The fall of Rome corresponds with the Late Antique Little Ice Age.
Climate change has been a permanent feature of human existence
I have borrowed heavily from an Aeon piece written in 2017 called ‘How climate change and disease helped the fall of Rome’ that the Smithsonian magazine (smithsonianmag.com) says has now been republished under Creative Commons. Attribution at the end of this comment.
In the middle of the second century, the Romans controlled a huge, geographically diverse part of the globe, from northern Britain to the edges of the Sahara, from the Atlantic to Mesopotamia. The generally prosperous population peaked at 75 million. Eventually, all free inhabitants of the empire came to enjoy the rights of Roman citizenship.
Five centuries later, the Roman empire was a small Byzantine rump-state controlled from Constantinople, its near-eastern provinces lost to Islamic invasions, its western lands covered by a patchwork of Germanic kingdoms.
Trade receded, cities shrank, and technological advance halted. Despite the cultural vitality and spiritual legacy of these centuries, this period was marked by a declining population, political fragmentation, and lower levels of material complexity.
However during this time politicians and rulers of Rome became more and more corrupt; Infighting and civil wars within the Empire were rife. [Echos of today perhaps]
…new evidence has started to unveil the crucial role played by changes in the natural environment. The paradoxes of social development, and the inherent unpredictability of nature, worked in concert to bring about Rome’s demise.
Climate change did not begin with the exhaust fumes of industrialisation, but has been a permanent feature of human existence. Orbital mechanics (small variations in the tilt, spin and eccentricity of the Earth’s orbit) and solar cycles alter the amount and distribution of energy received from the Sun. And volcanic eruptions spew reflective sulphates into the atmosphere, sometimes with long-reaching effects. …
But climate change per se is nothing new.
The end of this lucky climate regime did not immediately, or in any simple deterministic sense, spell the doom of Rome. Rather, a less favourable climate undermined its power just when the empire was imperilled by more dangerous enemies – Germans, Persians – from without.
Climate instability peaked in the sixth century, during the reign of Justinian. Work by dendro-chronologists and ice-core experts points to an enormous spasm of volcanic activity in the 530s and 540s CE, unlike anything else in the past few thousand years. This violent sequence of eruptions triggered what is now called the ‘Late Antique Little Ice Age’, when much colder temperatures endured for at least 150 years. This phase of climate deterioration had decisive effects in Rome’s unravelling. It was also intimately linked to a catastrophe of even greater moment: the outbreak of the first pandemic of bubonic plague.
See https://aeon.co/ideas/how-climate-change-and-disease-helped-the-fall-of-rome for the full story complete with nods to modern fiction of ‘climate change’.