It would seem that there are striking chronological parallels between significant variations of climate and major historical epochs, such as the Migration Period and the heyday of the Middle Ages. This is the conclusion reached following a study undertaken by researchers from Switzerland, Germany, Austria, and the USA, in which they were able to reconstruct the summer climate in Europe over the last 2,500 years from the information provided by annual tree rings.
. The decline of the Western Roman Empire coincided with a period after 250 AD in which it became much colder and climatically changeable. This phase of more marked climatic variation persisted for 300 years, accompanying the age of Migration and the associated socio-economic destabilization. The cultural revival of the early Middle Ages occurred as both temperatures and rainfall began to increase with the dawn of the 7th century. It is also possible that climatic factors may have contributed towards the spread and virulence of the Black Death after 1347. In addition, the new findings suggest that a cold period during the Thirty Years' War in the first half of the 17th century could have exacerbated the contemporary widespread famines.