Understanding climate variability across these 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.
The team of researchers from Norway, Switzerland, and Germany was on the way to study the climate in the late-Holocene with another project in mind. Co-author of the study Kirstin Krüger explains:
“In a project starting back in 2018, we aimed to reveal what impacts volcanic eruptions had on climate and environment, affecting the Viking society in 500–1250 Common Era (CE). In the project named in short VIKINGS, we were particularly interested in two volcanic eruptions affecting people in Scandinavia and Europe, the double eruption-event 536 CE and 540 CE, and how the 6th to mid-7th century was different from the Little Ice Age (LIA, c. 1450-1850) the latest known cold period. We later broadened the time period and area to also go back to 6000 BCE covering the Northern Hemisphere”, says Kirstin Krüger, Professor in meteorology at University of Oslo especially interested in volcanic eruptions impact on climate and environment.
The new study was just published online 8 of May 2024 in the open access journal Communications Earth & Environment, and it gives new insights in amplitudes and trends of climate variations and its drivers throughout most of the Holocene.
“Existing global reconstructions of Holocene temperatures are not able to resolve climate variations at these critical timescales because of the coarse age resolution of the underlying climate archives, their imprecise dating, and other spatial and seasonal biases that arise from compiling different proxy records over such long timescales”, says Michael Sigl, co-author, and Assistant Professor in paleo volcanism and climate impacts at University of Bern.
With use of Earth System Model (ESM) simulations of the mid- to late-Holocene, forced by reconstructions of external climate forcing (including the volcanic forcing based on polar ice-core sulphate records), the research team found that eleven long-lasting cold periods occurred in the Northern Hemisphere during the past 8000 years. Researcher Claudia Timmreck and Johan Jungclaus contributed the Max-Planck-Institute (MPI) ESM simulations to this work.
Contrary to what global paleo proxy reconstructions suggest, the study shows that the mid to late-Holocene was not a period of climate stability, but instead was interrupted by Little Ice Age like cold periods. The 11 long-lasting cold periods correlate with enhanced volcanic activity (see figure), where the clustering of volcanic eruptions induced a prolonged surface cooling effect caused by sulphuric acid droplets in the atmosphere from the volcanic eruptions. This led to gradual feedback effects through sea-ice growth and changes in the ocean heat content amplifying the initial cooling effect.
This study challenges the prevailing notion of the Holocene as a period characterized by climate stability, as portrayed in multi-proxy climate reconstructions. Instead, it provides an improved representation of amplitude and timing of temperature variations on sub-centennial timescales which is key to advance studies focusing on the role of climate variations for ancient human societies, conclude the researchers.
The main author of the article was Evelien Van Dijk, a Doctoral Research Fellow at Department of Geoscinces, University of Oslo, Norway.
Figure:
This figure is available in a larger version (1600px): Figure of Northern Hemisphere annual mean surface air temperature anomaly (Relative to 1750-1850 CE). Figure: van Dijk et al 2024.
Contact persons:
Professor Kirstin Krüger, Department of Geosciences, University of Oslo, Norway.
Project leader of the VIKINGS project.
Contact info | Phone: + 47 98234664
Assistant Professor Michael Sigl, Physics Institute and Oeschger Center for Climate Change Research, University of Bern, Bern, Switzerland;
Contact info | Phone: +41 31 684 8652
Dr. Claudia Timmreck, Max-Planck-Institute for Meteorology, Hamburg, Germany:
Contact info | Phone: +49 40 41173-384
Reference to the scientific article:
van Dijk, E.J.C., Jungclaus, J., Sigl, M. et al. High-frequency climate forcing causes prolonged cold periods in the Holocene. Commun Earth Environ 5, 242 (2024). https://doi.org/10.1038/s43247-024-01380-0
Additional information:
About the research project: Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500–1250 CE (VIKINGS), see webpages: https://www.mn.uio.no/geo/english/research/projects/vikings/
Acknowledgement:
This study was funded by the Research Council of Norway and University of Oslo as a Ground-breaking research (FRIPRO) project: Volcanic Eruptions and their Impacts on Climate, Environment, and Viking Society in 500–1250 CE (VIKINGS)
This study was co-funded by the European Research Council (ERC) as part of the European Union's Horizon 2020 research and innovation program (THERA project 820047).
References:
Kaufman, D., McKay, N., Routson, C. et al. Holocene global mean surface temperature, a multi-method reconstruction approach. Sci Data 7, 201 (2020). https://doi.org/10.1038/s41597-020-0530-7
Sigl, M., Toohey, M., McConnell, J. R., Cole-Dai, J., and Severi, M.: Volcanic stratospheric sulfur injections and aerosol optical depth during the Holocene (past 11 500 years) from a bipolar ice-core array, Earth Syst. Sci. Data, 14, 3167–3196, https://doi.org/10.5194/essd-14-3167-2022, 2022.