with the NAO losing dominance often to the East Atlantic pattern during the LGM. Inter-model differences increase considerably under LGM and LIG conditions compared to the pre-industrial period (PI), underscoring the importance of multi-model approaches and an improved representation of key processes when investigating climate variability in extreme climate states.