The Exploring Environmental History Podcast has just published a very timely and fascinating issue about the effect volcanic eruptions may have had on European and World History. While Europe has not felt such effects in many many years, with the recent eruptions of Eyjafjallajökull on Iceland, starting with the disruption of air traffic, this has changed. Apart from traffic, the ash plumes are likely to affect crops, sun light, the climate and thus, economic, social and political history.
Host Jan Oosthoek digs into a couple of established events in the Middle Ages that show a combination of bad crops, decreased sun light and lowering of temperatures. He cites research that suggests volcanic eruption and ash plumes as an explanation for these. By extension, this connects famines, migrations, plagues and social instability to volcanic eruptions. It could mean that the Plague and the Renaissance may indirectly have been caused by volcanism. Oosthoek mentions no known volcanic eruption that could be a candidate for this explanation.
In turn, he goes over the recorded effects of the Laki eruption of 1783 (also in Iceland). Here he has no major occurrences such as famine, epidemic and revolution to report, yet the effect on weather and harvest in 1783 and 1784 seems considerable. In short, without being able to give definitive indications, with the eruption of Eyjafjallajökull we see environmental history in action.