Michael Marshall in Nature:
The missing earthworms were a sign. As archaeologist Harvey Weiss and his colleagues excavated a site in northeast Syria, they found a buried layer of wind-blown silt so barren there was hardly any evidence of earthworms at work during that ancient era. Something drastic had happened thousands of years ago — something that choked the land with dust for decades, leaving a blanket of soil too inhospitable even for earthworms.
The drought hit in roughly 2200 BC, when the Akkadian Empire dominated what is now Syria and Iraq. By 2150 BC, the empire was no more. The central authority had disintegrated, and many people had voted with their feet, leaving the region. The overlap between an epic drought and the collapse of the Akkadian Empire was no mere coincidence, according to Weiss, an archaeologist at Yale University in New Haven, Connecticut. When he and his colleagues discovered the evidence of drought in the early 1990s, they proposed that the abrupt climate disruption had brought the ancient empire down1. This example has become a grim warning of how vulnerable complex societies can be to climate change.