Climate change contributed to the collapse of the Roman Empire. The Romans caused a lot of air pollution and deforestation, just like we do now. But in the long term, that had a lot less consequences.
Pope Gregory the Great (590-604) thought the end of the world was near. Life became hell in Rome, once the untouchable capital of the Roman Empire. The city was ravaged by floods. There was a famine. Plague epidemics broke out. Archaeological evidence is mounting that these and other catastrophic scenarios in the past were the result of climate change.
Roman air pollution
Deep in the Greenland ice sheets, in the 1990s, researchers found increased concentrations of lead and copper particles. They turned out to be the product of large-scale mining that took place in Spain and other Mediterranean areas around the turn of the Common Era. The large amount of particulate matter that was released had risen to the top and was then transported to Greenland via the stratosphere. Here it fell from the sky again as precipitation, was covered by snow and ice and was preserved that way until researchers brought it to the Earth's surface two thousand years later in their drill cores.
Large-scale Roman mining also increased emissions of the greenhouse gas methane exponentially (and is still measurable) from the first century onwards. The degree of air pollution at the height of the Roman Empire that can thus be determined was only surpassed again during and after the Industrial Revolution of the eighteenth and nineteenth centuries. Add to this the large-scale deforestation and it is clear that there was no modern environmental awareness yet.
Relationship between climate and behavior
No Roman could have ever imagined that man would leave a lasting negative mark on his environment, as is now the case with climate change brought about by human activity. Ultimately, the Roman economy was also not polluting enough to have adverse effects in the longer term.
This does not alter the fact that climate has become an important factor for antiquarians dealing with the Roman Empire. It was already known that society was completely dependent on a well-functioning agriculture at that time. However, new research makes it clear that the Roman Empire offers an interesting test case for establishing a possible relationship between climate, human behavior and the course of history.
To make things even more challenging, the Roman Empire appears to have encompassed several climatic zones including a multitude of microclimates. For example, we now know that when a humid period started in Roman Jordan, it became dry in Roman Anatolia (present-day Turkey), and vice versa. This kind of variation makes the reconstruction of the Roman climatic past more exciting but also more complicated at the same time.
Moreover, for historical climate research disparate different data must be combined in order to arrive at a coherent picture. From data on glaciers in the Alps, tree rings, stalagmites, clay layers, sediments in the Dead Sea area to solar activity and a study of the larger weather systems in the Atlantic and Indian Ocean area… all this kind of information needs to be gathered. included, discounted and set against each other. A heathen job.
Late Antique Little Ice Age
The first historically useful climate research from classical antiquity was therefore delayed until 2012. Since then, several new studies have been published and the study of the Roman climate is beginning to grow into a dynamic field of science.
What is the current state of affairs? In summary, three major climatic periods can be distinguished. Between 200 BC and 150 AD there was the so-called Roman climate optimum, a relatively warm and humid period in which the climate was stable. Between 150 and 450 this stability came to an end. It was on average slightly colder and drier. Finally, during the transition from late antiquity to the early Middle Ages, from 450 to 700, the negative trend continued and we speak of the Late Antique Little Ice Age.
Several factors play a role in the development of this relatively cold period. The most identifiable is the eruption of a volcano (it is unknown which one) around 530. The eruption sent so much volcanic material into the sky that contemporaries referred to it as "the year when the sun did not shine".
The period 536-545 is known as one of the coldest periods of the late antique Little Ice Age. Olive trees, grain fields, vines and orchards yielded a poor harvest, and the food supply for the entire population suffered greatly. The late antique Little Ice Age had disastrous consequences for that reason alone.
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These new insights, fascinating enough in themselves, only become meaningful if they can be placed in a larger historical and social context. The most interesting thing about the above periods is that they seem to coincide more or less with the great political developments and changes in Roman history with which we have been acquainted for so long from the well-known ancient written sources and the inscriptions.
Check it out. The climate optimum coincides with the greatest expansion and flourishing of the Roman Empire in the later republic up to the high imperial period. The climate started to deteriorate about 150 and from that time there are signs of political crisis and weakening. The first records of the Antonine plague date from this time. This smallpox epidemic started around 165 and continued to rear its ugly head for decades.
In the third century it was serious bumblebee in the Roman Empire. It struggled with incursions from outside the national borders and with money inflation. The emperors no longer came naturally from the ranks of senators in Rome but from the army. These soldier emperors often took each other's lives. Few of them died of natural causes. Political disintegration characterized this period, the empire fell into sub-realms. It now appears that the ailing climate further exacerbated the already difficult relations during this period.
Their first climate refugees
In the fourth century there was a political recovery and the climate recovered, albeit only in certain regions. In other regions, the negative trend continued and it became drier than before, making it impossible, for example, to grow grain or exploit olive trees. These changes, in turn, resulted in a net decrease in the total available agricultural area throughout the Roman Empire.
The Nile also flooded less regularly. Egypt was the breadbasket of the Roman Empire and so the consequences were felt in Rome as far away as possible. Not only in the Nile Valley, but elsewhere too, farmers who could no longer survive left their lands. This created a downward spiral that also made the impressive urbanization so characteristic of Roman times untenable. In North Africa, another granary, it rained less and the desert spread. No wonder we know late antiquity as a period of general decline and of political and socio-economic disintegration.
At the same time, it also became noticeably drier on the Eurasian steppes. Life for the Huns living here became difficult, if not unbearable. They moved to Western Europe, driving other groups such as the Goths ahead of them. We know their reputation from the history books. With their unruly horses, their asymmetrical bows and their swift cavalry, however, the initially unbeatable Huns in this scenario were not just an uncontrolled band of robbers who occasionally invaded the Roman Empire and terrorized from the border region. We can also see these Huns as the first documented climate refugees in the history of Europe.
2.5 degree already disastrous
To what extent is there a causal relationship in the correlation we observe between climate on the one hand and historical events on the other? For the time being, this question has proved difficult to answer, especially because most historians are reluctant to make connections that are too direct and too simplistic. The new insights, estimates and hypotheses raise many further questions. Not only about the reliability and interpretation of the data itself, but also about the relationship between people and the environment.
Nevertheless, all this new knowledge about the climate in the past does provide an exciting new dimension or variable that we certainly cannot ignore from now on. From our current perspective, it is especially instructive to see that a complete collapse of the system only required a small amount of climate change. According to data from the Roman world, a society could be completely unsettled at a difference of 2.5 degrees.
Pope Gregory the Great wrote about the late fifth century in his Bible Commentaries and Dialogues about its disastrous consequences. Rome, which once had a population of about a million, now had only 10,000 to 20,000. So let's be careful with our climate and let's do everything we can to prevent things from getting out of hand.