High-latitude explosive volcanic eruptions can cause substantial cooling on a hemispheric scale. However, our current understanding of these events remains limited. In this study, we employ a whole atmosphere chemistry-climate model with prognostic stratospheric aerosols to simulate Northern Hemisphere (NH) high-latitude explosive volcanic eruptions of similar magnitude to the 1991 eruption of Mt. Pinatubo. Our simulations reveal that the lifetime of sulphur dioxide and the growth of volcanic sulphate aerosols are strongly influenced by the initial state of the NH polar vortex. The stability of the polar vortex during the first weeks after an eruption determines the latitudinal dispersion of the injected gases within the stratosphere. Consequently, interannual variability of the polar vortex stability introduces a variability in the modelled cumulative radiative forcing of more than 20 %. We also test the aerosol evolution’s sensitivity to co-injection of sulphur and halogens, injection season, and injection altitude, and show how processes related to aerosol formation, lifetime, and growth impact the resulting radiative forcing. Notably, several of the sensitivities are of similar magnitude to the variability stemming from initial conditions, highlighting the significant influence of atmospheric variability. Finally, we compare the modelled volcanic sulphate deposition over the Greenland ice sheet with the relationship assumed in reconstructions of past NH extratropical eruptions. Our analysis yields an estimated Greenland transfer function for NH extratropical eruptions of 0.44 × 10⁹ km² . If applied to ice core data, this value would produce volcanic stratospheric sulphur injections from NH extratopical eruptions 23 % smaller than in currently used volcanic forcing reconstructions. Furthermore, the uncertainty attached to the Greenland transfer function for NH extratropical eruptions, which propagates into the estimate of volcanic stratospheric sulphur injection, needs to be at least doubled to account for both atmospheric variability and unknown eruption source parameters. Our results offer insights into the complex dynamics shaping the impacts of both historical and future NH high-latitude eruptions. Furthermore, they underscore the need for more accurate representation of these events in existing volcanic forcing reconstructions, with the aim of improving our understanding of their climatic impacts.