Science

How climate stress triggered by an Alaska volcano contributed to the collapse of ancient Egypt

Okmok Caldera

Egypt’s rulers say they fear the effects of climate change on their society. They have good reason to worry: Their ancient predecessors were probably toppled at least in part by similar climate challenges, researchers say.

Historians and climate scientists have tied droughts and other climate disruptions to political upheaval in Egypt’s Ptolemaic era more than 2,000 years ago, using the unusually well-preserved records of the Nile River to draw a line connecting climate challenges and social turmoil.

The research can’t be used to predict the fate of modern-day societies as they grapple with a warming world, but it is a measure of the stakes as Egypt hosts this year’s U.N. Climate Change Conference. Pakistan and Ethiopia were hit by deadly floods, Somalia is facing a devastating drought, and Europe had its hottest summer on record. Ancient Egypt was wealthy and powerful - until it succumbed. Modern societies face some of the same challenges of adaptation.

Cleopatra

In the Ptolemaic era, which started around 300 B.C. and ended with Cleopatra’s suicide and conquest by Rome in 30 B.C., settlements and societies that figured out how to make themselves more resilient to climate stress - such as by storing grain to help smooth out “hungry seasons” - proved more stable, the researchers say. But climate pressures probably proved too much for the Egyptians: The eruption in 43 B.C. of Okmok volcano in Alaska’s Aleutian Islands - on the other side of the world from Egypt - was so profoundly disruptive to the world’s climate systems that it led to crop failures and disease across the Mediterranean region. Ultimately, the challenges probably contributed to Cleopatra’s downfall, the researchers say.

“We know from a societal point of view, these were really stressed-out periods,” said Joseph Manning, a historian at Yale University who has led a multiyear effort to study the relationship between volcanic eruptions, Nile flooding and historical societal response.

[Climate change threatens ‘things Americans value most,’ U.S. report says]

Ancient Egypt wasn’t facing man-made climate change in the way modern societies are. But the eruptions produced climate disruptions similar to some aspects of contemporary climate change, and they challenged ancient societies to respond in ways that are analogous to modern efforts. (There doesn’t appear to be an ancient equivalent to U.N. climate conferences, though.)

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Then as now, climate stress was often a crisis magnifier, eroding social resilience and making it harder to deal with other challenges successfully. Even if climate issues weren’t the sole reason for Egypt’s ultimate defeat by Rome, social cohesion - and military might - had been worn away by years of bad crops and disease following the volcanic eruptions.

“What we’re seeing in a pretty clear way is the complexities of societal response, and this kind of climate shock - these kinds of year-by-year short-term droughts - is one of many aspects of societal stress,” Manning said.

The researchers focused on the Ptolemaic Kingdom because, although its measurements of the Nile weren’t as precise as those of later societies in Egypt, it did leave an extensive written record, including many papyruses that can be tied to specific dates with a reasonable amount of confidence. The kingdom - the last ancient Egyptian dynasty - rose in the years following the death of Alexander the Great in 323 B.C., and at its maximum extent ruled over most of modern-day Egypt and parts of modern-day Libya, Israel, Jordan, Lebanon and Syria.

Manning and his team of historians and scientists, including Francis Ludlow, a historical climatologist at Trinity College Dublin, matched records of volcanic eruptions from ice cores in Greenland and elsewhere with measurements of the Nile’s seasonal flooding over hundreds of years.

The core samples give down-to-the-year readings on major volcanoes, whose clouds of ash can travel around the world and dim the sun, altering the climate by cooling it. The eruptions can also lead to less rainfall, doubling the impact on food production. The researchers found that eruption-year summer flooding averaged 8.7 inches lower than in normal years.

Researchers were able to connect a rise in descriptions of stress, disease and other societal challenges to years following ones in which the Greenland ice data showed there had been a major volcanic eruption.

In their first paper, published in Nature Communications in 2017, they noted significant increases in land sales in periods following eruptions, for example, which Manning and his team theorized were connected to a need to raise money to pay property taxes during years in which farming wasn’t bringing in as much money. Wars were more likely to end in a volcano year or the year following an eruption, suggesting to the researchers that societies may have had difficulty continuing to fight during years in which their resources suddenly faced major constraints.

There were major eruptions in 247 and 244 B.C., for example, a time in which Ptolemy III was away from home, engaged in a successful military campaign in what is modern-day Iraq. Ptolemy’s Roman contemporary, Justin, a historian, notes that the ruler was “recalled to Egypt by disturbances at home.” A later papyrus echoes the idea that Ptolemy was recalled home to face “Egyptian revolt” around that time, the researchers write. And a priestly decree from 238 B.C. is explicit about lower-than-usual Nile floods in the previous years and notes that Ptolemy imported grain from other territories “at great expense.”

Manning said the team of researchers has built out its database of writings from the Ptolemaic Kingdom, working to categorize them so that they can be compared quantitatively against the volcanic record.

More recently, Manning’s team has looked at the events around the fall of Cleopatra in 30 B.C. Alaska’s Okmok volcano explosion led to years of problems for the Nile River system, the historical record shows, as well as crop failures and disease. Some sort of plague broke out in the early 40s B.C., Manning said, that was likely tied to the climate challenges.

In a paper in the Proceedings of the National Academy of Sciences, the team estimated that the two years after the volcano exploded were “among the coldest years of recent millennia in the Northern Hemisphere” - as much as 7 degrees Celsius, or 14 degrees Fahrenheit, below average in some seasons.

“We know what happens historically in droughts,” he said. “You get people drinking bad water and you get things like dysentery.”

Cleopatra ultimately failed for a mixture of reasons, he said, including political ones that had nothing to do with the climate.

“But the climate and the disease story is giving us something more of a dynamic of these complicated societies,” Manning said.

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