Catastrophe: An Investigation into the Origins of the Modern World
David Keys found evidence for the climate change in dendrochronology--the study of patterns of tree rings to provide accurate historical dates. In 535/536 there was almost no tree growth, showing that the climate went haywire. A few documentary sources also point to a year or more of the sky being darkened and the sun paler than the moon.
The author's purpose in this book is threefold: to identify a possible source for this disaster, in a massive volcanic explosion between Java and Sumatra; to point to the likelihood of something similar happening again, with equivalent consequences; but most of all, to examine the impact of this climatic disaster on history.
This, the main part of the book, is the most fascinating, though also perhaps the weakest part of his argument. Keys traces the fall of the Roman Empire and consequent rise of Byzantium, the birth of Islam and many other major changes as powerful nations and civilisations crumbled or were overrun by invading cultures in Europe, Asia, the Far East and central and South America. Even the retreat of the British and the triumph of the Anglo-Saxons is tracked back to the fall-out from the volcano. Some of his arguments are very persuasive, though there are also many weak links, what ifs and maybes--but at least he is honest in expressing these.