The Younger Dryas represents the kind of climate shock that would fundamentally dismantle modern civilization. Within the last 250,000 years, Earth has cycled through four major glacial-interglacial periods, each one punctuated by extreme variability. The previous interglacial, the Eemian, lasted roughly 12,000 years and experienced multiple sharp temperature spikes and drops, events that reshaped ecosystems and forced human populations to adapt or perish. The Younger Dryas itself stands out as one of the most abrupt and severe climate reversals in the geologic record. If a comparable event occurred today, with the same speed and magnitude, the infrastructure, agriculture, and supply chains that sustain billions of people would collapse. We would quite literally be returned to Stone Age conditions, not because of nuclear war or societal failure, but because the climate system itself can shift with terrifying speed.