Modelled surface climate response to Icelandic effusive volcanic eruptions: Sensitivity to season and size

Abstract. Effusive, long-lasting volcanic eruptions impact climate through emission of gases and subsequent production of aerosols. Previous studies, both modelling and observational, have made efforts in quantifying these impacts and untangle them from natural variability. However, due to the scarcity of large and well observed effusive volcanic eruptions, our understanding remains patchy. Here we use an Earth system model to systematically investigate the climate response to high-latitude, effusive volcanic eruptions, similar to the 2014–15 Holuhraun eruption in Iceland, as a function of eruption season and eruptive size. The results show that the climate response is regional and strongly modulated by different seasons, with mid-latitude cooling during summer and Arctic warming during winter. Furthermore, as eruptions become larger in terms of sulfur dioxide emissions, the climate response becomes increasingly insensitive to variations in the emission strength, levelling out for eruptions between 20 and 30 times the size of the 2014–15 Holuhraun eruption. Volcanic eruptions are generally considered to lead to surface cooling, but our results indicate that this is an oversimplification, especially in the Arctic where we find warming to be the dominating response during fall and winter.