Was there a volcanic-induced long-lasting cooling over the Northern Hemisphere in the mid-6th–7th century?

Abstract

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.

The impact of volcanism on Scandinavian climate and human societies during the Holocene: Insights into the Fimbulwinter eruptions (536/540 AD)

“…Most climate models confirm cooling effects following Northern Hemisphere volcanic eruptions, aligning with our dynamically downscaled iLOVECLIM model ensemble setup, which reveals surface cooling during the fimbulwinter in Scandinavia. Recent work by van Dijk et al (2022) utilizing the Max Planck Institute Earth System Model and identical PMIP4 volcanic forcing as our study, demonstrates significant cooling in mean Northern Hemisphere surface climate for up to two decades post the major eruptions of 536, 540, 574, and 626 AD. Earlier research on volcanic eruption effects within the last millenium, such as Timmreck et al (2009) and Guillet et al (2020), indicated a decade-long cooling period following exceptionally large eruptions.…”

“…Archeological research into mid-sixth century Scandinavia increasingly links the periods' significant settlement abandonment, reorganization, and material transformation with a brief and abrupt cooling event which followed an explosive volcanic event between 536 and 540 AD (Axboe, 2001;Gräslund, 2007;Gräslund and Price, 2012;Guillet et al, 2020;Gundersen, 1970;Herschend, 2009;Löwenborg, 2023;Price and Gräslund, 2015;Sigl et al, 2013;Toohey et al, 2016;van Dijk et al, 2023;Zachrisson, 2011). The connection to volcanism is established through historical research on known volcanic eruptions before 630 AD (e.g.…”

Roman Warm Period and Late Antique Little Ice Age in an Earth System Model Large Ensemble

“…Numerous previous modeling studies have found and confirmed that volcanic eruptions dominated hemispheric temperature changes over the second millennium of the CE (Brönnimann et al., 2019; Crowley, 2000; Hegerl et al., 2003; Schneider et al., 2009; Schurer et al., 2014). Furthermore, the prominent role of volcanic eruptions in the sixth‐century temperature was confirmed by climate model simulations (Toohey, Stevens, et al., 2016; van Dijk et al., 2022). However, the significant relationship between the solar activity and the NH temperature variability from the proxy data reconstructions (Connolly et al., 2021) is not supported by the climate model simulations over the second millennium of the CE (Schurer et al., 2014) and the Sun's total energy output measurement over the past 30 years (Foukal et al., 2006).…”

The Role of Small to Moderate Volcanic Eruptions in the Early 19th Century Climate

“…Three experiments from 1791 to 1830 are conducted in this study: Large-Only, Small-Included, and No-Volcano. The Large-Only experiment has the same setting as the MPI-ESM CMIP6/PMIP4 past2k simulation (van Dijk et al, 2022) and uses the EVA forcing for the aerosol optical properties from strong eruptions (Figure 1b). The Small-Included experiment changes the volcano forcing to eVolv2k plus D4i (Figure 1b), which includes the small-to-moderate volcanic eruptions as described in Section 2.2 and Supporting Information S1.…”