These images show a piece of ancient Irish oak wood, in which the ring-widths can be counted and measured for size. Bigger size equals better growing conditions, and this piece of wood happens to span one of the most famous episodes of extreme climate globally in the past two millennia, occurring from c.536-550 AD. There is an ongoing debate about whether the event was caused by a massive volcanic eruption and/or a comet loading the Earth’s atmosphere with particles that reflected incoming light and dramatically cooled the Earth’s surface. In the image, the year 532 is marked, in which the tree grew very well. But starting shortly afterwards (and especially from 536) you can see how the rings become narrower and narrower, and even become difficult to see. This reflects the environmental downturn that was in progress globally at this time, and which has been linked to famines and mortality in written sources from Ireland to China. One report in early medieval Irish chronicles for 538 notes a “failure of bread”. That this event was noted at all at this early period of Irish history, when written records are very scarce, suggests the seriousness of the conditions experienced at the time. This image also reveals the environmental background against which the great sixth-century plague of Justinian occurred.
We thank David Brown of Queen’s University Belfast for permission to photograph this oak sample.