Super-Volcanic Eruptions May Not Cause Catastrophic Cooling

Climate simulations have suggested that catastrophic global cooling follows volcanic super-eruptions, yet no evidence has been found in archaeological and paleoclimate records. Here we show that climate simulations of these rare eruptions are unreliable because too little information regarding volcanic aerosols is preserved to sufficiently constrain their climatic influence. Ice core sediments provide some constraint on the injected amount of sulfur that forms sunlight-blocking aerosol, yet no record exists of the size of these aerosol particles. Here we show that aerosol size is a major factor controlling the post-eruption surface temperature anomalies, as it sets the balance between counteracting aerosol interactions with solar and terrestrial radiation. Models with interactive aerosol chemistry and microphysics have been used to estimate supervolcanic aerosol size, yet the available studies widely disagree on the size that develops. As we demonstrate, this disagreement in aerosol size is the primary reason these models fail to constrain the severity of supervolcanic cooling. Lastly, we raise two unexamined possibilities from our own model explorations of the poorly constrained parameter space. Firstly, we show that it is possible that no super-eruption is capable of causing severe cooling, no matter how much sulfur it injects: super-eruptions may thus cause no more cooling than eruptions that have occurred in the Last Millennium. Second, we show that there is a limited possibility that the largest super-eruptions cause widespread warming, rather than cooling.