HISTORY LESSON

A study shows how ancient Egypt struggled with drastic changes in the climate

Ptolemaic Egypt—which existed in the years 305-30 BC—was uniquely dependent on the seasonal shifts of the Nile, which in turn made them particularly susceptible to any significant changes to the cycle and mores of the their environment.

Researchers at Yale released a study this week in the journal Nature Communications that, for the first time, correlated ancient environmental events to the recorded political and economic consequences those events had on the stability of culture and society.

Though not yet subject to the greenhouse effects of modernity, ancient Egypt in that period—roughly the time between the death of Alexander the Great and the Roman invasion—the world saw more than a few high-altitude volcanic eruptions. “With volcanic eruption dates fixed precisely in time, we can see society in motion around them,” said Joseph Manning, lead author on the paper and a professor of history and classics at Yale.

Large eruptions eject particulate matter high into the stratosphere which in turn shades the earth, reduces the evaporation of water, lessens rainfall, and reduces seasonal flooding upon which agriculture depends. This effect can last just one season or a few years.

Researchers cross-referenced the meticulous records of Ptolemaic Egypt—one of the reasons the studies authors picked this period to study—with 20th-century climate modelling, with ice-core-based volcanic sourcing data, then again with the Nile summer flood heights as recorded by the longest continuous record of seasonal shift in history—the Islamic Nilometer. “It is very rare in science and history to have such strong and detailed evidence documenting how societies responded to climatic shocks in the past,” said Jennifer Marlon, research scientist in the Yale School of Forestry & Environmental Studies and co-author of the study.

When it was all said and done, volatility in the Nile caused by environmental shifts show a strong correlation with revolts, constrained expansion, and multiple socioeconomic and political hardships. “In years influenced by volcanic eruptions, Nile flooding was generally diminished, leading to social stress that could trigger unrest and have other political and economic consequences,” according to Manning.

While the authors urge caution in attributing the societal events purely to environmental causes, they do find that these environmental shocks played a large role in the uncertainty of the time.

With the exception of the Mount Pinatubo in the Philippines in 1991 there hasn’t been an eruption of this magnitude in recent memory; our current environmental volatility is one of our own making. But as our world warms, the weather will become more unpredictable, something already playing out with years of historic heat, seasons of unprecedented storms, and record droughts.

This first-of-its-kind collaboration between researchers in different fields provides a firsthand historical look at how forces of nature can impact complex social systems, and maybe teach us something about how to handle our own uncertain future.

Correction: Mount Pinatubo is in the Philippines, not Indonesia.

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