Volcanic eruptions in the Northern Hemisphere may have contributed to unrest and conflict in ancient Egypt, according to a study published in Nature Communications.
The interdisciplinary research combines paleoclimatology—the study of past climates—with historical analysis to examine how environmental stress influenced the economy, political stability, and military capacity of ancient Egypt. Researchers from Yale University and other institutions investigated how volcanic activity may have disrupted the natural systems on which Egyptian society depended.
Large volcanic eruptions release particles into the atmosphere that reduce incoming solar radiation and temporarily cool global temperatures. The study shows that such cooling in the Northern Hemisphere likely weakened the African monsoon, which reduced rainfall over the Ethiopian Highlands.
Because the Nile River relies heavily on monsoon rainfall in East Africa, weaker monsoons meant lower water levels in the Nile. This had serious consequences for ancient Egyptian society, which depended almost entirely on the river’s annual flooding to sustain agriculture.
To explore these links, the researchers combined several types of evidence. These included climate models of major 20th-century volcanic eruptions, historical measurements of Nile summer flood levels recorded by the Islamic Nilometer between 622 and 1902, and descriptions of Nile flood conditions preserved in ancient papyri and inscriptions from the Ptolemaic period. Together, these sources show that large volcanic eruptions were associated with reduced Nile flooding during the agriculturally critical summer season.
“Ancient Egyptians depended almost exclusively on Nile summer flooding brought by the summer monsoon in East Africa to grow their crops. 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,” said Joseph Manning, lead author of the study and the William K. & Marilyn Milton Simpson Professor of History and Classics at Yale.
Ice cores recovered from the Arctic show spikes in sulfur deposits that suggest at least two major volcanic eruptions occurred in 46 and 44 BCE. These eruptions may have contributed to environmental conditions that intensified social and political instability during the Ptolemaic Kingdom.
The Ptolemaic Kingdom, which ruled Egypt from 305 BCE until 30 BCE, experienced repeated native uprisings as well as foreign and civil wars. These conflicts weakened the kingdom and eventually culminated in its annexation by Rome.
Reference:
Ludlow et al. “Volcanic suppression of Nile summer flooding triggers revolt and constrains interstate conflict in ancient Egypt.” Nature Communications, October 2017. DOI: 10.1038/s41467-017-00957-y.