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Unusual weather during Roman times plunged Eurasia into hunger and disease

A trunk of a subfossil tree was taken from a lake. Credit: Samuli Helama / Institute of Natural Resources of Finland

A recent study published in a prestigious academic journal indicates that volcanic eruptions in the mid-500s resulted in an unusually gloomy and cold period. A joint research project of the Chronology Laboratory of the Finnish Museum of Natural History and the Institute of Natural Resources of Finland (Luke) suggests that the years 536 and 541-544 CE were very difficult for many people.

A prolonged period of low light makes survival difficult. Food production, including agriculture and animal husbandry, depends on solar energy. Humans, meanwhile, become more prone to diseases if they are not exposed to enough sunlight to produce vitamin D.

"Our research shows that the climatic anomaly, which covered the entire northern hemisphere, was the result of several volcanic eruptions, "says Markku Oinonen, director of the Chronology Laboratory. The aerosols that were released into the atmosphere with the eruptions covered the sun for a long time.

Exceptionally poor weather conditions were significantly detrimental to agriculture and reduced the production of vitamin D among the population. This means that people who were already weakened by hunger also had to deal with compromised immune systems.

Trees are a record of the past

The study is based on dendrochronology or tree ring dating. The series of annual growth rings of subfossil or intact tree deposits covers the last 7,600 years. The trees are often found at the bottom of small lakes, and Luke has been taking samples and recording the findings since the 1990s.

"Researchers have developed an annual treeline pine growth rings calendar that covers more of 7,600 years, events can be contrasted with the calendar.The calendar of the growth ring is an important indicator of global climate change, "says researcher Samuli Helama of Luke.

The samples in the recent study were dated with the help of the growth ring calendar in Luke, and the researchers carved sample shavings of them for each calendar year. The Chronology Laboratory then performed isotope analysis on the samples.

The results of the study are based on the analysis of the variation of carbon isotopes in the annual growth rings of trees. The variety of carbon isotopes reflects the photosynthesis of trees, which in turn depends to a large extent on the amount of solar radiation available during the summer.

The new study traces the correlation of carbon isotope variation and volcanic eruptions from the nineteenth century to recent years, and shows the dramatic reduction of available sunlight in 536, as well as between 541 and 544 CE. The variation in summer temperatures was similarly reconstructed based on the density of annual tree growth rings.

The difficult times brought the plague

The unusually poor years coincide with the epidemic of bubonic plague that devastated the Roman Empire. The epidemic caused by the bacterium Yersinia pestis began in 542 CE and killed approximately half or more of the inhabitants of what was then considered the Eastern Roman Empire. The plague spread across Europe from the Mediterranean to possibly as far north as Finland, and had killed tens of millions of people in the 8th century.

Explore more:
Tree rings provide vital information to improve climate predictions

More information:
Samuli Helama et al, veils of volcanic dust from isotopes of tree rings of the sixth century linked to reduced irradiance, primary production and human health, Scientific Reports (2018). DOI: 10.1038 / s41598-018-19760-w

Journal reference:
Scientific reports

Provided by:
University of Helsinki

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