A joint research project of the Chronology Laboratory of the Finnish Museum of Natural History and Natural Resources Institute Finland (Luke) suggests that large volcanic eruptions in the years 536 and 541–544 CE resulted in unusually gloomy and cold period with little light, making it difficult for humans to survive. The level of production of plants is dependent on the amount of available sunlight. Food production, i.e, farming and animal husbandry, rely on the same solar energy. Humans, meanwhile, become more prone to disease if they are not exposed to enough sunlight to produce vitamin D.

The large volcanic eruptions of AD 536 and 540 led to climate cooling and contributed to hardships of Late Antiquity societies throughout Eurasia and triggered a major environmental event in the historical Roman Empire, study authors say. "Our set of stable carbon isotope records from subfossil tree rings demonstrates a strong negative excursion in AD 536 and 541–544."

Their model based on sixth-century isotopes reconstructs a solar irradiance anomaly for AD 536 and 541–544 of nearly three standard deviations below the mean value based on modern data and authors explain it by a volcanic dust veil reducing solar radiation.

"We offer a hypothesis that persistently low irradiance contributed to remarkably simultaneous outbreaks of famine and Justinianic plague in the eastern Roman Empire with adverse effects on crop production and photosynthesis of the vitamin D in human skin and thus, collectively, human health. Our results provide a hitherto unstudied proxy for exploring the mechanisms of ‘volcanic summers’ to demonstrate the post-eruption deficiencies in sunlight and to explain the human consequences during such calamity years."