On the volcanic eruption that set an ominous stage for the death throes of the Roman Republic.
The Romans were great believers in omens, and an event as world-shaking as the assassination of Julius Caesar was apportioned its predictable share of signs in the collective memory. The year of his death seemed to start under hopeful auspices. To the Romans, who named their years after the highest officials in the res publica, what we call the year 44 bc was the year when Julius Caesar and Mark Antony were consuls. There are hardly two more eminent names in the annals of Roman history. Julius Caesar was then at the height of his powers, and the award of the consulship to Antony signaled a full reconciliation with his faithful lieutenant after a brief chill. For a moment it must have felt as if there were order in the cosmos. Grand new campaigns of conquest were rumored. But resentment simmered among the old-guard senatorial faction that Caesar had brought to heel. And soon disturbing portents began to appear.....MUCH MORE
The ancient biographer Suetonius gave a summary catalogue of these signs and warnings. A kingbird (avis regaliolus) was savagely ripped to pieces in the Theater of Pompey. Horses that Caesar had dedicated to the river Rubicon refused to eat and wept instead. A bull sacrificed to the gods was found to be without a heart, and the presiding priest duly warned Caesar that he was in imminent danger. Bad dreams and rumbling heavens followed. Shakespeare, with a dash of poetic license, immortalized these forebodings: “Beware the ides of March.” On March 15, 44 bc, Julius Caesar was hacked to death by his jealous political rivals, plunging the Romans once more into the nightmare of civil war.
On the death of Caesar, even the sun disappeared. And it did not just disappear for a passing moment, as in a normal eclipse. Befitting the demise of the larger-than-life Caesar, the sun absconded for a year. On this point the Roman sources are unusually insistent and coherent. According to Pliny the Elder, writing a century after the fact, “portentous and protracted eclipses of the sun occur, such as the one after the murder of Caesar…which caused almost a whole year’s continuous gloom.” Plutarch was even more vivid in describing “the obscuration of the sun’s rays”:
During all that year its orb rose pale and without radiance, while the heat that came down from it was slight and ineffectual, so that the air in its circulation was dark and heavy owing to the feebleness of the warmth that penetrated it, and the fruits, imperfect and half-ripe, withered away and shriveled up on account of the coldness of the atmosphere.It is easy enough to dismiss these observations as the superstitions of a prescientific age. We might attribute them to the human mind’s infinite ability to imagine connections where there are none, or more generously, we could try to understand these reports as culturally meaningful texts, a symbolic language through which the Romans experienced the world. But thanks to unexpected insights and data gained from our own urgent need to understand the earth’s climate, we have learned that there is much more to the story of the celestial signs that followed Caesar’s death.
In the August 1983 issue of the Journal of Geophysical Research, two scientists from NASA’s Goddard Institute for Space Studies, Richard Stothers and Michael Rampino, published one of the most remarkable pieces of interdisciplinary history ever written: “Volcanic Eruptions in the Mediterranean Before ad 630 from Written and Archaeological Sources.” Their project of assembling a catalogue of historic earth events was nothing revolutionary in itself; Stothers and Rampino built on centuries of work by geologists to collect references in the literary record. But what made their contribution so thrilling was their insight that many ancient reports of volcanic eruptions and other atmospheric anomalies could be correlated with a new kind of historical evidence: ice cores from Greenland.
The progressive buildup of knowledge about how the climate system works has been painstakingly achieved by the collective and incremental enterprise of earth science. Paleoclimatology is an integral part of this enterprise, and there is no understanding where the climate is going without understanding where it has been. And ice cores are one of the most important records of the past climate. These sleek columns hoisted from the ice sheets are a kind of natural archive: frozen texts written in the language of geochemistry.
Even though human-driven climate change has pushed us to the edge of a perilous new epoch known as the Anthropocene, the earth’s climate has always varied and changed. Though this fact is often gleefully trotted out by climate-change skeptics, in reality our understanding of the present peril is framed and sharpened by our knowledge of the climate’s turbulent past. The causes of natural climate change are many. Gradual oscillations in the tilt, spin, and orbit of the earth change the amount and distribution of solar energy reaching the surface of the planet. The sun itself is an inconstant star; the eleven-year sunspot cycle is only one familiar example of its variability. But among the natural causes of climate forcing, volcanoes hold a special place. Nothing else can trigger such short-term and violent climate anomalies. And almost nothing leaves such a distinct and potentially decipherable time stamp on the ice records.
Large volcanic eruptions inject massive amounts of sulfur dioxide into the stratosphere. While heavier ash particles fall quickly back to earth, sulfur gas is aerosolized. The fine suspensions stay aloft in the stratosphere for years. Diffused by the stratospheric jet stream, they can unfurl across one or both hemispheres, depending on the location and timing of the volcanic eruption. This veil of sulfate aerosols scatters solar energy, causing rapid cooling. If carbon dioxide is like a blanket that holds in the earth’s heat, volcanic sulfur aerosols are like the foil reflector you put behind your car’s windshield. The effects can last for years, but eventually gravity wins and pulls the particles down. Some of the volcanic ejecta ends up falling in the snow that settles quietly on Greenland’s ice sheets, where it is packed in annual layers that record the history of the earth’s atmosphere....
