Science reports:

For ages, the shadow of a volcano has hung over the fall of the Roman Republic. Ancient historians told of the Sun’s mysterious disappearance after Julius Caesar’s murder in 44 B.C.E., which was followed by bouts of cold and crop failures. Now, a team of scientists and historians has discovered that one of the largest known eruptions in history struck in 43 B.C.E.—potentially contributing to 2 years of weird weather and famine as the republic dissolved and the empire took shape.

The darkened sky after Caesar’s assassination on the Ides of March was likely caused by a known, small eruption at Mount Etna. But early the next year, in January or February, Alaska’s Okmok volcano in the Aleutian Islands blew its stack, forming a giant, 10-kilometer-wide crater rim. The volcano’s northern location meant that sunlight-blocking particles could rise into the low-lying Arctic stratosphere, where they would spread easily throughout the Northern Hemisphere, the researchers report in a new study, published today in the Proceedings of the National Academy of Sciences. “We can absolutely say this volcanic eruption generated extreme climate,” says Joseph McConnell, a glaciologist at the Desert Research Institute and the study’s lead author.

If the eruption did indeed contribute to famine and other disruptions, it could have helped the Roman Empire consolidate its control, McConnell says. “The end of the republic happened during these two extreme years of climate,” he says. “It’s a possible coincidence, but it doesn’t seem likely.”

Some scholars are skeptical and point out that the republic was on its way out well before the eruption. Caesar crossed the Rubicon in 49 B.C.E., precipitating the Roman civil war; 5 years later, he was named dictator for life. “The problems with the republic were political, deep in origin, fought out between members of the elite, not a popular revolution or a subsistence crisis,” says Guy Middleton, an archaeologist at Charles University. And, although the dating and identification of the eruption look undisputable, the evidence supporting the volcano’s climate impact is thin, especially for the Mediterranean, says Kevin Anchukaitis, a paleoclimatologist at the University of Arizona,. “From the little data we have, the local climate story might be a bit more complicated.” [Continue reading…]