Arctic response to high-latitude effusive volcanic eruptions depends on the climate state

Effusive volcanic eruptions are relatively gentle compared to explosive eruptions, resembling boiling stews rather than fireworks. They often last weeks, or even years, and can emit large amounts of gases into the lower atmosphere, among them sulphur dioxide. Through these emissions, they can impact climate via formation of sulphate aerosols and subsequent impacts on clouds. This was, for example, observed during the 2014-15 Holuhraun eruption in Iceland.

 

Volcanic eruptions with considerable effusive components have been common during the historical period in Iceland (the last ca. 1100 years), with roughly 20% of the more than 200 identified eruptions being either purely effusive or mixed effusive-explosive. The largest of those (e.g. 10th-century Eldgjá and 1783-84 Laki) occurred prior to the industrial revolution, when anthropogenic influences on the climate were smaller than they are today. As different atmospheric conditions modulate the cloud and climate responses to aerosol perturbations, a large 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 an idealized Icelandic effusive volcanic eruptions, similar to 2014-15 Holuhraun, under pre-industrial (1850; PI), present day (2010; PD), and future (2090, SSP3-7.0; Ft) climate conditions and find that this is indeed the case.

 

The modulating effects of the climate state are especially prominent in the Arctic. During winter, we simulate stronger Arctic surface warming under PI conditions, compared to PD and Ft, as the background PI clouds are thinner and hence more transparent to longwave radiation. During summer, we find that the sea ice area significantly modulates the surface cooling in the Arctic, with more Arctic sea ice under PI conditions resulting in weaker surface cooling compared to PD and Ft conditions. We further model a significant increase in sea ice area, as a result of volcanic perturbations, during summer and fall across climate states through increased shortwave cloud shielding.

 

The different surface air temperature responses in the Arctic between different climate states are rather due to a warmer climate as a result of anthropogenic greenhouse gas emissions, with subsequent changes in cloud properties (during winter) and decreased sea ice (during summer), than changes in the background aerosol state.