Apparently there's also records of the Romans growing grapes for wine in Britain.
> The Romans introduced winemaking to the UK, in a period with a relatively warm climate. Their vineyards were as far north as Northamptonshire and Lincolnshire, with others in Buckinghamshire and Cambridgeshire, and probably many other sites. The wines were most likely fruity and sweet, fermented with added honey, and drunk within six months.[15] Winemaking continued at least down to the time of the Normans, with over 40 vineyards in England mentioned in the Domesday Book; much of it was communion wine for the Eucharist.
> ... When Henry VIII was crowned in 1509, 139 vineyards were recorded, 11 of which produced wine for the royal household ...
> The twilight of British winemaking tradition was brought to an end with the onset of the First World War, as the need for crops and food, and the rationing of sugar, took priority over wine production. For the first time in 2000 years, English wines were no longer being produced in Britain. ...
> Viticulture was revived in the 1970s onwards ...
The Roman Warm Period (coming around Caesar era to 400s, explaining the Migration Age) The Medieval Warm Period And the inverse, the Modern Cooling Period (between 1600-1800, if I'm not mistaken).
All three explain macro population movements. Yes, the Germanic tribesmen were climate refugees. So were maybe the European colonists of the New World and other settler colonies.
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.
Remember that the 1700s was so cold relatively, the soldiers march even in summer with thick jackets and smokepipes.
Though, there was also the introduction of potato, which led to massive demographic explosion in the Protestant Northern Europe.
But I do see your point. Still, the Germanic tribes were the first climate refugees that we know, maybe after the 8.2 kya event [0] that led to the first cities in Fertile Crescent