We can coarsely divide the history of Western civilization into three periods: antiquity, the Middle Ages, and modernity. The boundary between antiquity and the Middle Ages is marked by the end of the Roman Empire and the beginning of the "dark ages." However, we can also mark it with a singular climate event: a "little ice age" in the 500s.

In 535, a volcanic eruption caused the entire planet to cool dramatically, creating famine and poverty around the world. A few years later, the first Black Plague Pandemic kill tens of millions of people. The plague would recur eight centuries later, also precipitated by a period of cooling and economic decline.

It looks like historians have taken up the link between climate and the dark ages in recent years, with papers (2)(3) and books on the subject.

We already attribute the rise of the Holocene Period to the end of the last big ice age. Now, with the explosion of climatology in the last few decades, historians have started to attribute major events like the fall of the Roman Empire and the Industrial Revolution to climate.