The book by Austen Atkinson, Impact Earth: Asteroids, Comets and Meteoroids: The Growing Threat hypothesizes an impact event. He reports that “the absence of an acid layer or ‘volcanic-fingerprint’ in ice cores suggests that there may have been another cause: atmospheric loading from space, an impact.” However, Cassiodorus, 534AD, reports such phenomena as “blue-coloured sun” which make me think of Benjamin Franklin’s reports from Europe of a “blue haze”.
The Laki Fissure event was very hard on Iceland and on Europe. The fluorine gases and ash destroyed the teeth of grazing animals, and 90% died off. About 10,000 Icelanders starved to death. Crop failures in Europe may have helped precipitate the French Revolution. Tambora in 1815 was also very bad, leading to “The year with no summer” in New England which helped promote migration from that area. Hope that we don’t have another such event in our lifetime.