Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500–1250 CE (VIKINGS)

• Zoëga, Tómas; Storelvmo, Trude & Krüger, Kirstin (2025). Climate State Dependent Response to Very Large Icelandic Effusive Volcanic Eruptions. Geophysical Research Letters. ISSN 0094-8276. 52(16). doi: 10.1029/2025gl114638. Full text in Research Archive Show summary

  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.

• Ballo, Eirik Gottschalk; D’Andrea, William J.; Høeg, Helge Irgens; Loftsgarden, Kjetil; Bajard, Manon Juliette Andree & Eckhardt, Sabine [Show all 10 contributors for this article] (2025). 2000 years of climate, environmental, and societal variability in southeastern Norway from the annually laminated sediments of Lake Sagtjernet. Quaternary Science Reviews. ISSN 0277-3791. 354. doi: 10.1016/j.quascirev.2025.109232. Full text in Research Archive Show summary

  Previous Common Era (i.e., the past 2000 years) climate reconstructions from Fennoscandia have focused on northern and central areas, with scarce data from the southern areas. Using varved sediments from Lake Sagtjernet in southeastern Norway, we developed a hydrogen isotope record from sedimentary leaf waxes (n-alkanes) as a proxy for hydrogen isotopes in precipitation, which we interpret as an indicator of temperature variability over the past 2000 years. The climate reconstruction provides high, decadal resolution for the period 360–770 CE, allowing critical evaluation during the Dark Ages Cold Period (around 300–800 CE) and a cooling during the 6th century, previously suggested as the coldest period of the Common Era. Our results reveal that the most rapid drop in temperature occurred from 536 to 545 CE (+74/-90 years), corresponding in time to the 536 and 540 CE volcanic eruptions. We also document an inferred cold interval that persisted from around 650 to 710 CE (+72/-90 years). While past studies have suggested prolonged cooling during the Dark Ages Cold Period, our findings show that, on average, the climate during 360–770 CE was similar to the Common Era average in the Lake Sagtjernet record. To explore socio-environmental interactions throughout the past 2000 years, we present a pollen-based environmental reconstruction and integrate it with archaeological evidence from around Lake Sagtjernet. These analyses reveal significant societal activities such as land clearing, cereal cultivation, and large-scale iron production, which drastically altered the landscape in the Viking Age (around 800–1050 CE) and the first half of the Norwegian Middle Ages (around 1050–1350 CE). Modern cultivation practices following the Black Death (1349–1350 CE) were first established around 1470 CE and increased continuously until around 1940 CE. Intensification of societal activities through the past millennium, including iron production and modern cultivation, occurred during both warmer (Medieval Climate Anomaly; 950–1250 CE) and colder (Little Ice Age; 1450–1850 CE) periods.

• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2025). Modelled surface climate response to effusive Icelandic volcanic eruptions: sensitivity to season and size. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 25(5), p. 2989–3010. doi: 10.5194/acp-25-2989-2025. Full text in Research Archive Show summary

  Effusive, long-lasting volcanic eruptions impact climate through the emission of gases and the subsequent production of aerosols. Previous studies, both modelling and observational, have made efforts to quantify 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 2014–2015 Holuhraun eruption in Iceland, as a function of eruption season and size. The results show that the climate response is regional and strongly modulated by different seasons, exhibiting midlatitude cooling during summer and Arctic warming during winter. Furthermore, as eruptions increase in size in terms of sulfur dioxide emissions, the climate response becomes increasingly insensitive to variations in emission strength, levelling off for eruptions between 20 and 30 times the size of the 2014–2015 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 warming is found to be the dominant response during autumn and winter.

• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2025). Arctic warming from a high-latitude effusive volcanic eruption. Scientific Reports. 15(1). doi: 10.1038/s41598-025-98811-5. Full text in Research Archive Show summary

  The effusive Holuhraun eruption in Iceland emitted large quantities of sulfur into the troposphere during the fall and winter of 2014–15. Previous studies have shown that the resulting volcanic aerosols led to reduced insolation, and thus surface cooling, through increased cloud shortwave reflectance, mostly over the North Atlantic and Europe. Less attention has been paid to the Arctic, which at the time of the eruption received limited sunlight. Based on evidence from observations and model simulations, here we argue that increased cloud liquid water path and cloud cover following the 2014–15 Holuhraun eruption led to surface warming in the Arctic through trapping of longwave radiation. Our results show that sulfur emissions from the eruption led to extended lifetime of low and middle level clouds, reducing the longwave radiative cooling of the surface. This is the first time, to our knowledge, that an effusive volcanic eruption is shown to have this effect. Given the high level of volcanic activity in Iceland, these findings demonstrate the need to further investigate the climate impacts of high-latitude effusive volcanic eruptions. Moreover, marine cloud brightening through cloud seeding has been suggested as one way to combat anthropogenic climate change but, as our results suggest, such actions might have counteractive regional consequences.

• Fuglestvedt, Herman Fæhn; Gabriel, Imogen; Sigl, Michael; Thordarson, Thorvaldur & Krüger, Kirstin (2025). Revisiting the 10th-Century Eldgjá Eruption: Modeling the Climatic and Environmental Impacts. Geophysical Research Letters. ISSN 0094-8276. 52(1). doi: 10.1029/2024GL110507. Full text in Research Archive Show summary

  The 10th-century Eldgjá eruption in Iceland is the largest basaltic flood lava eruption of the Common Era. However, the extent of its impacts is unclear due to limited historical records. Combining volcanology and ice-core analyses from both recent and earlier studies, we present a gas emissions scenario for the Eldgjá eruption spanning 937 to 940 CE, co-injecting volcanic sulfur and halogens. The combined tropospheric and stratospheric sulfur emissions are 3–8 times higher than those adopted for Eldgjá in existing paleoclimate simulations. Earth system modeling of this scenario under pre-industrial conditions reveals a compound event with maximum northern extratropics surface cooling of ∼2°C in summer-autumn of 939 and 940 CE, prolonged Arctic sea ice growth, and large-scale precipitation changes, concurrent with stratospheric ozone depletion and elevated pollution. These results imply that the combined climatic and environmental effects of the Eldgjá eruption may have significantly impacted human populations at the time.

• Dijk, Evelien Van; Jungclaus, Johann; Sigl, Michael; Timmreck, Claudia & Krüger, Kirstin (2024). High-frequency climate forcing causes prolonged cold periods in the Holocene. Communications Earth & Environment. 5. doi: 10.1038/s43247-024-01380-0. Full text in Research Archive Show summary

  Understanding climate variability across interannual to centennial timescales is critical, as it encompasses the natural range of climate fluctuations that early human agricultural societies had to adapt to. Deviations from the long-term mean climate are often associated with both societal collapse and periods of prosperity and expansion. Here, we show that contrary to what global paleoproxy reconstructions suggest, the mid to late-Holocene was not a period of climate stability. We use mid- to late-Holocene Earth System Model simulations, forced by state-of-the-art reconstructions of external climate forcing to show that eleven long-lasting cold periods occurred in the Northern Hemisphere during the past 8000 years. These periods correlate with enhanced volcanic activity, where the clustering of volcanic eruptions induced a prolonged cooling effect through gradual ocean-sea ice feedback. These findings challenge the prevailing notion of the Holocene as a period characterized by climate stability, as portrayed in multi-proxy climate reconstructions. Instead, our simulations provide an improved representation of amplitude and timing of temperature variations on sub-centennial timescales.

• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthew & Krüger, Kirstin (2024). Initial atmospheric conditions control transport of volcanic volatiles, forcing and impacts. Atmospheric Chemistry and Physics (ACP). ISSN 1680-7316. 24(10), p. 6233–6249. doi: 10.5194/acp-24-6233-2024. Full text in Research Archive Show summary

  Volcanic eruptions impact the climate and environment. The volcanic forcing is determined by eruption source parameters, including the mass and composition of volcanic volatiles, eruption season, eruption latitude, and injection altitude. Moreover, initial atmospheric conditions of the climate system play an important role in shaping the volcanic forcing and response. However, our understanding of the combination of these factors, the distinctions between tropical and extratropical volcanic eruptions, and the co-injection of sulfur and halogens remains limited. Here, we perform ensemble simulations of volcanic eruptions at 15 and 64° N in January, injecting 17 Mt of SO2 together with HCl and HBr at 24 km altitude. Our findings reveal that initial atmospheric conditions control the transport of volcanic volatiles from the first month and modulate the subsequent latitudinal distribution of sulfate aerosols and halogens. This results in different volcanic forcing, surface temperature and ozone responses over the globe and Northern Hemisphere extratropics (NHET) among the model ensemble members with different initial atmospheric conditions. NH extratropical eruptions exhibit a larger NHET mean volcanic forcing, surface cooling and ozone depletion compared with tropical eruptions. However, tropical eruptions lead to more prolonged impacts compared with NH extratropical eruptions, both globally and in the NHET. The sensitivity of volcanic forcing to varying eruption source parameters and model dependency is discussed, emphasizing the need for future multi-model studies to consider the influence of initial conditions and eruption source parameters on volcanic forcing and subsequent impacts.

• Loftsgarden, Kjetil & Iversen, Frode (2024). The Impact Of The 6th Century Crisis – Exploring Burials as a Proxy For Population Dynamics in Iron Age Scandinavia. Norwegian Archaeological Review. ISSN 0029-3652. doi: 10.1080/00293652.2024.2412018. Full text in Research Archive Show summary

  This study examines population dynamics in South Norway during the Iron Age, focusing on the mid-6th century crisis and its aftermath. Analysis of nearly 7,000 dated burials reveals a substantial decline of over 75% post-6th century compared with the preceding period. Set against other archaeological data, this indicates a decline in the population of South Norway. The period of societal turmoil and decline may have started earlier, but was likely catalysed by the volcanic eruptions of 536 and 540 CE and the following colder period, and possible also by plague pandemics. The ramifications of the mid-6th century crisis were exacerbated by the population increase in the preceding periods, where the population may have been nearing its regional carrying capacity. Although devastating, the 6th century crisis may also have opened up new possibilities for those who made it through, perhaps initiating a brief period of relative social and economic equality, similar to the initial consequences of the Black Death. Contrasting with the preceding period, South Norway’s Viking Age saw ample burials, attributed to factors including a warmer climate, advanced agriculture, surplus production, trade expansion and increased slavery. The shift highlights complex interactions between environmental, economic, and social factors in the shaping of population dynamics in Iron Age South Norway.

• Fuglestvedt, Herman Fæhn; Zhuo, Zhihong; Toohey, Matthew & Krüger, Kirstin (2024). Volcanic forcing of high-latitude Northern Hemisphere eruptions. npj Climate and Atmospheric Science. 7(1), p. 1–12. doi: 10.1038/s41612-023-00539-4. Full text in Research Archive Show summary

  High-latitude explosive volcanic eruptions can cause substantial hemispheric cooling. Here, we use a whole-atmosphere chemistry- climate model to simulate Northern Hemisphere (NH) high-latitude volcanic eruptions of magnitude similar to the 1991 Mt. Pinatubo eruption. Our simulations reveal that the initial stability of the polar vortex strongly influences sulphur dioxide lifetime and aerosol growth by controlling the dispersion of injected gases after such eruptions in winter. Consequently, atmospheric variability introduces a spread in the cumulative aerosol radiative forcing of more than 20%. We test the aerosol evolution’s sensitivity to co- injection of sulphur and halogens, injection season, and altitude, and show how aerosol processes impact radiative forcing. Several of these sensitivities are of similar magnitude to the variability stemming from initial conditions, highlighting the significant influence of atmospheric variability. We compare the modelled volcanic sulphate deposition over the Greenland i

• Arthur, Frank; Hatlestad, Kailin; Lindholm, Karl-Johan; Loftsgarden, Kjetil; Löwenborg, Daniel & Solheim, Steinar [Show all 8 contributors for this article] (2024). The impact of volcanism on Scandinavian climate and human societies during the Holocene: Insights into the Fimbulwinter eruptions (536/540 AD). The Holocene. ISSN 0959-6836. 34(5), p. 619–633. doi: 10.1177/09596836231225718. Full text in Research Archive Show summary

  Recent paleoclimatic research has revealed that volcanic events around 536–540 AD caused severe, short-term global cooling. For this same period, archeological research from various regions evidences significant cultural transformation. However, there is still a lack of understanding of how human societies responded and adapted to extreme climate variability and new circumstances. This study focuses on the effects of the 536/540 AD volcanic event in four Scandinavian regions by exploring the shift in demographic and land use intensity before, during, and after this abrupt climate cooling. To achieve this, we performed climate simulations with and without volcanic eruptions using a dynamically downscaled climate model (iLOVECLIM) at a high resolution (0.25° or ~25 km). We integrated the findings with a comprehensive collection of radiocarbon dates from excavated archeological sites across various Scandinavian regions. Our Earth System Model simulates pronounced cooling (maximum ensemble mean −1.1°C), an abrupt reduction in precipitation, and a particularly acute drop in growing degree days (GDD0) after the volcanic event, which can be used to infer likely impacts on agricultural productivity. When compared to the archeological record, we see considerable regional diversity in the societal response to this sudden environmental event. As a result, this study provides a more comprehensive insight into the demographic chronology of Scandinavia and a deeper understanding of the land-use practices its societies depended on during the 536/540 AD event. Our results suggest that this abrupt climate anomaly amplified a social change already in progress.

• Hutchison, William; Gabriel, Imogen; Plunkett, Gill; Burke, Andrea; Sugden, Patrick & Innes, Helen [Show all 17 contributors for this article] (2024). High-Resolution Ice-Core Analyses Identify the Eldgjá Eruption and a Cluster of Icelandic and Trans-Continental Tephras Between 936 and 943 CE. Journal of Geophysical Research (JGR): Atmospheres. ISSN 2169-897X. 129(16). doi: 10.1029/2023JD040142. Full text in Research Archive Show summary

  The Eldgjá eruption is the largest basalt lava flood of the Common Era. It has been linked to a major ice-core sulfur (S) spike in 939–940 CE and Northern Hemisphere summer cooling in 940 CE. Despite its magnitude and potential climate impacts, uncertainties remain concerning the eruption timeline, atmospheric dispersal of emitted volatiles, and coincident volcanism in Iceland and elsewhere. Here, we present a comprehensive analysis of Greenland ice-cores from 936 to 943 CE, revealing a complex volatile record and cryptotephra with numerous geochemical populations. Transitional alkali basalt tephra matching Eldgjá are found in 939–940 CE, while tholeiitic basalt shards present in 936/937 CE and 940/941 CE are compatible with contemporaneous Icelandic eruptions from Grímsvötn and Bárðarbunga-Veiðivötn systems (including V-Sv tephra). We also find four silicic tephra populations, one of which we link to the Jala Pumice of Ceboruco (Mexico) at 941 ± 1 CE. Triple S isotopes, Δ33S, spanning 936–940 CE are indicative of upper tropospheric/lower stratospheric transport of aerosol sourced from the Icelandic fissure eruptions. However, anomalous Δ33S (down to −0.4‰) in 940–941 CE evidence stratospheric aerosol transport consistent with summer surface cooling revealed by tree-ring reconstructions. Tephra associated with the anomalous Δ33S have a variety of compositions, complicating the attribution of climate cooling to Eldgjá alone. Nevertheless, our study confirms a major S emission from Eldgjá in 939–940 CE and implicates Eldgjá and a cluster of eruptions as triggers of summer cooling, severe winters, and privations in ∼940 CE.

• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthey & Krüger, Kirstin (2023). Initial conditions control transport of volcanic volatiles, forcing and impacts. Atmospheric Chemistry and Physics Discussions (ACPD). doi: 10.5194/egusphere-2023-2374. Full text in Research Archive
• Dijk, Evelien Van; Gundersen, Ingar Mørkestøl; Bode, Anna de; Høeg, Helge Irgens; Loftsgarden, Kjetil & Iversen, Frode [Show all 9 contributors for this article] (2023). Climate and societal impacts in Scandinavia following the 536 and 540 CE volcanic double event. Climate of the Past. ISSN 1814-9324. 19(2), p. 357–398. doi: 10.5194/cp-19-357-2023. Full text in Research Archive Show summary

  In the Northern Hemisphere, the mid-6th century was one of the coldest periods of the last 2000 years, as indicated by both proxy records and Earth System Model (ESM) simulations. This cold period was initiated by volcanic eruptions in 536 CE and 540 CE. Evidence from historical sources, archaeological findings, and proxy records suggests that the extent and severity of this volcanic induced cooling was spatially heterogeneous and that the effect on society resulted in adaptation and resilience at some locations, whereas social crisis has been indicated at others. Here, we study the effect of the volcanic double event in 536 CE and 540 CE on the climate and society in Scandinavia with a special focus on Southern Norway. Using an ensemble of Max Planck Institute ESM transient simulations for 521–680 CE, the temperature, precipitation and atmospheric circulation patterns are studied. The simulated cooling magnitude is then used as input for the growing degree day (GDD) model set-up for Southern Norway. This GDD model indicates the possible effects on agriculture for three different study areas in Southern Norway, representative of typical meteorological and landscape conditions. Pollen from bogs and archaeological records inside the study area are then analysed at high resolution (1–3 cm sample intervals) to give insights into the validity of the GDD model set-up with regard to the volcanic climate impact on the regional scale, and to link the different types of data sets. After the 536/540 CE double event, a maximum surface air cooling of up to 3.5 °C during the mean growing season is simulated regionally in Southern Norway. With a worst-case scenario cooling of 3 °C, the GDD model indicates crop failures were likely in our northernmost and western study areas, while crops were more likely to mature in the southeastern study area. These results are in agreement with the pollen records from the respective areas. During the sixth century, excavations show an abandonment of farms, severe social impact but also a continuation of occupation or a mix of those. In addition, archaeological findings from one of the excavation sites suggest wetter conditions for the mid-sixth century in Scandinavia, as simulated by individual ensemble members. Finally, we discuss the likely climate and societal impacts of the 536/540 CE volcanic double event by synthesising the new and available data sets for the whole Scandinavia.

• Ballo, Eirik Gottschalk; Bajard, Manon Juliette Andree; Støren, Eivind & Bakke, Jostein (2023). Using microcomputed tomography (μCT) to count varves in lake sediment sequences: Application to Lake Sagtjernet, Eastern Norway. Quaternary Geochronology. ISSN 1871-1014. 75. doi: 10.1016/j.quageo.2023.101432. Full text in Research Archive Show summary

  Varved lake sediments are one of the most important natural archives that allow annual resolution paleoclimate reconstructions. Conventional varve counting techniques use thin sections to manually identify lamina. However, this technique is destructive, labour intensive and limited to a 2D representation of complex 3D features which may lead to misidentification of varve boundaries. This study presents the use of microcomputed tomography (μCT) scans in constructing varve chronologies, utilizing scanning resolutions of ∼50 μm (binned to ∼200 μm) for core sections up to 150 cm long. To evaluate this method, we cored and analysed Lake Sagtjernet in Eastern Norway — revealing a 593 cm-long sediment record of the past 10274 (+220/-329) years, with continuous laminations from 84 to 533 cm depth (75% of the sediments). Through limnological monitoring and microfacies analyses we demonstrate that the laminations are rare ferrogenic varves, with an annual deposition pattern comprised of seasonal changes in biogenic production superimposed on seasonal precipitates of iron and manganese hydroxides. The floating μCT-counted varve chronology presented here is the first non-glacial varve chronology in Norway and covers 4023 +113/-185 years. We find that μCT scans allow for a very fast and non-destructive way of counting varves with sufficient detail of varve boundaries. In the few sections where varve boundaries are too vague to resolve, we recommend using complimentary techniques such as thin sections in parallel. The varve chronology is in good agreement with the 95% confidence interval of the independent radiocarbon chronology based on 16 14C dates, and 210Pb and 137Cs activity peaks, indicating that the varve chronology can be equated to calendar age.

• Dijk, Evelien Van; Jungclaus, Johann; Lorenz, Stephan; Timmreck, Claudia & Krüger, Kirstin (2022). Was there a volcanic-induced long-lasting cooling over the Northern Hemisphere in the mid-6th-7th century? Climate of the Past. ISSN 1814-9324. 18(7), p. 1601–1623. doi: 10.5194/cp-18-1601-2022. Full text in Research Archive Show summary

  Abstract. The climate of the Northern Hemisphere (NH) in the mid-6th century was one of the coldest during the last 2 millennia based on multiple paleo-proxies. While the onset of this cold period can be clearly connected to the volcanic eruptions in 536 and 540 Common Era (CE), the duration, extent, and magnitude of the cold period are uncertain. Proxy data are sparse for the first millennium, which compounds the uncertainties of the reconstructions. To better understand the mechanisms of the prolonged cooling, we analyze new transient simulations over the Common Era and enhance the representation of mid-6th to 7th century climate by additional ensemble simulations covering 520–680 CE. We use the Max Planck Institute Earth System Model to apply the external forcing as recommended in the Paleoclimate Modelling Intercomparison Project phase 4. After the four large eruptions in 536, 540, 574, and 626 CE, a significant mean surface climate response in the NH lasting up to 20 years is simulated. The 2 m air temperature shows a cooling over the Arctic in winter, corresponding to the increase in Arctic sea ice, mainly in the Labrador Sea and to the east of Greenland. The increase in sea-ice extent relates to a decrease in the northward ocean heat transport into the Arctic within the first 2 years after the eruptions and to an increase in the Atlantic meridional overturning circulation, which peaks 10 years after the eruptions. A decrease in the global ocean heat content is simulated after the eruptions that does not recover during the simulation period. These ocean–sea-ice interactions sustain the surface cooling, as the cooling lasts longer than is expected solely from the direct effects of the volcanic forcing, and are thus responsible for the multi-decadal surface cooling. In boreal summer, the main cooling occurs over the continents at midlatitudes. A dipole pattern develops with high sea level pressure and a decrease in both precipitation and evaporation poleward of 40∘ N. In addition, more pronounced cooling over land compared to ocean leads to an enhanced land–sea contrast. While our model ensemble simulations show a similar ∼20-year summer cooling over NH land after the eruptions as tree ring reconstructions, a volcanic-induced century-long cooling, as reconstructed from tree ring data, does not occur in our simulations.

• Mjærum, Axel; Loftsgarden, Kjetil & Solheim, Steinar (2022). Human-vegetation dynamics in Holocene south-eastern Norway based on radiocarbon dated charcoal from archaeological excavations. The Holocene. ISSN 0959-6836. 32(7), p. 690–702. doi: 10.1177/09596836221088242. Full text in Research Archive Show summary

  Charcoal from archaeological contexts differs from off-site pollen samples as it is mainly a product of intentional human action. As such, analysis of charcoal from excavations is a valuable addition to studies of past vegetation and the interaction between humans and the environment. In this paper, we use a dataset consisting of 6186 dated tree species samples from 1239 archaeological sites as a proxy to explore parts of the Holocene forest development and human-vegetation dynamics in South-Eastern Norway. From the middle of the Late Neolithic (from c. 2000 BC) throughout the Early Iron Age (to c. AD 550) the region’s agriculture is characterized by fields, pastures and fallow. Based on our data, we argue that these practices, combined with forest management, clearly altered the natural distribution of trees and favoured some species of broadleaved trees. The past distribution of hazel (Corylus avellana) is an example of human impact on the vegetation. Today, hazel is not even among the 15 most common tree species, while it is one of the most prevalent species in the archaeological record before AD 550. The data indicate that this species was favoured already by the region’s Mesolithic hunter-fisher-gatherers, and that it was among the species that thrived extremely well in the early farming landscape. Secondly, our analysis also indicates that spruce (Picea abies) first formed large stands in the south-eastern parts of Norway c. 500 BC, centuries earlier than previously assumed. It is argued that this event, and a further westward expansion of spruce, was partly a consequence of a specific historical event – the first millennium BC farming expansion.

• Bajard, Manon Juliette Andree; Ballo, Eirik Gottschalk; Høeg, Helge Irgens; Bakke, Jostein; Støren, Eivind Wilhelm Nagel & Loftsgarden, Kjetil [Show all 11 contributors for this article] (2022). Climate adaptation of pre-Viking societies. Quaternary Science Reviews. ISSN 0277-3791. 278. doi: 10.1016/j.quascirev.2022.107374. Full text in Research Archive Show summary

  Understanding how the Viking societies were impacted by past climate variability and how they adapted to it has hardly been investigated. Here, we have carried out a new multi-proxy investigation of lake sediments, including geochemical and palynological analyses, to reconstruct past changes in temperature and agricultural practices of pre-Viking and Viking societies in Southeastern Norway during the period between 200 and 1300 CE. The periods 200–300 and 800–1300 CE were warmer than the 300–800 CE period, which is known as the “Dark Ages Cold Period”. This cold period was punctuated by century-scale more temperate intervals, which were dominated by the cultivation of cereals and hemp (before 280 CE, 420–480 CE, 580–700 CE, and after 800 CE). In between, cold intervals were dominated by livestock farming. Our results demonstrate that the pre-Viking societies changed their agricultural strategy in response to climate variability during the Late Antiquity.

• Abbott, Peter; Plunkett, Gill; al, . et & Sigl, Michael (2021). Cryptotephra from the Icelandic Veiðivötn 1477 CE eruption in a Greenland ice core: confirming the dating of volcanic events in the 1450s CE and assessing the eruption's climatic impact. Climate of the Past. ISSN 1814-9324. 17, p. 565–585. doi: 10.5194/cp-17-565-2021. Full text in Research Archive Show summary

  Volcanic eruptions are a key source of climatic variability, and reconstructing their past impact can improve our understanding of the operation of the climate system and increase the accuracy of future climate projections. Two annually resolved and independently dated palaeoarchives – tree rings and polar ice cores – can be used in tandem to assess the timing, strength and climatic impact of volcanic eruptions over the past ∼ 2500 years. The quantification of post-volcanic climate responses, however, has at times been hampered by differences between simulated and observed temperature responses that raised questions regarding the robustness of the chronologies of both archives. While many chronological mismatches have been resolved, the precise timing and climatic impact of two major sulfate-emitting volcanic eruptions during the 1450s CE, including the largest atmospheric sulfate-loading event in the last 700 years, have not been constrained. Here we explore this issue through a combination of tephrochronological evidence and high-resolution ice-core chemistry measurements from a Greenland ice core, the TUNU2013 record. We identify tephra from the historically dated 1477 CE eruption of the Icelandic Veiðivötn–Bárðarbunga volcanic system in direct association with a notable sulfate peak in TUNU2013 attributed to this event, confirming that this peak can be used as a reliable and precise time marker. Using seasonal cycles in several chemical elements and 1477 CE as a fixed chronological point shows that ages of 1453 CE and 1458 CE can be attributed, with high precision, to the start of two other notable sulfate peaks. This confirms the accuracy of a recent Greenland ice-core chronology over the middle to late 15th century and corroborates the findings of recent volcanic reconstructions from Greenland and Antarctica. Overall, this implies that large-scale Northern Hemisphere climatic cooling affecting tree-ring growth in 1453 CE was caused by a Northern Hemisphere volcanic eruption in 1452 or early 1453 CE, and then a Southern Hemisphere eruption, previously assumed to have triggered the cooling, occurred later in 1457 or 1458 CE. The direct attribution of the 1477 CE sulfate peak to the eruption of Veiðivötn, one of the most explosive from Iceland in the last 1200 years, also provides the opportunity to assess the eruption's climatic impact. A tree-ring-based reconstruction of Northern Hemisphere summer temperatures shows a cooling in the aftermath of the eruption of −0.35 ∘C relative to a 1961–1990 CE reference period and −0.1 ∘C relative to the 30-year period around the event, as well as a relatively weak and spatially incoherent climatic response in comparison to the less explosive but longer-lasting Icelandic Eldgjá 939 CE and Laki 1783 CE eruptions. In addition, the Veiðivötn 1477 CE eruption occurred around the inception of the Little Ice Age and could be used as a chronostratigraphic marker to constrain the phasing and spatial variability of climate changes over this transition if it can be traced in more regional palaeoclimatic archives.

• Schure, Anneke Theresia Maria ter; Bajard, Manon Juliette Andree; Loftsgarden, Kjetil; Høeg, Helge Irgens; Ballo, Eirik Gottschalk & Bakke, Jostein [Show all 12 contributors for this article] (2021). Anthropogenic and environmental drivers of vegetation change in southeastern Norway during the Holocene. Quaternary Science Reviews. ISSN 0277-3791. 270. doi: 10.1016/j.quascirev.2021.107175. Full text in Research Archive Show summary

  Uncovering anthropogenic and environmental drivers behind past biological change requires integrated analyses of long-term records from a diversity of disciplines. We applied an interdisciplinary approach exploring effects of human land-use and environmental changes on vegetation dynamics at Lake Ljøgottjern in southeastern Norway during the Holocene. Combined analysis of pollen and sedimentary ancient DNA (sedaDNA) metabarcoding of the sedimentary sequence of the lake describes the vegetation dynamics at different scales, and establishes a timeline for pastoral farming activities. We integrate this reconstruction with geochemical analysis of the sediments, climate data, archaeological evidence of local human settlement and regional human population dynamics. Our data covering the last 10,000 years reveals consistent vegetation signals from pollen and sedaDNA indicating periods of deforestation connected to cultivation, matching the archaeological evidence. Multivariate analysis integrating the environmental data from geochemical and archaeological reconstructions with the vegetation composition indicates that the vegetation dynamics at Lake Ljøgottjern were primarily related to natural processes from the base of the core (in ca. 8000 BCE, Mesolithic) up to the Early Iron Age (ca. 500 BCE–550 CE), when agricultural activities in the region intensified. The pollen signal reflects the establishment of a Bronze Age (ca. 1800–500 BCE) farm in the area, while subsequent intensification of pollen concentrations of cultivated plants combined with the first sedaDNA signals of cultivation and pastoralism are consistent with evidence of the establishment of farming closer to the lake at around 300 BCE. These signals also correspond to the intensification of agriculture in southeastern Norway in the first centuries of the Early Iron Age. Applying an interdisciplinary approach allows us to reconstruct anthropogenic and environmental dynamics, and untangle effects of human land-use and environmental changes on vegetation dynamics in southeastern Norway during the Holocene.

View all works in NVA

• Tjoflot, Gunn Kristin (2025). Editor's highlight of Vikings article about the Eldgjá eruption. https://www.mn.uio.no/geo/. Full text in Research Archive Show summary

  The article "Revisiting the 10th-century Eldgjá eruption: Modeling the climatic and environmental impacts", by Fuglestvedt, H. F. et al is hightlighted by the EOS editor. The article is published in the AGU scientific journal Geophysical Research Letters.

• Tjoflot, Gunn Kristin (2025). Opplev "Den lille istiden": Ei lita, men innhaldsrik utstilling om tilpassingar i førre klimakrise. Titan.uio.no. Full text in Research Archive Show summary

  Korleis opplevde folk i Noreg den vesle istida (ca. 1500–1850) og korleis måtte dei tilpasse seg dei barske forholda? Ny utstilling i Klimahuset på Tøyen.

• Tjoflot, Gunn Kristin (2025). Bidrar til "Vulkanen våkner" i NRKs Katastrofe TV-serie! https://www.mn.uio.no/geo/. Full text in Research Archive Show summary

  Hvor godt forberedt er vi i Norge på den neste katastrofen? NRK og programleder Andreas Wahl har stilt spørsmålet gjennom seks fiktive, men realistiske katastrofescenarioer i TV-serien "Katastrofe". Flere forskere fra Institutt for geofag har deltatt i episode 3 med bakgrunnskunnskap og/eller intervju.

• Loftsgarden, Kjetil (2024). The Iron Age demography – burials as a proxy for exploring population dynamics and the 6th century crisis in Western Scandinavia. Full text in Research Archive
• Krüger, Kirstin & VIKINGS, Team (2024). Highlights from the VIKINGS project (Volcanoes, climate & society). Full text in Research Archive
• Solheim, Steinar & Loftsgarden, Kjetil (2024). The ultimate proxy data? The significant research value of radiocarbon databases. Full text in Research Archive
• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2024). Climate response to the size and season of high-latitude, effusive volcanic eruptions. Full text in Research Archive
• Zoega, Tomas; Storelvmo, Trude & Krüger, Kirstin (2024). Surface climate response to the size and season of northern hemisphere, high latitude, effusive volcanic eruptions. Full text in Research Archive
• Burke, Andrea; Fuglestvedt, Herman Fæhn; Thomas, Liz; Marshall, Lauren & Krüger, Kirstin (2024). Revisiting the ‘transfer function’ of stratospheric sulfur loading from volcanic sulfate deposited on polar ice sheets. Full text in Research Archive
• Fuglestvedt, Herman Fæhn; Burke, Andrea & Krüger, Kirstin (2024). Refining volcanic forcing reconstructions Significance of the eruption season of northern extratropical eruptions. Full text in Research Archive
• Fuglestvedt, Herman Fæhn; Gabriel, Imogen; Sigl, Michael; Thordarson, Thorvaldur & Krüger, Kirstin (2024). Revisiting the 10th century Eldgjá eruption Modelling its climatic and environmental impacts. Full text in Research Archive
• Brodowsky, Christina Victoria; Barker, Simon; Sigl, Michael & Krüger, Kirstin (2024). Climatic and environmental impacts of an Oruanui-like supereruption in the Southern Hemisphere extratropics. Full text in Research Archive Show summary

  Explosive volcanic eruptions have disrupted the climate system dramatically in the past. Recent volcanological fieldwork suggests that at least four VEI 8 events took place in the past 100’000 years, depositing large amounts of volcanic volatiles onto polar ice sheets, each one with potentially significant impacts on human life on Earth. Previous studies on this research topic and time period tend to focus either on tropical eruptions or only consider changes in radiative forcing due to orbital parameters, solar variability, or changes in atmospheric CO2. Here, we seek to evaluate the climatic and environmental impacts of the ~25.5 ka Oruanui eruption (Taupō caldera, 38°S, 175°E, New Zealand). We thereby refine our understanding of the volcanic forcing based on volcanological and ice core data to provide a basis for long-term climate simulations. We use existing emission details for an idealized Oruanui-like eruption scenario. We run an ensemble of CESM2/WACCM simulations with 1850 pre-industrial conditions and instantaneously emit 260 Tg SO2, and the corresponding halogen load derived from petrological estimates into the stratosphere. We then analyze the climatic effects in the decades following the eruption compared with available paleo proxies. Our overarching goal is to provide comprehensive insights into the climatic and environmental repercussions of an Oruanui-like eruption, with a specific emphasis on the differences to tropical events of comparable magnitude. By comparing these two distinct types of eruptions, we aim to contribute to a refined understanding of volcanic impacts on Earth's climate and human life.

• Krüger, Kirstin; Dijk, Evelien Van; Jungclaus, Johann; Sigl, Michael & Timmreck, Claudia (2024). High-frequency climate forcing causes prolonged cold periods in the Holocene. Full text in Research Archive
• Krüger, Kirstin; Fuglestvedt, Herman Fæhn; Gabriel, Imogen; Sigl, Michael & Thordarson, Thorvaldur (2024). Revisiting the 10th-Century Eldgjá Eruption: Modeling the Climatic and Environmental Impacts. Full text in Research Archive Show summary

  The 10th-century Eldgjá eruption in Iceland is the largest basaltic flood lava eruption of the Common Era. However, the extent of its impacts is unclear due to limited historical records. By combining recent tephra analyses in volcanology and ice-core records, we present a gas emissions scenario for the Eldgjá eruption that spans 937 to 940 CE, co-injecting volcanic sulfur and halogens. The combined tropospheric and stratospheric sulfur emissions are 3-8 times higher than those adopted for Eldgjá in existing paleoclimate simulations. Earth system modeling of this scenario under pre-industrial conditions reveals a compound event with maximum northern extratropics surface cooling of ~2°C in summer-autumn of 939 and 940 CE, prolonged Arctic sea ice growth, and large-scale precipitation changes, concurrent with stratospheric ozone depletion and elevated pollution. These results imply that the combined climatic and environmental effects of the Eldgjá eruption may have significantly impacted human populations at the time.

• Krüger, Kirstin; Fuglestvedt, Herman Fæhn; Gabriel, Imogen; Sigl, Michael & Thordarson, Thorvaldur (2024). Revisiting the 10th-Century Eldgjá Eruption: Modeling the Climatic and Environmental Impacts. Full text in Research Archive Show summary

  The 10th-century Eldgjá eruption in Iceland is the largest basaltic flood lava eruption of the Common Era. However, the extent of its impacts is unclear due to limited historical records. By combining recent tephra analyses in volcanology and ice-core records, we present a gas emissions scenario for the Eldgjá eruption that spans 937 to 940 CE, co-injecting volcanic sulfur and halogens. The combined tropospheric and stratospheric sulfur emissions are 3-8 times higher than those adopted for Eldgjá in existing paleoclimate simulations. Earth system modeling of this scenario under pre-industrial conditions reveals a compound event with maximum northern extratropics surface cooling of ~2°C in summer-autumn of 939 and 940 CE, prolonged Arctic Sea ice growth, and large-scale precipitation changes, concurrent with stratospheric ozone depletion and elevated pollution. These results imply that the combined climatic and environmental effects of the Eldgjá eruption may have significantly impacted human populations at the time.

• Krüger, Kirstin (2023). Volcanic eruptions and viking society. [Internet]. https://www.sigma2.no/volcanic-eruptions-and-viking-society. Full text in Research Archive Show summary

  How did volcanic eruptions and their climate impact shape the early history and society of Scandinavia? .... Article is to be read at this link: https://www.sigma2.no/volcanic-eruptions-and-viking-society

• Loftsgarden, Kjetil (2023). Raknehaugen og fimbulvinteren. Full text in Research Archive
• Zanchettin, Davide; Timmreck, Claudia; Kohdri, Myriam; Hegerl, Gabi; Krüger, Kirstin & et, al. (2023). The Model Intercomparison Project on the Climatic Response to Volcanic Forcing (VolMIP): Status and Future Perspectives of the Initiative. Full text in Research Archive Show summary

  The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP) is a protocol-driven international initiative under the umbrella of the sixth phase of the Coupled Model Intercomparison Project (CMIP6) aiming at coordinating the activities of different Research Institutes involved in numerical climate modelling focused on a multi-model assessment of climate models' performance under strong volcanic forcing conditions. The main objective of the initiative is to assess to what extent responses of the coupled ocean-atmosphere system to the same applied strong volcanic forcing are robustly simulated across state-of-the-art coupled climate models and identify the causes that limit robust simulated behavior, especially differences in their treatment of physical processes. To this purpose, four Tier-1 (mandatory) experiments branched into two main sets, named “volc-pinatubo” and “volc-long” were defined, together with eight more lower-priority experiments. Six years since the definition of the VolMIP protocol (Zanchettin et al., 2016), ensemble simulations of most of the mandatory VolMIP experiments have been completed and made publicly available through the Earth System Grid Federation open platform, with the first VolMIP results being currently published and several analyses in progress. The long turnover time between the experiment design, the integration of the simulations and the analysis of the output motivates an assessment of the overall effectiveness of the VolMIP strategy, particularly in the light of a possible second phase of the initiative. In this contribution, we will illustrate the status of the initiative, highlight its major achievements and discuss its future perspective in the light of emergent scientific questions regarding volcanically forced climate variability. Zanchettin, D., Khodri, M., Timmreck, C., Toohey, M., Schmidt, A., Gerber, E. P., Hegerl, G., Robock, A., Pausata, F. S. R., Ball, W. T., Bauer, S. E., Bekki, S., Dhomse, S. S., LeGrande, A. N., Mann, G. W., Marshall, L., Mills, M., Marchand, M., Niemeier, U., Poulain, V., Rozanov, E., Rubino, A., Stenke, A., Tsigaridis, K., and Tummon, F.: The Model Intercomparison Project on the climatic response to Volcanic forcing (VolMIP): experimental design and forcing input data for CMIP6, Geosci. Model Dev., 9, 2701–2719, https://doi.org/10.5194/gmd-9-2701-2016, 2016

• Tjoflot, Gunn Kristin (2023). Volcanic eruptions and the Viking society – The VIKINGS project and use of HPC resources. https://www.mn.uio.no/geo/. Full text in Research Archive Show summary

  The research project VIKINGS is one of the highlighted projects using the Norwegian High-performance computing (HPC) infrastructure SIGMA2 in an annual report for the HPC services. Project leader, Prof Kirstin Krüger has been interviewed in an article about how they use the HPC infrastructure and the research findings so far in the project. infrastrukturen og funn i prosjektet.

• Sigl, Michael; Fuglestvedt, Herman Fæhn; Krüger, Kirstin; Zhuo, Zhihong & et, al. (2023). Solar radiation management from Icelandic volcanoes during the Medieval Quiet Period. Full text in Research Archive
• Svensen, Henrik Hovland (2023). Om vulkanutbrudd og klimakonsekvenser. [Radio]. NRK Radio P2. Full text in Research Archive
• Krüger, Kirstin & VIKINGS, Team (2023). Climatic and societal impacts in Scandinavia following the 536/540 CE volcanic double event. Full text in Research Archive
• Krüger, Kirstin & VIKINGS, Team (2023). Volcanic Eruptions and their Impacts on Climate and Society in 500-1250 CE. Full text in Research Archive
• Krüger, Kirstin (2023). Volcanic eruptions and Viking society. [Internet]. Sigma2. Full text in Research Archive Show summary

  Volcanic eruptions and the Viking society – The VIKINGS project and use of HPC resources

• Krüger, Kirstin & et, al. (2023). Initial meteorological conditions and eruption source parameters’ control on volcanic forcing and response. Full text in Research Archive
• Krüger, Kirstin & VIKINGS, Team (2023). VIKINGS: Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 Common Era. Full text in Research Archive
• Fuglestvedt, Herman Fæhn; Zhuo, Zhihong; Toohey, Matthew & Krüger, Kirstin (2023). Arctic Polar Vortex Controls Aerosol Evolution After High-Latitude Volcanic Eruptions. Full text in Research Archive
• Fuglestvedt, Herman Fæhn; Gabriel, Imogen; Hutchison, William; Plunkett, Gill; Burke, Andrea & Sigl, Michael [Show all 8 contributors for this article] (2023). Impacts of the Icelandic Eldgjá eruption in 937-940 CE. Full text in Research Archive
• Gundersen, Ingar Mørkestøl (2022). Iron Age Vulnerability. An analytical approach to the Fimbulwinter hypothesis. Full text in Research Archive
• Ballo, Eirik Gottschalk (2022). Lipid biomarkers in Lake Sagtjernet, Norway. Full text in Research Archive
• Boessenkool, Sanne (2022). Unearthing past ecologies and societies using sedimentary ancient DNA. Full text in Research Archive
• Fuglestvedt, Herman Fæhn (2022). Arctic Polar Vortex Controls Aerosol Evolution After High-Latitude Volcanic Eruptions. Full text in Research Archive
• Fuglestvedt, Herman Fæhn (2022). High-Latitude Explosive Volcanic Eruptions and Their Sensitivity to Source Parameters. Full text in Research Archive
• Ballo, Eirik Gottschalk; Bajard, Manon Juliette Andree; Bakke, Jostein; Støren, Eivind Wilhelm Nagel; D'Andrea, William J. & Høeg, Helge Irgens (2022). Lake Sagtjernet hydrogen isotopes and pollen. Full text in Research Archive
• Sigl, Michael; Gabriel, Imogen & Krüger, Kirstin (2022). Timing of Holocene volcanic eruptions and their radiative aerosol forcing. Full text in Research Archive
• Gabriel, Imogen & Sigl, Michael (2022). Insight into volcano-climate impacts between 750 and 770 CE using the Greenland ice core records. Full text in Research Archive
• Gabriel, Imogen & Sigl, Michael (2022). Deciphering the sources and climate impact potential of pre-historic volcanic eruptions from Iceland using the Greenland ice cores: a case study from the 8th century. Full text in Research Archive
• Bajard, Manon Juliette Andree (2022). Agricultural and climatic contexts associated to the Fimbulwinter in the area of Gardermoen: when pre-Viking societies adapted to the climate. Full text in Research Archive
• Hutchinson, William & Sigl, Michael (2022). Timing and climate impact of Iceland’s largest basaltic eruptions: new insights from ice core archives. Full text in Research Archive
• Krüger, Kirstin; Fuglestvedt, Herman Fæhn; Dijk, Evelien Van; Zhuo, Zhihong; Sigl, Michael & Toohey, Matthew (2022). Modelling volcanic climate and environmental impacts and their signals in ice cores. Full text in Research Archive
• Krüger, Kirstin; Fuglestvedt, Herman Fæhn; Zhuo, Zhihong; Mills, Mike & Sigl, Michael (2022). Volcanic sulfate deposition to Greenland and Antarctica: A modeling sensitivity study with CESM(WACCM). Full text in Research Archive Show summary

  Reconstructions of the atmospheric sulfate aerosol burdens resulting from past volcanic eruptions are based on ice core-derived estimates of volcanic sulfate deposition and the assumption that the two quantities are directly proportional. Toohey et al (2013) modelled that the Antarctic and Greenland volcanic sulfate deposition is nonlinear for very large sulfur rich tropical eruptions (Tambora magnitude and larger), with significantly less sulfate deposition to Antarctica than to Greenland using the MAECHAM5-HAM aerosol-climate model. Here we test the relationship for simulations of explosive tropical and extratropical Northern Hemisphere volcanic eruptions by co-injecting sulfur and halogens into the stratosphere with the CESM2(WACCM) model including aerosol, chemistry, climate, and earth system processes. We consider different eruption parameters varying composition, latitude, season, injection height and magnitude. We run the model injecting 17 Tg and 200 Tg of SO2, together with scaled halogens, at 24 km altitude 15° N and 64° N during January and July pre industrial 1850 conditions. We will analyse the modelled sulphate deposition signals over Greenland and Antarctica and compare them to the volcanic ice core records of known eruptions of comparable strength during the Common Era and the Holocene. The analysis will focus on the deposition fluxes and their Greenland/Antarctica efficiencies in relation to the eruption parameters, sulphate aerosol transport, and the atmospheric circulation and deposition. With the help of the model data we will learn more about the volcanic sources to the sink processes, which will be helpful to better interpret volcanic signals in bipolar ice core records.

• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthew & Krüger, Kirstin (2022). Impacts of tropical versus extratropical volcanic eruptions with sulphur and halogen injections to the stratosphere. Full text in Research Archive
• Krüger, Kirstin (2022). VIKINGS: Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 Common Era. Full text in Research Archive Show summary

  Welcome to the Geo-Wednesday in March! This month Kirstin Krüger, Professor at Meteorology and Oceanography, will give a talk about VIKINGS. VIKINGS is a multi-disciplinary project that aims to understand the role of volcanic eruptions and climate change in shaping the early history of Scandinavia. The period 500-1250 Common Era 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, and especially in Scandinavia during this period, are however poorly resolved even on a timescale of centuries. Moreover, available dating of archeological findings from the time period have hardly been interpreted within a framework of climatic and environmental change. The VIKINGS project seeks to unravel the climate of this intriguing historic period and to address the role of volcanic eruptions impacting environmental and societal changes with a special focus on Southern Norway. Kirstin Krüger is a Professor in Meteorology at the UiO Department of Geosciences and the leader of the VIKINGS project – a Norwegian TOPPFORSK project. Her research focuses on stratospheric dynamics and the role of transport from climate relevant gases from the surface to the middle atmosphere. In the past 15 years, she has worked on large explosive volcanic eruptions and their impacts on climate, environment and society during present day and paleo time scales.

• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthew; Mills, Michael J & Krüger, Kirstin (2022). Impacts of tropical versus extratropical volcanic eruptions co-injecting sulphur and halogen to the stratosphere. Full text in Research Archive
• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn & Krüger, Kirstin (2022). Impacts of tropical versus extratropical volcanic eruptions co-injecting sulfur and halogen to the stratosphere. Full text in Research Archive
• Hutchison, William; Krüger, Kirstin & et, al (2022). Timing and climate impact of Iceland’s largest basaltic eruptions: new insights from ice core archives. Full text in Research Archive
• Loftsgarden, Kjetil (2022). The wonderful 7th century. Full text in Research Archive
• Krüger, Kirstin & et, al (2022). Volcanic sulfate deposition to Greenland and Antarctica: A modeling sensitivity study with CESM(WACCM). Full text in Research Archive
• Krüger, Kirstin; Brenna, Hans & et, al (2022). How large has a volcanic eruption to be to disrupt the QBO? Full text in Research Archive Show summary

  The dominating circulation phenomenon in the tropical stratosphere is the quasi-biennial oscillation (QBO), an approximately 28 months oscillation of alternating easterly or westerly winds centered at the equator. Volcanic aerosols may have an impact on the QBO phase as was observed for the Pinatubo eruption, which showed a “remarkably” prolonged Easterly wind regime. In contrast, geo-engineering studies model a prolonged Westerly phase or a shut-down of the QBO due to the artificial injection of sulfate aerosols. Extremely large volcanic eruptions which inject several 10s to 100s Tg SO2 might therefore have the potential to disturb the QBO. In addition, recent observations revealed two anomalous disruptions of the QBO in the 2010s with anomalous westerly winds probably due to Rossby wave propagating from the extratropics. We use an Earth System Model taking volcanic aerosol chemistry climate interactions into account to study the QBO response to violent volcanic eruptions. Simulating a tropical supereruption with 1000 Tg SO2 and halogens injection into the stratosphere reveals a disruption of the QBO for up to 10 years first with anomalous Easterlies followed by anomalous Westerlies before returning to a QBO regime with slightly longer period. Volcanic aerosol heating and ozone depletion cooling lead to the QBO disruption and anomalous wind regimes through radiation and wave-mean flow interactions. Here, we present a new set of sulfur- and halogen-rich volcanic eruptions experiments with 17 and 200 Tg SO2 injections into the tropical and Northern Hemisphere extratropics during January and July season to answer the above raised question.

• Fuglestvedt, Herman Fæhn; Zhuo, Zhihong; Mills, Michael J. & Krüger, Kirstin (2021). Modelling the atmospheric impacts of high-latitude explosive volcanic eruptions. Full text in Research Archive
• Fuglestvedt, Herman Fæhn; Zhuo, Zhihong; Michael, Mills & Krüger, Kirstin (2021). Modelling the atmospheric impacts of high-latitude explosive volcanic eruptions. Full text in Research Archive
• Dijk, Evelien Van; Gundersen, Ingar Mørkestøl; Loftsgarden, Kjetil; Krüger, Kirstin & Iversen, Frode (2021). Can we link volcanic impacts on the climate to a change in society in Norway? Full text in Research Archive
• Dijk, Evelien Van & Krüger, Kirstin (2021). Large volcanic eruptions as a natural hazard: The impact of the 536/540 CE double event on the atmospheric circulation, surface climate, vegetation and society in Scandinavia. Full text in Research Archive
• Dijk, Evelien Van; Gundersen, Ingar Mørkestøl; Loftsgarden, Kjetil; Ballo, Eirik Gottschalk; Krüger, Kirstin & Iversen, Frode (2021). Can we link volcanic impacts on the climate to a change in society? Full text in Research Archive
• Dijk, Evelien Van & Krüger, Kirstin (2021). Impact of large volcanic eruptions on the 6th-7th century climate. Full text in Research Archive
• Fuglestvedt, Herman; Krüger, Kirstin; Zhuo, Zhihong; Sigl, Michael; Toohey, Matthew & Mills, Michael J. (2021). Modelling high-latitude explosive eruptions and their atmospheric and environmental impacts. Full text in Research Archive
• Zhuo, Zhihong; Fuglestvedt, Herman; Toohey, Matthew; Mills, Michael J. & Krüger, Kirstin (2021). Model comparison of volcanic aerosol forcing and climate impact of tropical and extratropical eruptions. Full text in Research Archive
• Schure, Anneke ter; Bajard, Manon Julietto Andree; Loftsgarden, Kjetil; Høeg, Helge Irgens; Ballo, Eirik Magnus Gottschalk & Bakke, Jostein [Show all 12 contributors for this article] (2021). Disentangling anthropogenic and environmental drivers of biological change in southeastern Norway during the Holocene. Full text in Research Archive
• Schure, Anneke ter; Bajard, Manon Julietto Andree; Loftsgarden, Kjetil; Høeg, Helge Irgens; Ballo, Eirik Magnus Gottschalk & Bakke, Jostein [Show all 12 contributors for this article] (2021). Anthropogenic and environmental drivers of biological change in southeastern Norway during the Holocene. Full text in Research Archive
• Bajard, Manon Julietto Andree; Ballo, Eirik Magnus Gottschalk; Høeg, Helge I.; Bakke, Jostein; Støren, Eivind N. & Loftsgarden, Kjetil [Show all 11 contributors for this article] (2021). Instability or adaptation of the pre-Viking society to the climate variability of the Late Antiquity? Full text in Research Archive Show summary

  Understanding how agricultural societies were impacted and adapted to past climate variations is critical to adapt to contemporary climate change and guaranty the food security. However, linking climate and change in the behaviour of a population are difficult to evidence. Here, we studied the climate variations of the period between 200 and 1300 CE and its impact on the pre-Viking and Viking societies in south Norway. We used a retrospective approach combining a multi-proxy analysis of lake sediments, including geochemical and palynological analyses, to reconstruct past changes in temperature and agricultural practices during the period 200-1300 CE. We associated variations in Ca/Ti ratio as a result of change in lake productivity with the temperature. The periods 200-300 and 800-1300 CE were warmer than the period between 300 and 800 CE, which is known as the “Dark Ages Cold Period” in the Northern Hemisphere. During this colder period, phases dominated by grazing activities (280-420 CE, 480-580 CE, 700-780 CE) alternated with phases dominated by the cultivation of cereals and hemp (before 280 CE, 420-480 CE, 580-700 CE, and after 800 CE). The alternation of these phases is synchronous of temperature changes. Cold periods are associated to livestock farming, and warmer periods to crop farming. This result suggests that when temperature no longer allowed crop farming, the food production specialized in animal breeding. The development of activities reached a maximum between 400 and 550 CE and a minimum between 680 and 800 CE, in agreement with archaeological findings. The Viking Age (800-1000 CE) started with an increase in temperature and corresponds to the warmest period between 200 and 1300 CE, allowing a larger development of the agriculture practices and society. Our results prove that the pre-Viking society adapted their agricultural practices to the climate variability of the Late Antiquity and that the Vikings expanded with climate warming.

• Sigl, Michael (2021). Volcanism & Climate during the past 2,500 years; Joint seminar in atmospheric, ocean and climate science. Full text in Research Archive
• Gabriel, Imogen & Sigl, Michael (2021). Tephra in the Greenland Ice cores: Insights into Icelandic volcano-climate impacts. Full text in Research Archive
• Gabriel, Imogen & Sigl, Michael (2021). Unlocking the secrets of past Icelandic volcanism with tephra. Full text in Research Archive
• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn & Krüger, Kirstin (2021). Impacts of tropical versus extratropical volcanic eruptions (including volcanic sulphur and halogen injections). Full text in Research Archive
• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthew; Mills, Michael J. & Krüger, Kirstin (2021). Model comparison of stratospheric aerosol forcing of tropical and extratropi-cal volcanic eruptions. Full text in Research Archive Show summary

  Major volcanic eruptions, as one of the natural forcing, increase sulfate aerosols in the stratosphere. The stratospheric aerosol forcing differs from tropical and extratropical eruptions, and depends on the eruption season and height, and volcanic volatile injections. In order to study different aerosol forcing and their impact, we perform simulations based on the fully coupled Community Earth System Model version 2 (CESM2) with the Whole Atmosphere Community Climate Model version 6 (WACCM6) with prognostic stratospheric aerosol and chemistry. Explosive eruptions at 14.6 N and 63.6 N in January and July injecting 17 Tg and 200 Tg SO2 at 24 km with and without halogens are simulated, in line with Central American Volcanic Arc and Icelandic volcanic eruptions. Simulated changes in the stratospheric sulfate and halogen burdens, and impacts on aerosol optical depth and ozone are analyzed.

• Zhuo, Zhihong; Fuglestvedt, Herman Fæhn; Toohey, Matthew; Mills, Michael J. & Krüger, Kirstin (2021). Model comparison of aerosol forcing and impactof tropicaland extratropical eruptions. Full text in Research Archive
• Sigl, Michael; Krüger, Kirstin & al, More authors Et (2021). Insights on the timing, global sulfate lifecycle an􀀀 climate impact of Earth's largest (pre-) historic volcanic eruptions. EGU General Assembly. EGU21-946. doi: 10.5194/egusphere-egu21-946,2021. Full text in Research Archive Show summary

  Extratropical volcanic eruptions are commonly thought to be less effective at driving large-scale surface cooling than tropical eruptions, and only the latter are commonly thought to be able to distribute sulfate globally. Here, we test both of these assumptions using a network of ice cores from the polar regions of Antarctica and Greenland covering the past 15’000 years and climate-aerosol modeling. We employ state-of-the-art analyses of trace elements, cryptoptephra and sulphur isotopes (Burke et al., 2019) to gain new insights into the timing of past eruptions, their stratospheric sulphur mass injections and subsequent sulphate aerosol lifecycle. We use this information to estimate the climate impact potential due to negative radiative forcing caused by Earth’s largest volcanic eruptions since the last Glacial. Our analysis encompasses over 1’000 eruptions and include the caldera-forming eruptions of Okmok II (Alaska, 43 BCE, VEI=6, 53°N; McConnell et al., 2020), Aniakchak II (Alaska, 1600s BCE, VEI=6, 57°N), Crater Lake (Mazama, Oregon, 5600s BCE, VEI=7, 43°N) and Laacher See (Germany, c. 13 ka BP, VEI=6, 50°N). We use our reconstructed radiative forcing and the coupled earth system models MPI-ESM1.2 and CESM (version 1.2.2) to analyze the climatic impact caused by these eruptions and compare the simulated temperature response with temperature reconstructions based on ultra-long tree-ring chronologies. Finally, based on these comparisons, we propose a number of stratigraphic age tie-points to anchor ice-core chronologies from Greenland (GICC05) and Antarctica (WD2014) to the absolute dated tree-ring chronology. We thereby aim to improve proxy synchronization throughout the Holocene -- a prerequisite for detection and attribution studies -- and invite the paleo-climate community to update climate proxy records based on ice cores to the latest chronologies. The European Research Council Grant 820047 under the European Union’s Horizon 2020 research and innovation program funded the research project THERA - Timing of Holocene Volcanic eruptions and their radiative aerosol forcing.

• Krüger, Kirstin & VIKINGS, Team (2021). VIKINGS: Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500-1250 Common Era. Full text in Research Archive
• Bajard, Manon Juliette Andree (2021). PC1. Improving food security: new techniques. [Internet]. Press conference/EGU General Assembly 2021. Full text in Research Archive Show summary

  "In 2019, nearly 750 million people were exposed to severe levels of food insecurity. Conservative estimates indicate that more than 3 billion people can’t afford healthy diets, and that the social costs of greenhouse gas emissions associated with current food-consumption patterns will top $1.7 trillion per year within the next decade. This press conference will introduce journalists to some of the latest geoscience research being conducted to help improve global food security, including two types of forecasting that support early warnings in Africa. Additional research strives to improve agricultural management strategies with respect to greenhouse gas emissions and to balance food and water security in cities. Lastly, we will hear how one group of scientists is researching how pre-Viking and Viking societies adapted their agricultural practices to a changing climate to glean fresh insights into how we can improve our future food security." (EGU: 2021)

• Bajard, Manon Juliette Andree & Dacey, James (2021). Food Security Lessons from the Vikings. [Journal]. EOS Science News by AGU. Full text in Research Archive Show summary

  Scandinavian societies of the first millennium adapted their farming practices to volcano-driven climate changes.

• Ballo, Eirik Gottschalk; Bajard, Manon Juliette Andree; Bakke, Jostein & Støren, Eivind Wilhelm Nagel (2021). Using CT scans to count varves: Application to Lake Sagtjernet. Full text in Research Archive
• Krüger, Kirstin (2020). Volcanic Eruptins and their Impacts on Climate, Environment, and Viking Society in 500-1250 CE. Full text in Research Archive Show summary

  This multi-disciplinary project aims to understand the role of volcanic eruptions and climate change in shaping the early history of Europe. The period 500-1250 CE is characterized by natural disasters, societal unrest, Viking expansion, emerging kingship – and large volcanic eruptions evidenced by geochemical markers in natural archives. Contemporary reports of a mysterious cloud which dimmed the light of the sun for at least a year were written at the dawn of the Middle Ages which marked the beginning of an unusual cold period in the mid of the 6th century due to the double volcanic eruption event in 536/540 CE. The social structure of Scandinavian society was radically changed between 500 and 750 CE. Population levels were reduced by plague and agriculture had to be adapted to a colder climate. Tree ring and climate model data from Scandinavia identify a prolonged period of cooling which may have lasted over a century. Following is a period of volcanic activity which was thought to be more quiescent in a global sense and is marked by the onset of the medieval warm period (c. 950 -1250 CE). However, volcanic eruptions in Iceland were frequently active during 700 to 1100 CE and must have had severe impacts on climate, environment and society in Northern Europe, which is not supported by available records. This presentation aims to shed more light into the background of this early Common Era period based on revised volcanic forcing, complex earth system climate model, proxy, and archaeology data.

• Dijk, Evelien Van & Krüger, Kirstin (2020). Was there a volcanic induced long lasting cooling in the mid 6th-7th century? Full text in Research Archive
• Dijk, Evelien Jacoba Cornelia Van & Krüger, Kirstin (2020). Impact of the 536/540 CE double volcanic eruption event on the 6th-7th century climate using model and proxy data. Full text in Research Archive
• Dijk, Evelien Jacoba Cornelia Van & Krüger, Kirstin (2020). The impact of the 536/540 CE double volcanic eruption event on the climate. Full text in Research Archive
• Dijk, Evelien Jacoba Cornelia Van & Krüger, Kirstin (2020). Impact of the 536/540 CE double eruption event on the 6th -7th century climate using model and proxy data. Full text in Research Archive
• Smedsrud, Morten Skipenes & Loftsgarden, Kjetil (2020). Finner tegn til ekte fimbulvinter. [Journal]. Apollon. Full text in Research Archive
• Loftsgarden, Kjetil (2020). The population of Western Scandinavia 400–1000 AD. Full text in Research Archive
• Loftsgarden, Kjetil (2020). Ferd og frakt over fjell og vidde. Forskning.no. ISSN 1891-635X. Full text in Research Archive
• Loftsgarden, Kjetil (2020). How many Vikings were there? The population of Western Scandinavia 400–1000. Full text in Research Archive
• Gundersen, Ingar Mørkestøl (2022). Iron Age Vulnerability. The Fimbulwinter hypothesis and the archaeology of the inlands of eastern Norway. Universitetet i Oslo. Full text in Research Archive Show summary

  A growing body of climate data points towards a significant climate cooling in the northern hemisphere during the 6th century AD. Linked to multiple explosive volcanic eruptions between AD 536-547, the cooling event is the coldest that has been documented for the last 2000 years and seems to have persisted, to varying degrees, well into the latter half of the 6th century. Several researchers have claimed that the 6th-century cooling must have resulted in extensive crop failure throughout Scandinavia, followed by famine, plagues, and social unrest. One hypothesis suggests that the population of the Scandinavian Peninsula may have been halved as a result. The combination of prolonged cooling and presumed crop failure is often compared to Norse myths about the Fimbulwinter, but critics argue that the Fimbulwinter hypothesis is rife with the uncritical use of climate data, a lack of source criticism and deterministic conclusions. In many ways, the ongoing discourse follows in line with previous discourses in archaeology, revolving around an artificial dichotomy between crisis and continuity. In this thesis, I examine the climatic and archaeological premises for the Fimbulwinter hypothesis and discuss it against developing theoretical frameworks within the environmental humanities. By using vulnerability and resilience as analytical tools, the subsistence and settlement patterns of selected landscapes are analysed against the possibility of crop failure and famine, with emphasis on the Gudbrandsdalen valley and the Lake Mjøsa region in the inlands of eastern Norway. I conclude that climate cooling had the potential to critically impact some areas, while others were seemingly less affected. These results suggest significant regional diversity in the consequences and adaptations in relation to the 6th-century cooling event. The hypothesis of a halving of the population is up for revision, but the crisis narrative still cannot be fully discounted. This thesis is also available in the Zenodo archive: https://doi.org/10.5281/zenodo.5782896

View all works in NVA