In general terms, the study indicates that periods of warm weather coincided with periods stability and growth. On the other hand, periods of cooler weather coincided with periods of turmoil and societal upheaval. The following is a rough Google translation of the Speigel article….
As it gradually became warmer [around] 300 BC, while relatively much rain fell, the Roman Empire flourished. The climate helped the Romans to the rise, as historians have noted, “The harvest yields, increased mining areas could be developed, Northern Europe, was recognized as soon as the road passable in the winter was over the Alps. Even in England the flourishing vineyards.
The data shows from the fourth century AD, a serious worsening of the climate [occurred]: it was cold and dry in central and southern Europe. Historians speak of the “Klimapessimum the Migration”. They know that provoked especially the invasion of the Huns, the migrations of the Teutons, Goths and other peoples. But it is clear that climate-induced crop failures, famine and disease exacerbated the [migration of] the Huns.
Europe experienced the greatest crisis of 536-546, when the summer temperatures plunged to a record low. “Our data show that time in an extraordinary ten-year depression,” says Ulf Büntgen. Frosty winds and darkness could ruin the harvest.
It was chilly times, as the new climate data [indicates]. The consequences were terrible: In the famine year 784, a third of the population of Europe died. “It was a rather cool summer,” is Büntgen sober diagnosis after looking at the new data. “With the worsening of the climate went back not only in Europe, the crops withered and cattle,” says historian Berninger. Each crop failure caused famine. For the cold came in the ninth century, then the humidity: Continuous rain offered fertile ground for epidemics. Leprosy was spreading.
My take on this research is that weather conditions have varied throughout history. The other observation is that I hope that global temperatures do not decline to levels seen after the fall of the Roman Empire or during the dark ages.