Et tu, Etna?
In 44 BCE, a momentous event occurred. Somewhere on Earth, a volcano erupted—one of the largest of last 2,500 years terms of climate impact. Traces of the eruption can be found in ice cores from Greenland and Antarctica, in signs of cold weather in the growth rings of trees around the world, and records of famine and agricultural disaster from Egypt to China. The eruption caused global climate effects lasting several years.
Also, in Rome, a conspiracy of senators murdered Julius Caesar and the republic tumbled into civil war.
A group of young researchers say these events may be more closely intertwined than previously appreciated by classical historians focused on the internecine political machinations of the time period. They make the bold claim that the mysterious eruption in question is consistent with what seemed to be an unremarkable event at Mt Etna, a famous volcano in the center of the Roman provinces, in February of 44 BCE.
- Rafael Castro, undergraduate student in atmospheric science, University of California at Berkeley, Berkeley, California
- Isabel Fendley, geochemist, University of California at Berkeley, Berkeley, California
- Morgan King, classicist, College of St. Benedict and St. John’s University, Collegeville, Minnesota
- Tushar Mittal, planetary scientist, University of California at Berkeley, Berkeley, California
- Noah Randolph-Flagg, geologist, NASA Ames Research Center, Mountain View, California
This episode was produced by Liza Lester and mixed by Kayla Surrey.
Shane Hanlon: Hello Nanci.
Nanci Bompey: Hi. Happy birthday!
Shane Hanlon: Yes. It is my birthday on the day we’re recording this. Thank you, I guess. That’s surprising to say. Before we started recording we were talking about birthdays. The episode is kind of about bad omens. We were wondering if anything bad has happened on our birthdays. Not to us or on the exact date, but what’s our day… Number, I guess.
Nanci Bompey: It just so happens that on my birthday a couple of interesting things happened, and one of them I do recall. Before I was born, it was the date of the Watergate break-ins.
Shane Hanlon: So you’re not that old.
Nanci Bompey: Not quite that old. What I do remember when I turned 16… it was the day that there was the chase with OJ Simpson and then he got arrested with the white Bronco. We were having a party at my friend’s house in high school and watching that on television.
Shane Hanlon: Like a birthday party?
Nanci Bompey: Yeah. Everyone was watching that.
Shane Hanlon: So you were at a birthday party for yourself watching the… wow. That’s… Do you think that’s personally affected you? Were you like, “This ruined my…”
Nanci Bompey: No, I don’t think so. I just remember that that happened on my birthday, which is interesting.
Shane Hanlon: I think that counts.
Shane Hanlon: Welcome to the American Geophysical Union’s podcast about the scientists and the methods behind the science. These are the stories you won’t read in the manuscript or hear in a lecture. I’m Shane Hanlon.
Nanci Bompey: I’m Nanci Bompey.
Shane Hanlon: This is Third Pod from the Sun.
Shane Hanlon: Of all the things that I would’ve imagined that would’ve happened on a date, that wouldn’t have been it. I can’t believe that happened on your birthday.
Nanci Bompey: I know, it’s crazy. It’s interesting.
Shane Hanlon: Well, we’re not here to talk about your birthday, my birthday, anything like that. But I did mention that we’re hear to talk about bad omens. To explain this episode, our producer for this one… We’re going to bring in Liza Lester.
Liza Lester: Hey Shane.
Shane Hanlon: Hi Liza. I guess I could’ve said hello. I don’t know why I awkwardly paused there.
Shane Hanlon: Anyways, what are we here to talk about today?
Liza Lester: We’re going to talk about volcanoes.
Shane Hanlon: I like volcanoes.
Liza Lester: Also the Ides of March.
Nanci Bompey: Isn’t that something Shakespeare?
Liza Lester: That’s right. It’s Shakespeare.
Shane Hanlon: Wait, how is… It doesn’t matter. Keep going. This will be forever if we keep doing this. This will be a side episode.
Liza Lester: So we’re talking about omens and momentous events. 2,000 years ago, in 44 BCE, there was a volcano that erupted somewhere in Earth and we know this because of ice core records. Do you remember ice cores?
Shane Hanlon: Mm-hmm (affirmative). We’ve done stuff on ice cores.
Liza Lester: We’ve done stuff on ice cores. The ice cores recorded large amounts of sulfur and particulates from somewhere in the world. There was a volcano, but we don’t know where, but we know it was big and somewhere near the equator. Also in 44 BCE, Caesar was assassinated. Remember that?
Shane Hanlon: The Ides of March.
Liza Lester: Ides of March, exactly.
Shane Hanlon: I’ve got it.
Nanci Bompey: Oh, it’s Shakespeare because it’s a play, right?
Liza Lester: Right, Julius Caesar.
Shane Hanlon: I like that we keep coming back to Shakespeare. Thank you.
Liza Lester: None of us can quote it.
Shane Hanlon: No.
Liza Lester: Also in 44 BCE, Mount Etna… which is on Sicily, down at the boot in Italy, so right in the middle of the Roman Republic at the time which extended all the way around the Mediterranean… also erupted. But volcanologists hadn’t thought these things were related because that eruption didn’t seem to be that big.
Shane Hanlon: I think I see where this is going.
Liza Lester: But it was big enough that it was effects in Rome. These effects happened to be rolling in around the time that Julius Caesar was assassinated. Kind of bad omens, right?
Shane Hanlon: There we go. We’re bringing it all back together.
Liza Lester: Writers at the time recorded these effects. Here’s classicist Morgan King reading a description from an eyewitness… that is Virgil, the rockstar poetic of the Roman era in the Augustan Period.
Shane Hanlon: Rockstar poet.
Liza Lester: He was! In the Augustan Period, which was… Augustus was the first emperor of Rome. He was Julius Caesar’s heir and adopted son. He took over in that turmoil after his death. Virgil wrote this really big poem about farming and weather and this is from that poem.
Liza Lester: We’re talking about poetry.
Morgan King: Okay, I can read you the Virgil lines. [Latin 00:04:55]. These are a couple of lines from Virgil’s Georgics, the farming poem. “When Caesar had died, even the sun pitied Rome when it covered its head with dark shadow, and the impious generations feared eternal night.”
Liza Lester: That’s dramatic.
Morgan King: Yeah. It’s a mood. I think it does get this idea… The line really strikes me in light our project that “the impious generations feared eternal night…” I think that captures something of this experience of suddenly you can’t see the sun.
Liza Lester: Will it come back?
Morgan King: How do you know? We think it actually took a year or two for things to go back.
Liza Lester: That’s a long time.
Morgan King: It’s a long time and you don’t know why it happened and there’s no way to know when it’ll be over. I think it’s a really dramatic experience.
Shane Hanlon: I guess this makes sense if your leader was just killed and the sky has turned black. You can see why that’d be a bit ominous, or I could at least.
Liza Lester: Especially if you’re tending to see portent in astrological events and things happening in nature. The idea was… among classicists and historians… that poets at that time were describing that mood in Rome and attributing to the natural world the feelings of the people and reflecting that mood metaphorically, which does make sense because they did see omens and portent and symbolism in what was going on in the natural world. But Morgan is saying that maybe they’re also literally describing what was going on and that maybe some of this environmental disaster that occurred could’ve been overshadowed by all of these political things that were going on, which were pretty dramatic and complicated.
Shane Hanlon: Considering our current climate… not commentary on that… you can think about that there’s other stuff going on in their world but there are certain things that are at the forefront of everything and so what people are paying attention to.
Liza Lester: There’s a lot of writing about that and all of the complicated backstabbing events going on in all directions. After these darkened skies came several years of cold. We know this from tree rings. Remember tree rings?
Shane Hanlon: Yeah. This is like our review episode.
Liza Lester: So frost damage in trees that are long lived show that it was cold and there are financial records of trades being impacted and famine and maybe they thought the famine was from warfare, but Morgan and some other researcher are about to look back on other records not just in Rome but extending as far as China and southeast Asia where there was famine, crop failures. They noted that people were burying all their gold because that’s what you do when things are bad. There’s evidence that these problems weren’t just in Rome but were extending perhaps around the world.
Shane Hanlon: Wow. That’s intense.
Liza Lester: Yeah. Then the question is could this eruption at Mount Etna have been responsible for all this climactic… climatic? Climate events that were happening.
Shane Hanlon: That’s fine.
Liza Lester: When Morgan was at Berkeley finishing her degree, she worked with a bunch of scientists and they tried to model whether this volcano in Sicily could have impacted the global climate in this way.
Shane Hanlon: I’m excited for this.
Liza Lester: You want to go? Let’s start by setting the political stage. We’ll bring in our classicist first.
Morgan King: Hi. My name is Morgan King. I’m a visiting assistant professor of classics at the College of Saint Benedict and Saint John’s University in Minnesota. I work on Roman cultural and literature, especially of the Augustan Era.
Liza Lester: This was a big period of transition for the Roman Empire. What was going on at the end of the Roman Republic?
Morgan King: A lot. It’s a really complex time period and to fully understand it you have to go back considerably further. A lot of historians will go back to about the 120s BCE for the start of a cycle of political violence. Romans themselves will go back even further to winning the Punic Wars against the Carthaginians because nothing is as damaging to Roman psyche as victory.
Liza Lester: Was that Hannibal coming over the Alps with elephants?
Morgan King: Exactly. Some Roman historians think that being too successful is what makes things go wrong. Modern historians will state the beginning of the fall more to the start of actual civil violence in the Republic… serious civil violence which starts about the 120s. There are a lot of political-military factors that go into the time period, but to give a broad view of it you get power increasingly consolidated under individual successful generals and politicians who then end up fighting each other for more control over Rome and it’s provinces. You get an escalating series of political violence in the city and also civil wars.
Liza Lester: The Roman Empire had a representational government like we do now?
Morgan King: No. It’s interesting and complicated. They had a republic, which did have voting rights for citizens, however the voting rights were stacked towards the wealthy. It’s still oligarchical in a lot of ways. Oftentimes in pop culture we think of the fall of the Republic as the fall of this democratized form of government and it definitely wasn’t that. It was a cabal of elite people who wanted to maintain that collective elite control. I wouldn’t romanticize the fall of the Republic in quite the ways that popular culture does but on the other hand you had a wider collection of people who had access to power, whereas in the Empire it’s going to be really centered in the imperial family and it’s going to based around a single household.
Liza Lester: Was Julius Caesar a popular figure? Would the average Roman be like, “I support Caesar because this is someone who is exciting who I know who is out conquering things for Rome”?
Morgan King: Yeah. He was a popular figure and he was associated with a party called the [Populares 00:12:44], and some of his political strategies were things like giving away money to the people, which is a thing that will make you popular with lower classes. He was also very generous to his soldiers and successful as a general. He was able to give his soldiers a lot of money, which made them loyal to him which was a very effective political strategy. He did have a lot of popular support and we see things like in his will he makes a giant donation to the people of Rome. That also rouses a lot of popular anger about his murder and you see riots at his funeral.
Liza Lester: Events leading up to his death in 44 BCE… What’s going on in Rome in those last years?
Morgan King: A couple of years previously things had come to a head between him and his biggest rival at the time: a guy named Pompey, who was his son-in-law for a while despite being considerably older than Caesar. Pompey was married to Julius Caesar’s daughter Julia, his only living child, but she dies in childbirth and shortly thereafter things disintegrate between the two of them. Pompey and a collection of senators who are very suspicious of Caesar try to maneuver to decrease Caesar’s power. Caesar has been on campaign in Gaul and he’s supposed to come back.
Morgan King: Traditionally, as a Roman politician, you have to leave your army in the province where it belongs and then you come back to Rome and if you want to you can run for office and if you get into office you get power, but also you get immunity from prosecution. No one can prosecute you for anything while you’re in office. This whole question has become very on point for contemporary politics. In Rome it’s a very set thing: that you can’t be prosecuted while in office. But according to normal rules, in order to run for office you have to physically be in Rome. He has to leave his armies to do that.
Liza Lester: In Gaul, which France now.
Morgan King: Right.
Liza Lester: You can’t bring your army with you into Rome to then run for office with them at your back.
Morgan King: Caesar doesn’t like this situation where he knows that his enemies are going to prosecute him if there’s a portion of time where he’s not immune and doesn’t have the power of an army with him. This is where we get that moment… it’s come into popular parlance… the crossing of the Rubicon. This is the moment when Julius Caesar decides that he’s going to take his army with him into Italy: that he’s not going to play this game and that he doesn’t want to be vulnerable to his political enemies in that way. This starts a civil war with Pompey and the senators who are with Pompey, which they lose.
Morgan King: So Caesar wins. It takes a couple of years, but he manages to break the power of the opposition. But he’s also into this idea of mercy. He doesn’t want to be a king. He doesn’t want to totally break the system in Rome. He just wants to have power and safety, or at least that’s how he would present it. He doesn’t actually kill his enemies. He pardons all of them. He makes this big show of forgiving them and welcoming them back into the fold if they’re willing to play by his rules. He does that and things are moving towards a new normal in which he holds all of the power but ostensibly republican systems are still in place. He tries to work out a new system on top of the old system, and one of the ways he does this is that he ends up taking this traditional role of dictator, which is in the Roman history a legal, normal political role.
Liza Lester: It doesn’t have the vibe we give it now.
Morgan King: It gets that in large part because of what happens with Caesar. But traditionally, actually very limited and it’s to respond to a specific crisis where they’re like, “The consul thing is too dispersed. Not enough power. We want a more centralized executive to deal with this crisis.” The model of Cincinnatus is he comes, he wins the war, and then he goes back to his farm, and that actually happened in the Punic Wars against Carthage and at other times. Rome had dictators and they did the thing and then they went home. But Julius Caesar decides that maybe this is the closest thing to what I want to be, is dictator but forever.
Morgan King: He decides he’ll be dictator for life and he’s trying to pull together a new system on top of the old. But he did let all of these people who didn’t like him and didn’t agree with this vision live. They start plotting to end this: to make things go back to the way they were, or at least how they think that they were or should be. That’s how he ends up getting assassinated by a group of these people, many of whom had fought against him in the previous civil war, which is also part of the reason why his grandnephew does make the same mistake but instead kills all of his enemies.
Liza Lester: No mercy.
Morgan King: No mercy. That game ends with Julius Caesar.
Morgan King: On the one hand, in 44… before Caesar’s assassination… things look somewhat stable for a short amount of time, but also moving towards something new.
Liza Lester: How long was Caesar serving as dictator before he’s killed?
Morgan King: This dictator for life position was very soon before he gets assassinated. I believe it’s in January of 44 and he’s assassinated in March.
Liza Lester: Months.
Morgan King: Yeah, a couple of months. That role ends up for life but a very short…
Liza Lester: Life was not long. March 15: the Ides of March. What happens after he’s killed? There’s riots at his funereal and trouble across the Empire, which at this point extends how far?
Morgan King: Spain all the way up to Gaul… so modern day France… all the way east into modern day Israel. Egypt is not technically a province yet but it’s tightly intertwined. North Africa is a province. You’ve got a big circle around the Mediterranean. It’s not the largest extant that it will be, but it’s a lot of what you think of when you see the maps of the Roman Empire.
Liza Lester: But then Caesar is murdered and there’s trouble.
Morgan King: It creates a huge power vacuum. It turns out that the assassins hadn’t fully thought this through. They kind of thought that if they killed Caesar it would go back to the way it was: that Caesar was the problem. But Caesar wasn’t the problem. Caesar was part of the problem, but the problem was bigger and more systemic. When Caesar dies, there’s a power vacuum and people start competing to take up that power and control that Caesar had held. And there are also all of these angry mobs and legions who are very loyal to Caesar who are unhappy about how things are.
Morgan King: On the one hand, you’ve got the assassins and the senatorial elite who want to reclaim more of their power, but then you’ve got people competing to take over Caesar’s spot. There are two people who do that: Caesar’s great-nephew, who he names as his heir… a guy named Octavian, later to be dubbed Augustus… and also Caesar’s right-hand man in the military… a guy named Antony. It’s an interesting generational thing because Antony is in his prime of life. He’s a veteran of all of these campaigns with Caesar. Really well established. Known and trusted by the legions. Octavian slash Augustus is like 17 years old. He’s a kid. He’s basically at college. He gets the word that his great-uncle… who also adopts him as his son in his will… After that, Augustus Octavian makes a big deal of being the son of Caesar, which is totally normal for Romans: to just adopt people in your will. It feels weird today but that’s how things worked.
Morgan King: He gets the call that his great-uncle/father is dead. What are you going to do? He rides into town and says, “I’m going to swing for the fences on this. I’m going to be the next Caesar.” Antony is not so happy about that. Antony thinks he’s going to be the one to take up that mantle because he was right next to Caesar the whole time. So you’ve got power battles going both within the Caesarian party and between them and the senatorial classes. For the next two to three years, you see a number of small scale skirmishing and then all out civil war break out between those three interconnected factions. Eventually, Octavian and Antony team up and fight it out with the senators. The famous one in popular culture is Brutus. At the battle of Philippi, they defeat Brutus and the other senators and break that power and come up with their own treaty: what they called a triumvirate, where they share power in the Empire… the two of them… and then a third guy who’s there just to keep the peace. He gets knocked out early.
Morgan King: Eventually, Octavian and Antony are going to duke it out again. If you’re familiar with Shakespeare, Antony and Cleopatra, that whole saga shakes down in the 30s and eventually Octavian defeats Antony and Cleopatra and then he gets total control. It is a slow moving avalanche of… And these years are particularly fraught and confusing if you don’t study them because there’s a lot of double crossing and…
Liza Lester: They’re allies, they’re not allies.
Morgan King: One minute Octavian seems to be allied with the senators and that senatorial party and then he’s back with Antony and then he’s killing Antony. Well, Antony commits suicide, but causing the circumstances in which Antony will commit suicide. It’s a very Game of Thrones complex power vacuum kind of situation.
Shane Hanlon: So there’s a lot of stuff going on politically at the time. A lot of interesting things that we’ve learned about in some capacity.
Liza Lester: Shakespeare.
Shane Hanlon: Back to Shakespeare. That’s the politics side of it, but what about the volcano?
Nanci Bompey: Yeah. I was promised a volcano here, Liza.
Liza Lester: Right, the volcano. In February, this volcano erupts on Sicily.
Shane Hanlon: It’s February now.
Liza Lester: This is actually a pretty big mountain. It’s like 10,000, 11,000 feet. It’s one of the bigger mountains and it’s one of the most volcanically active mountains in Europe. It erupted last year in 2019.
Morgan King: The ash cloud hits Rome the day after Caesar’s assassination apparently. Caesar is assassinated and the skies turn dark. The sun is blotted out from the sky, apparently. From all accounts to Romans, it felt like an apocalyptic moment: that all of this crazy stuff was happening not just in politics but also in the world around them. This eruption and the skies turning dark… A bit later, there’s also a comet that’s seen, which then gets interpreted as Caesar ascending into the heavens as a god. They end up believing that he became a god after his death, which then Octavian Augustus also makes a big deal of. He spends the rest of his life not just calling himself the son of Caesar but the son of Caesar, the god.
Liza Lester: This is helping him be like, “I’m the scion of the god.”
Morgan King: “I’m literally the son of a god.” There’s a lot happening and a lot of historians writing at the time… Poets will list the crazy things that happened these years and how out of control and out of whack the natural world seemed in this moment. Our project is looking specifically at this eruption of Etna, which we think caused widespread effects and could’ve been responsible for a number of different effects that Romans didn’t associate with that eruption. There were also a bunch of solar effects, which you can get from having aerosols in the atmosphere that mess with how you see the sun. Famously, when Octavian comes to Rome… he’s coming back from college and into Rome to try to become the next Caesar… people see this ring around the sun: this halo. That gets interpreted as divine favor for Octavian: that this is a really… It seems like a good thing for the sun to have this giant halo as this young man who’s the heir of Caesar returns, as opposed to the darkened skies.
Morgan King: Romans are interpreting these environmental effects as really meaningful. They’re also saying that they go on for a long time. A lot of the sources say that the sun didn’t shine as brightly for about a year. I think it’s interesting to think about how that would shape your experience of this moment of political turmoil: to also go outside and not be able to see the world as you have remembered it.
Liza Lester: Even if you know, it’s still affecting the way you feel about what’s going on, I think: that feeling of gloom and almost like the sky is grieving. Did Romans at the time know it was a volcano that was creating this darkness in the skies? Was it raining ash on Rome?
Morgan King: That’s an interesting question. In my field, one of the famous descriptions of this comes from the poet Virgil, who is the Roman poet. He writes about this in this big poem he writes about farming. In the first book, it’s all about the natural world and weather and he talks about how the sun pitied Rome when Caesar died and he talks about how the skies turned dark, and then moves immediately from that to describing the eruption of Etna. He doesn’t explicitly say that it’s the cause, but the two seem linked in the progression of thought. It’s not totally clear if…
Liza Lester: That they knew the cause and effect, but they know that they’re happening at the same time.
Morgan King: And they’re definitely associated. I don’t think there’s any clear sense that they’re linking the solar effects to Etna, and we also think that famines around the Mediterranean probably were also caused by this. Romans didn’t have a clear sense that that was going to be linked to Etna either.
Morgan King: Another interesting aspect of the project that we’re working on is that the effects of such a gaseous volcanic eruption as so dispersed… they’re very dramatic, but a lot of them are happening far away from Sicily. It’s not just the rock and fire right there, it’s the climatic impact around the Mediterranean and around the world, even.
Liza Lester: Changes the temperatures and so your crops aren’t maturing the way they are expected and you have famine and presumably unrest goes along with famine because people are hungry.
Morgan King: It’s an interesting thing. I think of Romans were attributing famine to the political unrest, which has its own set of causes that we’ve talked about. I think part of what our project [inaudible 00:32:07] too: maybe there are multiple causes here. Political unrest may also be helping to cause famine and the famine may also be… there may not be that much crop to take in anyway because of the weather. You have multiple causation and one thing that we’re interested in is the way that the political unrest may have obscured how bad the environment unrest was.
Liza Lester: They attributed it to this political unrest because it’s so dramatic for the time, so historians and classicists look at this and they think, “Yeah, it was famine because there was war, there was uncertainty.”
Morgan King: Right, we’ve got a cause. I don’t want to discount that as a cause, but it’s possible too that there’s another layer of things happening here that we haven’t been able to see as clearly because it was such a tumultuous time period.
Liza Lester: When you look past Rome to other empires around the world, do you see evidence of this volcano?
Morgan King: Yeah. There is evidence also in China of massive famines during these years, which maps up pretty well with the aerosol mapping that the geologists in our team have done.
Liza Lester: We’re going to talk with them about it some more.
Morgan King: It really does geographically match up pretty well. I’m not an expert in ancient China, but we do have records of famines there. The impact was global.
Liza Lester: Is this the first time that people have thought about Mount Etna having these effects on the politics of Rome at this time and being a big volcano that had…
Morgan King: Actually no. There was an excellent paper from 1988 by a woman named Phyllis Forsyth. Noah and I had a fantastic conversation with her. She did this as a solo project. She talked about how challenging it was moving into a scientific angle of classics and that she had to really work to get people to take her seriously.
Liza Lester: And to read and understand a whole different field.
Morgan King: Yes. It’s an enormous amount of work, so I’m grateful to be working with geologists who specialize in volcanoes.
Nanci Bompey: Geologists? We know some geologists!
Liza Lester: We know a lot of geologists.
Shane Hanlon: So she talked to geologists, right?
Liza Lester: Yes. She worked with them. They did a bunch of modeling to match the historical data that she was contributing.
Shane Hanlon: Let’s hear from them.
Rafael Castro: I’m Rafael and I’m an undergrad at UC Berkeley studying atmospheric science.
Isabel Fendley: Hi. I’m Isabel. I’m a graduate student at UC Berkeley and I study volcanoes and climate, specifically the largest volcanic eruptions which often coincide with crazy climatic events and mass extinctions.
Tushar Mittal: Hi. I’m Tushar. I’m a graduate student at UC Berkeley also. I study how volcanoes and climate interact on a variety of timescales from a theoretical perspective. I’m trying to understand volcanoes underwater as well as on land.
Noah Randolph-F…: My name is Noah. I’m a post doc at NASA, but most of this work was done when I was UC Berkeley studying volcanoes and climate and hot springs. Our study was seeking to answer two questions: what was the climate and the lived experience that people in 44 BC was like and that experience is variable in space and time. We different resolution from proxy records of what life was like in China and what life was like in Chile and what life was like in Rome. It’s very different in those different places and that’s giving us some resolution into what be going on at that time. The next question is was Etna responsible for these changes? That’s a spacial question and it’s asking, “Would Etna be able to produce the effects we see in Rome and Greece and not produce anything in Tasmania?” There’s variations laterally across the world. There are also variations depending on the height of particles in the atmosphere. There are some effects that are related to particles that you’re actually inhaling while there are other effects that are due to particles in the upper part of the atmosphere that are reflecting sunlight.
Noah Randolph-F…: Our approach was to answer these questions in space and in time, and answer if Etna was responsible for this distribution of effects.
Liza Lester: I think one of the things that I thought was interesting about this was that there’s this mystery of this large volcano that we see in the ice core record. Tell me about the ice core record and how we know that there was this big volcano around 44 BCE.
Isabel Fendley: In ice cores, we see changes in the chemical composition when there are these large volcanic eruptions. These eruptions are large enough that some of their gasses… which ultimately turn into sulfate aerosols… are being deposited worldwide. We can see these sulfate aerosols recorded in the ice cores. When we see the sulfate both in the northern hemisphere… so in the Greenland ice core… and in the southern hemisphere… in an Antarctic ice core… we know this eruption is so large that it’s distributing material worldwide. That’s when we start to hypothesize that maybe it had an effect on the climate or an effect on ecosystems or people. These ice cores are generally considered to be so far from any other sources of sulfur that it has to be coming from the atmosphere, and when you think about what’s coming from the atmosphere volcanoes end up being one the only sources.
Noah Randolph-F…: In modern times, one of the largest sources of sulfur are cars, but thankfully in 44 BCE that’s not a problem.
Liza Lester: They didn’t have cars back in the late Roman Republic, so we’re not confused by the signal. That’s a good point.
Tushar Mittal: Also, to add on that, we have some examples where… for instance, for the 1991 Mount Pinatubo eruption, as well as other eruptions like Tambora 1815 and the Krakatoa eruption… we know that there was a big eruption and then when we look in the ice cores we see a consequent increase in the sulfate aerosols. That provides some confidence that this idea that you can go to the ice cores with very high resolution… we can resolve things almost on the early timescales. Seeing sulfur there corresponds to large volcanic eruptions happening worldwide.
Noah Randolph-F…: There’s actually a bit of a puzzle. The largest eruption in the 20th century was Novarupta, which was in Alaska and produced this giant eruption and pretty much no climate effects as far as we can tell. In 1991 there was an eruption that was smaller and produced dramatic climate effects, including… people estimate… almost a 10% in crop yields globally. One question that people have had is why do some volcanic eruptions produce effects and why do some others not? We think that answer is intimately related with sulfur.
Liza Lester: This invisible sulfur that’s coming out of the volcano could have these profound global effects on climate because what effect does it have in the atmosphere that it changes the way crops might grow or the temperatures we might be experiencing on the ground?
Tushar Mittal: The main effect with regards to sulfur from large volcanic eruptions is that large volcanic eruptions can put sulfur not just in the lower atmosphere but high above in the stratosphere tens of kilometers up. Because in the stratosphere you get all of the sulfur, there’s much less sulfur from sulfate aerosols which reflect our sunlight much more efficiently than before. As a result, you get a cooling effect, which is the traditional effect that people see for Mount Pinatubo and other large eruptions. You also get an effect… Because you’re reflecting more sunlight, it’s been hypothesized that as a result plants get lower radiation and that effects their crop yield.
Tushar Mittal: There’s a number of effects, and if the volcano does not put sulfur high up in the atmosphere… because of water vapor in the lower atmosphere, the lifetime of sulfur is much shorter: on the order of weeks. If you put it high enough, there’s not enough water vapor to convert it into sulfate aerosols rapidly and then the sulfur can persist for multiple years and produce global signals rather than local signals.
Isabel Fendley: Also, to clarify with respect to plants, when we say irradiation we mean light in this context, not anything else.
Liza Lester: Good clarification.
Liza Lester: So when you drill down into the ice in the Arctic or Antarctic, if you’ve had a large eruption you can see a signature at the time that this ice was put down… this snow… and it tells you something about how big that eruption was compared to the ones that we know about, because we’ve seen them and experienced them here today. You saw this signature that happened in 44 BCE or around then, which was right around the time that Caesar was murdered. It’s notable in our history. How big does that signature look compared to some of the eruptions we might be more familiar with like Krakatoa or Helens or Pinatubo?
Tushar Mittal: With regards to the sulfur signal that we see in the ice cores, the eruption in 44 BC is either the third or fourth largest in the last 2,500 years of ice cores records. It’s about one and half to three times larger than the 1850 Tambora eruption, which we also see with large scale global effects including the year without summer in Europe and a lot of other history aspects.
Isabel Fendley: Coincidentally, the year without a summer may be responsible for the writing of the Frankenstein novel.
Liza Lester: I’ve heard about that.
Isabel Fendley: Isn’t that amazing? Fun fact.
Tushar Mittal: It’s something like five to 10 times larger than the Mount Pinatubo eruption, which had been associated with some [inaudible 00:43:14] in global warming in the modern era. It’s a very large eruption and we don’t know where it is.
Noah Randolph-F…: The other big eruption that people like to put things in context is… Ben Franklin was hanging out in Paris in 1783 and there was a large eruption in Iceland. People have modeled that. It’s called the Laki eruption. People have linked that to the French Revolution and models where people say how many people would’ve died just due to the respiratory effects of breathing all of that terrible air. I think 150,000 people died within a few years of that eruption, so it was a really hard time. Crops failed. There was snow in the summer.
Liza Lester: But you wouldn’t have necessarily known at the time that the illness you were experiencing was from this volcano in Iceland.
Noah Randolph-F…: Exactly. In the peak that we see after… that we’re arguing is due to… Mount Etna is twice what was observed after that 1783 eruption. We’re talking about a large anomalous event.
Liza Lester: So, mysterious eruption somewhere in the world at this time. The ice core tells you when but not where because it’s a global signature.
Isabel Fendley: It can tell a little bit about where: not very specifically. But since there’s a larger anomaly in the northern hemisphere… in the Greenland ice core… we infer that it’s probably somewhere in the northern hemisphere, though you also see it in Antarctica.
Liza Lester: You can narrow it down to the northern hemisphere. Still a big area.
Tushar Mittal: And it has to be mid-latitude or close to the equator so that most of the sulfur doesn’t just end up in the northern hemisphere.
Liza Lester: Now you’re narrowing down your questions as to where it might be.
Tushar Mittal: Exactly.
Liza Lester: Etna falls within that possibility band.
Tushar Mittal: Yes. Etna falls within that possibility band.
Liza Lester: Let’s talk about where Etna is. It’s in the Mediterranean. It’s in Sicily.
Noah Randolph-F…: It’s centrally located in the Roman Republic, which is the spacial scale that we actually care about during that time period. If you imagine that the Roman Republic was this diffuse… Morgan I’m sure talks about this… It goes from Spain to Turkey. Most of the agriculture and food is coming from Egypt and Turkey. Etna is dead in the center of that whole republic.
Liza Lester: It’s situated to impact all of the Republic, potentially, depending on the way the wind is blowing.
Tushar Mittal: Exactly. It’s about 800 kilometers from where Rome is. Depending on where the winds are moving, it can either have material either directly going over Rome or it can have material that moves more over the Mediterranean and then cycles back towards Rome and the larger Italy.
Liza Lester: We knew there was eruption at this year because people wrote about it. And we know from the ice core that there was a big eruption somewhere in the world. Why have people not connected these before? Why didn’t they think it was Etna?
Noah Randolph-F…: Some pioneering work in the ’80s had looked at classical sources and looked at these times when people had observed eruptions and had documented bad things happening and tried to go from those from those eyewitness accounts back in history to try to say how big eruptions were. There was a pioneering classic study in the ’80s that said maybe the things that people were seeing in Rome was related to this eruption that people had observed. One reason that I think it’s been difficult in the past to address this problem is that there weren’t a lot of records globally and the resolution and time of those records was quite coarse. A large sulfur anomaly plus or minus 20 years is a lot less easy to attribute than plus or minus one year.
Noah Randolph-F…: These advances in modern proxy records, and new norms about letting data be publicly available, have opened up a whole new world of being able to look at these ancient eruptions.
Isabel Fendley: Also, advances in ice core dating, which is kind of what Noah is getting at. That’s only within maybe the past 15 years that we’ve known exactly when this anomaly happened.
Liza Lester: So you can narrow in. There was a known anomaly but this is getting closer to the when.
Noah Randolph-F…: This is actually one of the big contributions that Rafael made, is that people had speculated that there might be a connection, but we treated that as a testable hypothesis, and that’s also a novel approach.
Liza Lester: Basically they have all of this observational data…like the ice cores and all of that stuff… and then they have the historical information that they have, but they need to put this together, and they do that using a model.
Isabel Fendley: Using a model, yeah. What the model tried to do is look at wind patterns and say, “If a volcano erupted here, would the gasses and particulates go to the right place to have the effects that were observed historically or at the times?” They don’t know where the wind was blowing 2,000 years ago. We didn’t have those weather stations. But we know a lot about our weather over the last century. Basically, they used the wind patterns from the last century and they ran it over a lot of years so that the specifics of that year wouldn’t matter so much to figure out if the gasses would blow over Rome at the right time and would they blow over China at the right time.
Rafael Castro: That’s the basic idea. Obviously we don’t have satellite data or atmospheric data for 44 BCE, so we’re sort of at a loss there, but we do have good data for the past 70 years for the entire globe, which is pretty cool. There’s this huge data set that NOAA has put together… Not Noah.
Liza Lester: Like the N-O-A-A? The atmospheric association? Yeah. That NOAA.
Rafael Castro: Using this, we can pretty much run these models wherever we want and let them run for as long as we want and we’d be able to track these particles around the entire globe. We basically just followed this particle as it’s moving along and see where the wind is moving it and we get a pretty picture that comes out that tells where exactly the particle is and how high it is. If you run this for a ton of years, you can get a good sense for where this eruption would good. Doing it for so many years kind of gets rid of that annual and seasonal variation, so that definitely helps us. Granted, it’s like 2,000 years later, so you could say that the atmosphere had changed a decent amount but on an Earth timescale it’s not that huge of a change. The main thing I’d be worried about would be any post industrial anthropogenic changes because that is the biggest change we’ve seen in the past 2,000 years, is that small few hundred years that we see that huge jump in carbon dioxide. But realistically, I don’t know if that was that huge of an impact.
Liza Lester: It’s reasonable to think that the way the jet stream worked and the way wind is blowing 2,000 is probably similar to assured stuff in geological timescales.
Rafael Castro: I think we picked February 15, because that’s what the eyewitness accounts… The eyewitness accounts generally agree on February 15.
Liza Lester: As the eruption of Etna?
Rafael Castro: Yeah. That’s the day we picked to run it on. We’d start on February 15 every year. There were different runs that we did. Some runs were shorter and had a higher resolution when we wanted to look at the impacts that it had over Rome, and there some runs that we did that were longer where we wanted to confirm that these particles are making it to the north pole and hitting these ice core records. But like I said, it’s every year. We’re not running for 10 years at a time. Every year we’re doing it for a certain amount of time.
Isabel Fendley: Trying different months as well then lets you evaluate what time of year the eruption may have happened, so we’re also testing whether or not it’s consistent with it being a February eruption.
Liza Lester: So by trying different times of year you can get an idea that it looks right based on the data we do have when you start February 15 and maybe not so much if you start May 15 or March 15.
Tushar Mittal: Exactly, because you get different seasonal patterns and that would change the wind patterns.
Liza Lester: But the starting on different years is more to get rid of the variability from year to year in the data that you were modeling from?
Tushar Mittal: It’s because if you’re in San Francisco every February 15 or every December 10 at AGU time there will be generally some kind of weather but depending on if there’s a storm or not the particles will move to different locations. We wanted to look at that and see how different that is. Are we getting completely different answers every year? If that was the case, that would suggest that this constraint is not very strong, versus you saying on average this is the wind pattern and this is the way stuff is going in February. This is where the particles in November, for instance.
Liza Lester: Did you see a lot of variability from year to year?
Rafael Castro: There was a decent amount of variability from year to year. Mostly what I was seeing when I was doing these is trying to see if the scattering would tend towards the east and hit China to create these crop failures that we were seeing in those records, and also Egypt. February and March tended to do that the most and most other months would do some other strange thing is going in different directions. Generally, northeast was the direction, but how strongly that flow is northeast would vary depending on the month.
Liza Lester: Is that reassuring that because you knew Etna had erupted in February… based on historical accounts… this is right. I’m not making things up. Okay. They knew that there was this eruption in February. If you’re seeing the wind patterns for that time of year make sense for the climactic effects on the effects on crops and agriculture seen in southeast Asia and China at the time and in Egypt, it makes sense, versus a summer eruption wouldn’t make sense.
Isabel Fendley: Especially because the ice core record and a lot of the paleoclimate records don’t have that kind of resolution. We can’t say from those records alone what time of year an eruption was or even… in some cases… exactly which year it was. 44 BC works. Maybe 45 does too. Maybe 43.
Liza Lester: And Rafael, what did you see when you ran this model? Where are these particles going?
Rafael Castro: In general, they’re moving towards the east, which is where we’re seeing these effects on the crop yield records. The other thing we were looking for was the height of the particles. As Tushar mentioned earlier, we care about whether or not these particles are making it to the stratosphere because that changes how long they’re up there and what kind of effects they have.
Rafael Castro: An interesting challenge in that was deciding where the stratosphere was, because that changes mostly spatially, so that’s good for us because we don’t have to worry about the time too much. But it was kind of important to make that distinction and say that over Italy the stratosphere generally starts about here.
Liza Lester: So that’s not a set point? It’s not exactly 60 kilometers? How high is the stratosphere and does it move around?
Rafael Castro: It’s not set and it does change. The reasons why it varies are pretty complicated, but in general we have a good sense for where it’s supposed to be spatially. It tends to be pretty high at the equator and it gets lower as you move up. I want to say like 10 kilometers plus or minus five.
Isabel Fendley: The approximate boundary between the troposphere… the lower atmosphere… and the stratosphere… the upper atmosphere… is going to be where most planes are flying. If you taken a plane you’ve flown in that boundary layer.
Liza Lester: Is that because it has to do with the lift that the plane is getting?
Rafael Castro: To my understanding, that’s where it’s the most stable or calm. It’s like that cloud boundary layer and you don’t want to be flying in the mess. The stratosphere tends to circulate peacefully.
Isabel Fendley: That stablish layer is also why it can sometimes be difficult for particles to cross that boundary. That’s one reason why we needed to test that and make sure that the particle distribution was consistent with observations.
Rafael Castro: Just to put it together and paint a full picture, we’re looking for the lower atmosphere particles to linger around the Roman Republic the most and cause effects there on the ground. Then we’re looking for a decent amount of particles to cross over to the upper atmosphere and the stratosphere and travel far enough to cause the crop yield failures that we would see and also cause these effects that we see in the ice core records.
Tushar Mittal: There’s no rain in the upper atmosphere so they can transport farther. That gives us some ideas in terms of geographical location where options need to be if you wanted to cause effects of people living on the ground directly versus if you wanted to have larger optical phenomena and global scale effects.
Liza Lester: What did the eruption at Etna in 44 BCE look like compared to other eruptions we might be familiar with? Was it explosive? I know the effects were recorded in Rome, but that’s pretty far away. What about people closer? Did they see it? Was there a reason to think it wasn’t that big of an eruption? Maybe they were surprised at the effects it had globally.
Noah Randolph-F…: The answer to this is going to be disconcerting and I’m sorry about that. One thing you might ask is how large is an eruption required to change the climate. The way that we measure the size of a volcanic eruption is called the VEI: volcano explosivity index. It doesn’t matter what exactly goes into that, but you can compare the size of an eruption based on the ways that we measure that versus the amount of an effect and the amount of sulfur it puts into the stratosphere, and there’s no relationship. Zero.
Noah Randolph-F…: I think this goes back to this puzzle that you were asking about. I think this is one reason why people have been reluctant to attribute these effects to Etna; there was an eruption at Etna and people saw it and modern geologists can go and put their hands on those rocks. It’s not a lot of rock that was produced. What we do know is that Mount Etna is one of the most sulfur rich volcanoes on this planet. The size of that eruption was maybe not as impressive even as Mount Saint Helens may be today, but its effects were much larger than anything we’ve observed in modern times.
Liza Lester: Like these stealth effects of the invisible gas.
Tushar Mittal: Exactly. If you’re living nearby in Pompeii and Vesuvius ejects a lot of ash, that’s really important for people living in Pompeii and it would look like a big eruption and it might be really disastrous, but that doesn’t mean that will have the same kind of signal globally because it’s a different process. But we think that because Etna is known to have a lot sulfur… When people look at rock from Etna in general and look at the gasses either coming out directly or look at the gasses that are recorded in small capsules in the magma [inaudible 00:59:11] or inclusions of bubbles, you find that it’s very rich in sulfur compared to a lot of other volcanoes. We think that because of that, it may have been much more sulfur rich than a typically eruption.
Tushar Mittal: We haven’t gone and done the work of looking at those deposits yet, and that’s something that can be tested. This is an idea. We’re basically saying, “It’s very consistent with all the effects that are happening and what the records are.” Our hope is that this work would help focus people to go and look at those deposits more carefully, try to quantify it more, and look at those properties to see whether it was as sulfurish as we think it needs to be or was it not?
Isabel Fendley: Sulfur is an invisible gas, however it’s not invisible to satellites. We can actually see Etna emitting sulfur all the time right now from satellites. We know this is a process that’s happening and we know that Etna is an enormous emitter of sulfur.
Noah Randolph-F…: One question of interest is why are we interested in some volcanic eruptions more than others, and it makes sense that Mount Vesuvius is incredibly charismatic. We see the people painfully dying as they’re smothered in ash.
Liza Lester: It’s true.
Noah Randolph-F…: That’s part of why we’re interested in it. It’s very visual and it produced almost no sulfur on record. We have this outsized view of this incredibly small eruption. Similarly, Mount Saint Helens was a small eruptions but it had an effect on people’s lives and that’s why we remember it. Mount Etna in 44 BCE maybe was not quite as charismatic as some of these other eruptions but it had a much larger effect.
Liza Lester: It may be underappreciated.
Noah Randolph-F…: Underappreciated effect.
Noah Randolph-F…: The ancient sources described all of these environmental effects and I think those have been largely discounted by subsequent work, and I think that’s partly because are like, “The Romans are super superstitious and they had all of these weird political biases and made them tell a bunch of lies.” In some ways our work is more in line with ancient sources than the 2,000 years of historical record that have followed.
Liza Lester: We underappreciated their direct reporting on what was happening.
Shane Hanlon: It seems like the way that things were written up in history was reported… reported, sure. It was almost too fantastical or too far out there to be believed. But we should’ve taken this history into consideration and accepted it as truth in some capacity.
Liza Lester: Yeah. I guess you can say that the things that they were reporting that were pretty accurate were hidden among lines that seem more fantastical. For example, we heard that poem earlier about the darkened skies. That sounds pretty realistic, right? There’s this other poet who’s also talking about darkened skies but then the poem takes a funny turn.
Morgan King: This is one of my favorite authors. Tibullus also writes about how the sun stopped shining for this year. [Latin 01:02:36]. “The gloomy year saw the sun itself without light and it yoked its pale horses.” This is the idea that the personified sun isn’t shining any more. Give me a second.
Liza Lester: Are you translating in the moment?
Morgan King: Yes. The second couplet just gets into weird cow stuff.
Liza Lester: So you stick with the first couplet?
Morgan King: Let me just stick with the [inaudible 01:03:33].
Morgan King: They’re close observers of nature. They wanted to read into all kinds of things that happened. When shit hit the fan, they’d look for what they called prodigies: weird things that happened in nature. That could be your cows start talking like humans or lightning strikes a mausoleum or really bad hail or the sun gets blotted out or a cow is born with two heads. All of these things are useful information for understanding where you stand with the gods.
Liza Lester: Godly commentary on what people down here are doing, and they’re like, “Blotting the sky out, maybe we’re not down with these decisions”?
Morgan King: Something is not right, but they also group talking cows in the same broad category.
Liza Lester: That would be surprising.
Morgan King: It’s a bit strange to modern sensibilities.
Shane Hanlon: I don’t know. I wouldn’t mind talking to a cow.
Liza Lester: I wonder what cows think.
Shane Hanlon: Exactly. This is totally believable.
Liza Lester: You can kind of understand why historians looking at this were thinking, “This is all metaphorical.”
Shane Hanlon: Right. They’re not going to piece through the ridiculous stuff to find the kernel of truth in there. I get it.
Morgan King: I’ve been friends with Noah for a long time and we love talking to each other about our research. We both work a lot on things of the past. That’s something that classicists and geologists share in common: that we are both interested in the past. Geologists are often interested in the much deeper past. I thought I knew so much of what there was to know about this period and I hadn’t even stopped twice to think about this eruption.
Liza Lester: Does looking at it from a different discipline’s point of view give you different ideas about the sources you’re studying and what you’re thinking about?
Morgan King: Absolutely. It’s so easy to fall into human dominated narratives of history, and who can blame you? We as humans are fascinated with ourselves. We love the Game of Thrones narratives. I think to take a step back and think about how we would think about these years if we were telling the story not about human agency and maneuvering but about this catastrophic environmental disaster that happened for several years. There’s a very different narrative that you can see in this time period if you look at it from a different angle. And you can even put the humans back into it. As we’re talking about, the lived experience is really different if you’re thinking about it not just like, “My general died,” but, “My general died and now I can’t breathe and I can’t see the sun.” You might ask why Virgil chose to write a four book poem about farming.
Liza Lester: Why did he write a four book poem about farming?
Morgan King: It’s a good question and it’s one that scholars still wrestle with. There are lots of reasons you can talk about, but maybe one reason we could be talking about is that the natural world felt really unstable: that the question of how you make stuff grow in a consistent… and create a stable life and relationship with the land and the world around you felt really tenuous.
Shane Hanlon: If I’m understanding right, Virgil is… Virgil, Virgil, Virgil…
Liza Lester: Virgil, I think.
Shane Hanlon: I don’t know. We’re getting into all kinds of pronunciation things. Virgil is more famous for the poem the Aeneid.
Nanci Bompey: Yeah, I don’t think I read that though.
Shane Hanlon: That’s not one of the things you’ve read? You’re a voracious reader. Would you read his four book poem about farming?
Nanci Bompey: Perhaps.
Shane Hanlon: Would that be one of your desert island reads? We’re going to have to go back and edit one of our podcast episodes to add that.
Shane Hanlon: That’s all from Third Pod from the Sun.
Nanci Bompey: Thanks so much to Liza for bringing us this story and thanks to Morgan, Rafael, Noah, Isabel, and Tushar for sharing their work with us.
Shane Hanlon: This podcast was produced by Liza and mixed by Kayla [Surrey 01:08:19].
Nanci Bompey: We’d love to hear your thoughts on our podcast. Please rate and review us on Apple Podcasts. You can find us there or wherever you get your podcasts, and of course always at thirdpodfromthesun.com.
Shane Hanlon: Thanks all. We’ll see you next time.
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