Effusive volcanic eruptions have been common in Iceland throughout the Holocene with the largest ones happening prior to the industrial revolution. Such eruptions can affect climate through the formation of sulfate aerosols and subsequent impacts on clouds. As different atmospheric conditions modulate the cloud and climate responses to aerosol perturbations, a pre-industrial effusive eruption might have different climate impacts were it to happen today or in the future. Here we use an Earth system model to simulate the surface climate response to Icelandic effusive volcanic eruptions under pre-industrial, present day, and end of the 21st century climate conditions. For the last case, high anthropogenic greenhouse gas and aerosol emissions are assumed. We find that the climate state significantly modulates the climate response, especially in the Arctic where we model amplified surface warming during winter under pre-industrial conditions and stronger surface cooling during summer in warmer climates.

Despite the complexity of the physical mechanisms behind precipitation, many studies linking precipitation to weather types or atmospheric circulation focus on a single variable, oversimplifying the interactions involved. An alternative, multivariate approach to examining various aspects of precipitation generation is through the use of air masses (AMs). The gridded weather typing classification (GWTC-2) is a synoptic weather typing/air mass classification scheme that captures the holistic, multivariate nature of weather at any given time and location, utilizing multiple atmospheric variables. This study examined the association between precipitation and GWTC-2 air masses (AMs) on regional to global scales-the first use of the GWTC-2 AMs to study precipitation. Although regional differences exist, AMs modulate precipitation over land more than in oceanic areas. There is also a noticeably weaker association between AMs and tropical precipitation compared to extratropical precipitation, where up to 60% of summer precipitation variability is explained. Also, land precipitation is better modulated by AMs than oceanic precipitation. Regarding individual air mass influences, Humid Warm AMs surprisingly poorly correlate with land precipitation, likely because water vapor does not increase linearly with higher temperatures over land. Also, compared to the other two humid AMs, the Humid Cool AM contributes 5x more precipitation in deserts. More interestingly, the frontal AMs, defined to capture migrating extratropical cyclones, strongly contribute to tropical precipitation and capture the West African Monsoon remarkably well. The association between GWTC-2 AMs and precipitation has potential applicability in ensemble precipitation forecasting and downscaling GCM model simulations of daily precipitation.