End of the Green Sahara: North African Desertification

The African Humid Period that had sustained lakes, rivers, and savanna vegetation across the Sahara since approximately 9000 BCE ended as Earth's orbital precession shifted the West African monsoon southward. Weakening summer insolation over North Africa reduced moisture transport from the tropical Atlantic, triggering vegetation-albedo feedbacks that accelerated drying. Human pastoralist communities that had occupied the region for millennia migrated toward the Nile Valley, the Niger bend, and Lake Chad.