Lost Cities and Climate Change
Some people say “the climate has changed before,” as though that should be reassuring. It’s not
By Kate Marvel on July 29, 2019
blogs.scientificamerican.com
excerpt:
Not far from my grandmother’s house is a ghost city. At Angel Mounds on the Ohio river about eight miles southeast of Evansville, there are a few visible earthworks and a reconstructed wattle-and-daub barrier. There is almost nothing left of the people who build these mounds; in a final insulting erasure, the site is now named after the white settler family who most recently farmed the land.
There are traces of other dead villages along the Ohio and Mississippi rivers, mounds scattered from present-day Indiana to Arkansas and Alabama. In southern Illinois, a few miles from the Missouri border, hidden among empty corn and soy fields, is the center of that dead civilization’s gravity: the lost city of Cahokia.
Cahokia was larger than London, centrally planned, the Manhattan of its day. Most people there would have come from somewhere else. There were defensive foundations, playing fields, and a magnificent temple. There would have been sacred ceremonies and salacious gossip. It must have been a very exciting place to live.
And then, relatively abruptly, it ceased to exist. We know of the city only because of the physical traces left behind. Few stories of Cahokia have survived; it disappeared from oral tradition, as if whatever happened to it is best forgotten. The archaeological record shows traces of the desperation and bloodshed that almost always accompany great upheavals: skeletons with bound hands, pits full of strangled young women.
The North American Drought Atlas, a historical record of climate conditions pieced together from the rings of old trees, provides a hint of what might have happened. The tenth century CE, when the Cahokia civilization would have developed, marked a distinct shift in the regional climate from persistent drought to rainier conditions more suitable for agriculture, centralization, and civilization.
But the good times were not to last. In the middle of the fourteenth century, the climate swung back toward drought. This shift was likely associated with shifting temperature patterns in the ocean that affected the jet stream, pulling cool air down from the Arctic and displacing rainfall patterns. These changes are attributable to some combination of natural internal climate variability and externally forced changes from solar activity and increased volcanic eruptions. Their effects were profound.
In Europe around the same time, a confluence of natural factors perhaps related and perhaps separate from the forces drying out the Mississippi Valley caused it to rain heavily in the summer of 1314. The rains continued into the winter, and then into the next year, and then the next. Crops rotted in the fields, and the entire continent went hungry. Contemporaneous historical records complain of rain and famine, villages forced to eat dogs and cats, the dead, and even each other.
The Old World Drought Atlas, a collection of European and Mediterranean trees, shows a period of persistent wetness around the beginning of the 1300s that corroborates these historical accounts. Many of us unwittingly remember the famines in the stories we tell our children. The fairy tale of Hansel and Gretel—hungry children abandoned in a forest haunted by a cannibal witch—almost certainly dates from this time.
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