State-Dependent North Atlantic Response to Volcanic Eruption Clusters

Paleoclimate reconstructions suggest that clusters of volcanic eruptions may trigger sustained cooling events, but the underlying mechanisms and their potential dependence on the mean climate state remain poorly understood. Here, we investigate the climate response to an idealized eruption cluster using two coupled climate models under fully glacial, deglacial, and pre-industrial conditions. While the global mean temperature responses are largely climate-state independent, North Atlantic cooling is stronger under glacial conditions, especially in the Hadley Centre Model HadCM3. This response is primarily driven by a sustained weakening of the Atlantic Meridional Overturning Circulation due to increased surface buoyancy and sea-ice extent. However, the magnitude and duration of this response vary with climate state and model, due to differences in upper-ocean stability, convection zones, and sea-ice cover. Our results suggest that while volcanic clusters can induce intense cooling, they alone cannot sustain Younger Dryas-like climate shifts.

Plain Language Summary
Paleoclimate reconstructions suggest that volcanic eruptions occurring in close succession, known as a volcanic eruption cluster, may trigger prolonged cooling events. However, the physical mechanisms driving this potential response remain unclear. The effect of the background climate (i.e., mean temperature, sea-ice cover, ocean-atmosphere circulation etc.) is also poorly understood. Here, we examine the climate response to an idealized volcanic eruption cluster using the Hadley Centre Coupled Model (HadCM3) and the Max Planck Institute Earth System Model under fully glacial, deglacial, and pre-industrial conditions. We find that the climate response to a volcanic eruption cluster depends not only on the mean state of the climate, but also on model characteristics, including the representation of upper-ocean temperature and salinity, the location and strength of deep convection sites, and sea-ice extent. Our results show that the global mean temperature responses are largely independent of the mean climate state in both models, but the response in the North Atlantic is highly model dependent. HadCM3 shows a stronger and more persistent cooling in the North Atlantic in already cold climates. Overall, for the volcanic cluster in the two models used in our study, volcanic forcing alone is not sufficient to sustain a millennial-scale cooling event.