Volcanic eruptions and viking society

How did volcanic eruptions and their climate impact shape the early history and society of Scandinavia?

The period 500-1250 Common Era (CE) is characterized by societal unrest, Viking expansion, emerging kingship - and large volcanic eruptions evidenced by geochemical markers in natural archives. The climate variations in Europe, especially in Scandinavia during this period, are however poorly resolved even on a timescale of centuries. Moreover, available dating of archaeological findings from that time has never been interpreted within a framework of climatic and environmental change. Within the VIKINGS project, researchers at the Department of Geosciences at the University of Oslo aim to understand how volcanic eruptions and climate change shaped the early history of Europe.

— We seek to reveal the climate of this intriguing historic period and to address the role of volcanic eruptions in triggering environmental changes by applying paleoclimate, volcanology, and archaeological records. With the help of Sigma2, we can run and store high-resolution climate models and data (daily output at 100 km) trying to answer the above-raised question, says Professor Kirstin Krüger, who is leading the VIKINGS project.

During the last 8000 years, extremely cold periods have occurred, which according to the climate model simulations can only be explained by a series of large explosive volcanic eruptions. Volcanic-induced multi-centennial cold periods occurred every once or twice per millennia throughout this Holocene period (van Dijk, 2022). The fourth coldest of these long-lasting cold periods took place during the mid-6th century. Targeted Earth System Climate model runs were carried out for the period 520 CE to 660 CE to test if volcanic eruptions, in particular the volcanic double event in 536 CE and 540, CE led to a decadal up to a centennial cooling over Scandinavia and Europe. The so-called Late Antiquity Little Ice Age lasted from the mid-6th to the 7th century. The VIKINGS project’s model results reveal that there is a pronounced cooling over Scandinavia lasting approximately 20 years in the model experiments with the new and improved volcanic forcing data set from the 6th assessment report of the Intergovernmental Panel on Climate Change. The pronounced surface climate cooling over Scandinavia may have led to the Norse mythology of the “Fimbulwinter” (Gundersen, 2022).

These climate model simulations combined with a growing-degree-day model and local pollen records reveal that this cooling had a severe impact on societies in Southern Norway for up to 20 years (van Dijk et al 2022). The mountainous inland study area as well as the west coast of Norway experienced a reduction in agricultural activity and farm abandonment, whereas in the Oslo fjord area (Raknehaugen mound) agriculture and society were hardly affected (van Dijk et al 2023).