Climate change in antiquity and its economic consequences

Although political and social unrest during the 1^st century BC transpires from our recorded history, the underlying cause was not known. People understandably blamed the gods, the priests, and/or their leaders. In our 21^st century, we are able to pinpoint the true culprit, a rather unknown volcano in Alaska, the Okmok. 

Analyzes of the volcanic records in six separate cores taken from the Greenland ice cap have revealed two major volcanic eruptions that occurred approximately 8,300 and 2,050 years ago.  In-depth research enabled scientists to establish a more precise date in early 43 BC. As a result, the years 43 and 42 BC were among the coldest recorded in the last 2,500 years and started one of the coldest decades. The eruption led to colder seasonal temperatures in the Mediterranean region for at least two years.

[Timeline showing European summer temperatures and volcanic sulfur and ash levels in relation to the Okmok II Eruption and significant historic events of the Roman Republic and Ptolemaic Kingdom from 59 to 20 BCE [Credit: DRI]. From The Archaeology News Network]

Time-wise, this natural catastrophe coincided with significant historical events. Only one year before, Julius Caesar had been assassinated leaving the Roman Republic in utter turmoil. The state affairs somehow stabilized when Octavian proclaimed himself emperor of Rome in 27 BC. In the meantime, Cleopatra had been struggling to restore power in the Eastern Mediterranean. By 31 BC, she had to surrender to Octavian who took the title of Augustus Caesar as he founded the Roman Empire.

The problems Cleopatra had been facing were not only of political order. Egypt was suffering because the Nile failed to flood in 43 and 42 BC. Today we know that the eruption of the Okmok affected the Nile watershed. The scarce rain in some areas was not enough to replace the annual Nile River flood, causing food scarcity, famine, and disease. These facts have been confirmed by archaeological and written sources, but until now they were not linked to a volcanic eruption in the faraway Aleutian Islands. Further research has established that for at least two years, temperatures in certain Mediterranean regions fell nearly 7 degrees Centigrade below the normal average.

A local Egyptian governor left us an inscription dated about 39 BC, in which he describes his struggle to find food for the population as there had been no flooding of the Nile for several years. In this text, even the priests recognized this man to be a true savior of the people. Coming from them, clearly underscores the seriousness of the situation.

In the end, had Cleopatra and the Roman rulers known about the explosive eruption of that Alaskan volcano, there is nothing they could have done to avoid the famine and the chaos in their countries. With hindsight, however, we may – I think – be a little milder in judging their leadership. 

As recent as July 2008, the Okmok erupted again for five consecutive days reshaping the volcanic cone dramatically. Altogether, it remained active for a full month. However, I have not come across records of regional or widespread influences on the climate.