The study said: “Wet and warm summers occurred during periods of Roman and medieval prosperity. Increased climate variability from AD 250-600 coincided with the demise of the western Roman empire and the turmoil of the migration period.”

“Distinct drying in the 3rd century paralleled a period of serious crisis in the western Roman empire marked by barbarian invasion, political turmoil and economic dislocation in several provinces of Gaul,” it said.

Temperatures and rainfall only returned to levels of the Roman period in the early 800s, around the time when new kingdoms consolidated in Europe.