More than a century before Vesuvius destroyed Pompeii and its neighboring towns, a colossal eruption on the other side of the planet apparently had much more far-reaching consequences for the history of ancient Rome.
The eruption of Alaska’s Mount Okmok in 43 B.C.E. triggered global cooling and other climate changes that may have compounded the famine, unrest and war that marked the last years of the Roman Republic, leading to its transformation into an empire, a new study in the journal Proceedings of the National Academy of Sciences suggested Monday.
By analyzing Arctic ice cores and ancient tree rings, scientists have been able to model the effects of the natural catastrophe on temperature and precipitation in the Mediterranean basin, the team of researchers explains.
This eruption by Okmok, the friskiest of the Aleutian volcano chain, occurred less than a year after the assassination of Julius Caesar in 44 B.C.E. Even before that famed murder, however, the Mediterranean region was engulfed in civil war. After Caesar’s demise a real-life Game of Thrones ensued between his political heirs and his assassins, from which Rome would emerge under the sole leadership of its first emperor, Caesar’s adopted son, Octavian Augustus.
To be clear, most historians agree that by the time Caesar was stabbed to death by Brutus and his co-conspirators, the ancient oligarchic institutions of the Republic were already in an irreversible decline from nearly a century of socio-economic strife and violent power struggles between ambitious generals and politicians. So, not unexpectedly, there is disagreement among scholars as to how much the Okmok eruption really contributed to the famine and misery that normally accompany war and instability, and whether the volcanic event was truly a major factor in the political transition of Rome into an autocratic empire.
“We’ll never know quantitively how much of an impact it had,” admits Joe McConnell, a professor of hydrology at the Desert Research Institute in Reno, Nevada, who is the lead author on the study. “We are certainly many decades into the crisis of the Republic and we are not saying that [the eruption] caused its downfall, but it undoubtedly had to be a contributing factor.”
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The force of 13,000 Hiroshima bombs
The perennial ice of the Arctic contains frozen bubbles of air and particles that can give us a pretty good picture of the chemical composition of the atmosphere in any particular year from today back to prehistory. By studying six Arctic ice cores, mostly from Greenland, McConnell’s team found that from early 43 B.C.E. to the spring of 41 B.C.E. the concentration of sulfur in the atmosphere was up to 30 times higher than normal.
This was the hallmark of a major volcanic event. Some eruptions inject plumes of sulfur dioxide into the stratosphere. The gas then becomes a veil of aerosol that can remain in the upper atmosphere for years, reflecting some of the sun’s rays and causing global temperatures to drop – the so-called “volcanic winter.”
In the same ice layers as the sulfur, the scientists found tiny particles of volcanic ash, and by studying their telltale chemical composition they were able to match them to known deposits from the so-called “Okmok II” eruption in Alaska.
This explosive event was largely responsible for the creation of a 10-kilometer-wide (6-mile-wide) caldera on Umnak island, in Alaska’s Aleutian archipelago. The eruption had not been precisely dated until now, but was known to experts as one of the two or three largest volcanic events in the last 2,500 years, McConnel tells Haaretz.
Okmok II was ten times larger than the Vesuvius eruption that destroyed Pompeii in 79 C.E., he notes. When the Alaskan volcano went off, it released an amount of energy equivalent to 200 megatons of TNT, or about 13,000 times the energy of the nuclear bomb that destroyed Hiroshima.
The eruption ushered in one of the coldest decades in the last two and half millennia. Ancient tree rings from Scandinavia, Austria and California show the northern hemisphere suffered rare summer frosts in the years 43-42 B.C.E., the scientists report in the PNAS paper.
The researchers also used computer simulations to model how the eruption would have affected the Mediterranean climate, finding that
temperatures may have dropped by more than seven degrees Celsius (12.6 degrees Fahrenheit) from seasonal averages, with the cooling effect persisting well into the 30s B.C.E. Precipitation levels may have also changed abruptly and violently: in some areas, rainfall increased to as much as 400 percent of normal levels.
Since Alaska is nearly 10,000 kilometers (6,000 miles) from Italy, ancient Rome's scribes would have been blissfully unaware that an entire island had blown up on the other side of the planet. But writers of the period do report of unseasonable cold, food shortages and famine across the Mediterranean, particularly in the years 43-42 B.C.E, the study notes. The historian Appian says that the city of Rome was “devastated by famine” and similar dearth was felt in Greece, where Octavian and his then ally, Marc Anthony, defeated the armies of Caesar’s killers at the battle of Philippi in 42 B.C.E.
Famine and pestilence wracked Egypt, the breadbasket of the Roman dominions, Appian also wrote; and the philosopher Seneca relates that in those two years the Nile did not flood, a key annual event in the region’s farming cycle.
War without end
It is fair to note that most of these historians wrote a century or two after the facts and of course, much of the disruptions in the food supply could be connected to the almost constant state of war in which the Roman Republic found itself.
Since the end of the second century B.C.E., even as it extended its control over most of the Mediterranean, the Republic was wracked by corruption, worsening inequality, social strife and political violence. As armies became more faithful to their generals than the state, powerful leaders began clashing with each other in full-blown civil wars: first Marius versus Sulla, then Caesar against his archenemy, Pompey the Great.
Caesar’s triumph over his rival was short-lived, and his assassination in 44 B.C.E. ignited a new round of conflicts that were fought across southern Europe and North Africa. Octavian and Anthony would vanquish the anti-Caesarians only to turn on each other in a final, bloody civil war. This culminated with the defeat of Anthony (and his lover, Egypt’s Queen Cleopatra) at the battle of Actium in 31 B.C.E. and the start of Octavian’s reign as emperor in 27 B.C.E.
With all this going on, do we really need to count a distant volcanic eruption and climate change as causes for the collapse of the republican political system?
No, argues Jonathan Price, a classicist and professor of ancient history at Tel Aviv University.
By 43 B.C.E., when the Okmok II eruption occurred, the Roman Republic’s political system was broken beyond repair, says Price, who was not involved in the study.
“If the eruption hadn’t happened, I don’t think it would have changed the outcome: we were already seeing the last gasp of the Republic,” he says. “If a patient has cancer that has spread to the whole body, and then he gets pneumonia and dies the next day, did the cancer kill him or the pneumonia? I think it’s the cancer.”
Besides, chronicles of failed crops, starvation and drought are common throughout antiquity, and certainly in periods of conflict like the civil wars that the Romans fought across the Mediterranean, he notes.
“Back then most people lived on the precipice of famine and hunger all the time, and there are records of harsh winters, failed crops and drought that look exactly the same in dozens or hundreds of other years in antiquity,” Price tells Haaretz.
Why did Egypt starve?
Other historians are less dismissive of the conclusions of the new study. The idea that a volcanic eruption may have contributed to the doom of the Republic is not entirely new. Kyle Harper, a professor of classics at the University of Oklahoma, has recently written about the theory based on data gleaned from Greenland ice cores in the 1980s. Back then the possible climate change was blamed either on a smaller-scale eruption of Mount Etna, in Sicily, which occurred in 44 B.C.E. or on a massive explosion at an unidentified tropical volcano.
Now that just such a volcanic event has been identified (granted, not in the tropics, but in the Arctic), the theory may gain more traction, supporting the possibility that, as McConnell puts it, “there were multiple factors causing these food shortages and disruptions at the end of the Republic’s life.”
“It’s not a climate event that changes the world, but one that exacerbates existing problems,” comments Edward Watts, professor of ancient history at the University of California, San Diego and author of the book "Mortal Republic: How Rome Fell into Tyranny."
“It could be one of those underlying conditions that don’t cause change but make a dramatic change possible, one that otherwise the system might have been able to resist,” says Watts, who was also not involved in the study.
While it is true that many of the accounts of famine, particularly those from Italy and Greece, can be explained as mainly the consequence of the civil war or direct military action, Watts does find it plausible to attribute the reports of dearth in Egypt to volcanic-driven climate change.
The fertile Nile valley, relatively untouched by the fighting, should have been able to increase production and help feed the Roman provinces, he says.
“This is a system that has a strong administrative capacity and can mobilize its resources quickly,” Watts tells Haaretz. “The fact that Egypt is not able to input more grain into the market does suggest something is going on and it is unable to respond to these stresses because of the climate shock. It makes sense.”