Cooling and societal change during the Late Antique Little Ice Age from 536 to around 660 AD

Abstract

The supposed role of climate change on societal reorganizations in Europe 1,2 and Asia 3,4 during the first half Common Era (CE) is difficult to prove without adequate annually resolved and absolutely dated climate proxy archives 5,6. Interpretation of concurrences between cooling in the 6 th century and pandemic 7,8 , rising and falling civilizations 1-6 , human migrations and political turmoil 8-13 lacks understanding of scalar and causal mechanisms. Here we use tree-ring chronologies from the Russian Altai and Austrian Alps to reconstruct summer temperatures over the past two millennia. In both regions, conditions during Roman and recent times were warmer than throughout the medieval period. Unprecedented, long-lasting and spatially synchronized cooling following a cluster of large volcanic eruptions in 536, 540 and 547 CE 14 , was likely sustained by ocean and sea-ice feedbacks 15,16 , superimposed on a solar minimum 17. This newly defined Late Antique Little Ice Age (LALIA, 536 to ~660 CE) exceeded the LIA in severity. Covering much of the Northern Hemisphere, it should be considered as an additional environmental factor contributing to the establishment of the Justinian plague 7,8 , transformation of the eastern Roman and collapse of the Sasanian Empire 1,2,5 , movements out of the Asian steppe and Arabian Peninsula 8,11,12 , spread of Slavic-speaking people 9,10 , and upheavals in China 13. Annually resolved and absolutely dated insight into late Holocene climate variability is crucial in order to distinguish anthropogenic from natural forced variation 18 , and to evaluate the performance of climate model simulations 19. Spatially well-distributed palaeoclimatic archives are also essential for answering questions surrounding possible relationships between climate variability and human history 5,6. However, around the world today, there are only 13 temperature sensitive tree-ring chronologies that span the entire CE (Table S1).

An 800 year high-resolution black carbon ice-core record from Lomonosovfonna, Svalbard

“…According to the dust proxy records from the Dasuopu ice core (Tibet), this decade experienced the driest conditions of the last millennium for this part of the globe (Thompson et al, 2000). In the Altai region 9 out of 10 years between 1783 and 1792 belonged to the 10 % of the 35 coldest years of the time period 1200-1850, while following summers between 1793 and 1811 were clearly warmer (Büntgen et al, 2016). Those cold and dry conditions likely promoted dry dead wood accumulation, which then facilitated fire spread when temperatures rose later in the 1790s, a situation in agreement with the findings from Eichler et al (2011).…”

Relationship between solar activity and Δ14C peaks in AD 775, AD 994, and 660 BC

“…Data from high-latitude Siberian and Altai (Jull et al 2014;Büntgen et al 2016) record the AD 775 peak but show a Δ 14 C rise beginning one year earlier, and Δ 14 C data in New Zealand kauri (Güttler et al 2015) indicate a peak delayed by half a year.…”

Evaluating the link between the sulfur-rich Laacher See volcanic eruption and the Younger Dryas climate anomaly

“…Lipid biomarker hydrogen isotope ratios from Meerfelder Maar further corroborate that GS-1 atmospheric cooling began at 12.880 ka BP, coincident with the Laacher See Tephra within the same sediment but preceding the larger dynamical atmospheric response associated with the YD in central Europe by ∼ 170 years (Rach et al, 2014). Aerosol-induced cooling immediately following the eruption may have caused a positive feedback involving sea ice expansion and/or AMOC weakening, as previously proposed for other Greenland stadials over the interval 30-80 ka BP (Baldini et al, 2015a), the 6th century AD (Buntgen et al, 2016), the Little Ice Age (Zhong et al, 2011;Miller et al, 2012), and the Holocene in general (Kobashi et al, 2017). Viewed from this perspective, the YD was simply the latest, and last, manifestation of a last glacial stadial.…”

“…horizontal subpolar gyre circulation; Moreno-Chamarro et al, 2017) changes, although this requires further research to confirm. Large volcanic eruptions in AD 536, 540, and 547 are hypothesised to have triggered a coupled sea-ice-ocean circulation feedback that led to an extended cold period (Buntgen et al, 2016). Recent research also highlights the possibility that volcanism followed by a coupled sea-ice-ocean circulation positive feedback triggered hemispheric-wide centennial-to millennial-scale variability during the Holocene (Kobashi et al, 2017).…”