Northern Hemisphere wintertime continental warming following large, low-latitude volcanic eruptions? No evidence from Pinatubo (1991) and Krakatau (1883)

It is widely believed that large, low-latitude volcanic eruptions cause a warming of the Northern Hemisphere continents in wintertime. We here call into question this widespread belief. We start by noting that it is based on two pieces of questionable evidence: (1) early modeling studies using low-resolutions models which failed to accurately capture the internal variability of the Northern Hemisphere atmospheric circulation and have since been invalidated by numerous studies with high-resolution models and (2) a small number of observational studies, not independently validated, examining single temperature reconstructions, and averaging small numbers of eruptions of different strengths and at different latitudes, with minimal signal-to-noise ratios. Given this problematic evidence, we here revisit the question by (1) focusing solely on the largest, low-latitude eruptions for which reliable observations of surface temperature are available and (2) analyzing several "large initial-conditions ensembles" of model simulations, to quantify the relative strength of the forced volcanic signal against the large background of internal variability. We demonstrate that neither the 1883 Krakatau eruption nor the 1991 Pinatubo eruption offer credible evidence of volcanic aerosols having caused a statistically significant warming of the Northern continents in the winter months following those eruptions.