A recent study 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 Natural Resources Institute Finland suggests that the years 536 and 541-544 CE were very difficult for many people.
An extended period of little light may make 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. Read more.