Science on the Edge

Who would have thought you could learn so much from tree rings...well, dendrochronologists I suppose, but who else? A very cool new study just recently published in Science has linked changing climate to the fall of the Roman Empire and a number of other historical events. The group, led by paleoclimatologist Ulf Büntgen, used 7284 oak samples from France and Germany, and 1500 stone pine and larch samples from high altitude regions of Austria to generate two sets of climate data for comparison.

In order to do this, they compared climate and weather records from the past 200 years with living tree ring data. This allowed them to observe how various temperature and moisture regimes affected tree ring growth. They then compared this data with timbers from historical buildings, preserved pieces of wood from bogs and rivers, and wood from archaeological sites to push back their timeline even further. When all of this data was combined they had a continuous records of the weather in France and Germany spanning more than 2500 years.

What they found was very interesting. They saw patterns which related times of social stability prosperity, like the rise of the Roman Empire between 300 B.C.E. and 200 C.E., with warm and wet summers ideal for agriculture. Similarly, these same climate patterns seem to be present in tree ring data corresponding with the height of medieval success in the region. And it was not just times of prosperity and success that were related to significant tree ring patterning. Times of turmoil and catastrophe were also readily observable in the data sets. For example, the period of widespread famine and plague starting around 1300 C.E. that wiped out half of the people in Europe within half a century was correlated with an extremely cold winter followed by consecutive wet and warm summers. Similarly, the period right before the Barbarian invasions and the eventual fall of the Western Roman Empire was characterized by extensive drought and poor agricultural conditions.

In addition to their climatological findings, they also noted some significant social findings in which wood cutting could be related to swings in social and economic activity for the region.

**The image used is an illustration of the Black Death as depicted in the Toggenburg Bible (1441)**