Jesper Sjolte

Large tropical (TROP) volcanic eruptions can influence North Atlantic climate by inducing a positive shift of the North Atlantic Oscillation (NAO), typically resulting in winter warming across northern Eurasia. However, these changes remain highly uncertain, as they may coincide with strong internal variability in Northern Hemisphere wintertime climate. In contrast, Northern Hemisphere extratropical (NHET) eruptions are proposed to have opposite impacts, but they have been comparatively less studied, and large uncertainties remain regarding the ability of climate models to capture volcanic responses. This study examines winter North Atlantic climate responses to TROP and NHET eruptions by comparing temperature and atmospheric circulation patterns from last millennium simulations with multiple proxy-based reconstructions. We find distinct differences in NAO-related climate changes in reconstructions, with TROP eruptions followed by a shift towards positive NAO and NHET eruptions associated with a negative NAO. In comparison, modelled responses exhibit a wide spread with strong dependence on the choice of volcanic forcing dataset. Notably, simulations using the latest volcanic forcing data show improved agreement with reconstructions, particularly for TROP eruptions. This model-proxy agreement provides a useful basis for investigating the mechanisms that drive positive NAO responses after TROP eruptions. However, the simulated impacts of NHET eruptions are less consistent and remain unclear. These results highlight the importance of improved volcanic forcing datasets, refined paleoclimate reconstructions, and robust statistical approaches to better constrain uncertainties in assessing volcanic impacts on North Atlantic climate.