[jaratec]

> Yes, the Germanic tribesmen were climate refugees.

Not quite. Those germanic tribes were fleeing the huns. The crossing of the danube in 376 by the goths (as war refugees) and the crossing of the rhine in the winter 405/406 by the alans and vandals (as invaders) allowed them to escape the huns. There were extreme climate events recorded in the late antiquity, but that happened more than one century later. For example, https://en.wikipedia.org/wiki/Volcanic_winter_of_536 The Justinian plague occurred 541-549, amplifying the problems of the byzantine empire. Returning to the germans, also in the late antiquity, there is an obscure and unexplained event, in the period 500-550 the vistula and elbe basins were depopulated. Germans migrated from those places or they perished there.