Revisiting the volcanic forcing of high-latitude Northern Hemisphere eruptions

Large high-latitude explosive volcanic eruptions remain less well understood than their low-latitude counterparts, despite their potential for strong hemispheric climate impacts. Using the high-top coupled Earth system model CESM2-WACCM6 with prognostic stratospheric aerosols and chemistry, we simulate Pinatubo-magnitude Northern Hemisphere (NH) volcanic eruptions at 64° N. We show how the SO₂ lifetime and growth of volcanic sulphate aerosols are strongly modulated by the initial state of the NH polar vortex for eruptions at this latitude. The resulting variability of the volcanic forcing is of comparable magnitude to its sensitivity to varying the plume composition, eruption season, and plume height. We compare the modelled volcanic sulphate deposition over the Greenland ice sheet to that assumed in current forcing reconstructions of past NH extratropical eruptions and provide a new model-based estimate of the magnitude and uncertainty of the transfer function used to reconstruct sulphur injections from such eruptions. Our results demonstrate the great potential for improvement in understanding and reconstructing the climatic impacts of NH high-latitude eruptions.