New article in Nature Geoscience, Fredrik Charpentier Ljungqvist (Dept. of History) and Paul. J. Krusic (Dept. of Physical Geography) among the authors

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New article “Cooling and societal change during the Late Antique Little Ice Age from 536 to around 660 AD” published in Nature Geoscience with Bolin Centre scientists Fredrik Charpentier Ljungqvist (Department of History) and Paul. J. Krusic (Department of Physical Geography) among the authors.

New research suggests links between a century-long deep freeze across Europe and central Asia with famine, large-scale migration, a plague pandemic that ripped through the Eastern Roman Empire, and the expansion of the Arab Empire. Researchers from the international Past Global Changes (PAGES) 2k project write in the journal Nature Geoscience that they have identified an unprecedented, long-lasting cooling in the Northern Hemisphere about 1500 years ago. The drop in temperature immediately followed three large volcanic eruptions in quick succession in the years 536, 540 and 547 AD.

Volcanoes can cause climate cooling by ejecting large volumes of small particles – sulphate aerosols – that enter the atmosphere blocking sunlight. Large volcanic eruptions can affect global temperature for decades. The researchers suggest that the spate of eruptions combined with a solar minimum, and ocean and sea-ice responses to the effects of the volcanoes, extended the grip of the freezing climate for over a century.

Within five years of the onset of the “Late Antique Little Ice Age”, as the researchers have dubbed it, the Justinian plague pandemic swept through the Mediterranean between 541 and 543 AD, striking Constantinople and killing millions of people in the following centuries. The authors suggest these events may have contributed to the decline of the eastern Roman Empire.

The findings are partly derive from a new temperature reconstruction, based on tree-ring measurements from the Altai Mountains, where Russia, China, Mongolia and Kazakhstan meet, that correspond remarkably well with temperatures in the Alps in the past two millennia. The width of tree rings is a reliable estimate of summer temperatures. Lead author, dendroclimatologist Ulf Büntgen from the Swiss Federal Research Institute WSL says, “This was the most dramatic cooling in the Northern Hemisphere in the past 2000 years.”

The multidisciplinary research team made up of dendrochronologists, climatologists, volcanologists, historians and linguists mapped the new climate information against a particularly turbulent period European and central Asian history. The volcanic eruptions probably affected food supplies – a major famine struck the region at precisely this time immediately followed by the pandemic.

A later “Little Ice Age”, between the14th and 19th centuries, has been well documented and linked to political upheavals and plague pandemics in Europe, but the new study is the first to provide a comprehensive climate analysis across both Central Asia and Europe during this earlier period.

“With so many variables, we must remain cautious about environmental cause and political effect, but it is striking how closely this climate change aligns with major upheavals across several regions,” adds Büntgen.

Several tribes migrated east towards China, possibly driven away by a lack of pastureland in central Asia. This led to hostilities between nomadic groups and the local ruling powers in the steppe regions of northern China. An alliance between these steppe populations and the Eastern Romans brought down the Sasanian Empire in Persia, the last empire in the region before the rise of the Arab Empire.

Northern Europe, including Scandinavia, also seems to have been severely affected by the volcanic cooling. “The extreme volcanic cooling of the mid-6th century coincides with the biggest desertion of farms and the largest reorganisation of settlement sites, as evident in the archaeological material, in Scandinavia and around the Baltic in the last few thousand years,” says Fredrik Charpentier Ljungqvist.

“The evidence for a severe decrease in population is rather clear. To what extent this was a direct consequence of famines following the drastic cooling is, however, not that clear. The devastating Justinian Plague, striking the Mediterranean in AD 541, may have reached Scandinavia and other parts of northern Europe,” continues Charpentier Ljungqvist.

The researchers conclude, “The Late Antique Little Ice Age fits in well with the main transformative events that occurred in Eurasia during that time.”

For more information, including the full list of authors, international contacts and figures, go to: http://www.pages-igbp.org/ini/wg/euro-med2k/nature-geoscience-2016-faqs

Cooling and societal change during the Late Antique Little Ice Age. Summer temperatures were reconstructed from tree rings in the Russian Altai and the European Alps. Horizontal bars, shadings and stars refer to major plague outbreaks, rising and falling empires, large-scale human migrations, and political turmoil.
Figure: Cooling and societal change during the Late Antique Little Ice Age. Summer temperatures were reconstructed from tree rings in the Russian Altai and the European Alps. Horizontal bars, shadings and stars refer to major plague outbreaks, rising and falling empires, large-scale human migrations, and political turmoil.

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