Climate changes in the sixth and seventh centuries may have played a huge role in shaping human history, according to new research.

A paper published in the journal Nature Geoscience Monday identifies a period from 536 to about 660 AD as the “Late Antique Little Ice Age,” spanning most of the Northern Hemisphere.

The research highlights key climactic changes that began around 1500 years ago, significantly impacting history. “In particular, the sixth century coincides with rising and falling civilizations, pandemics, human migration and political turmoil,” it explained. The study’s authors cited, for example, the Justinian plague that ravaged the Byzantine Empire, the Sasanian Empire in the Middle East and the Mediterranean region in 541 and 542 AD.

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The researchers also identified movements out of the Asian Steppe and the Arabian peninsula, as well as the spread of Slavic-speaking peoples and political upheavals in China as the result of a cooler climate.

The study’s lead author Ulf Buntgen is head of the Dendroecology Group at the Swiss Federal Institute. Dendroecology is the scientific study of tree rings.

“Here we use tree-ring chronologies from the Russian Altai and European Alps to reconstruct summer temperatures over the past two millennia,” explained the scientists, in their paper. “We find an unprecedented, long-lasting and spatially synchronized cooling following a cluster of large volcanic eruptions in 536, 540 and 547 AD.”

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By spewing sulfur, volcanic eruptions can increase reflection of solar radiation back into space, cooling the Earth’s atmosphere. The cooling temperatures following the sixth-century eruptions were probably sustained by “ocean and sea-ice feedbacks,” according to the researchers.

Scientists are using climate to gain insight into key periods in history.

Last year, for example, a report published in the journal Science Advances challenged the long-held theory that Vikings settled on Greenland during warmer temperatures during the so-called Medieval Warm Period. Researchers analyzed chemical isotopes in boulders that were left by advancing glaciers over the last 1,000 years in Southwestern Greenland and nearby Baffin Island.