Six months of food reserves stand between global civilization and collapse if agriculture shuts down. That number isn't speculative, it reflects how tightly coupled modern food systems have become to uninterrupted growing seasons. A volcanic winter or cosmic impact winter that disrupts photosynthesis for even one or two years would trigger cascading failures across supply chains that have no backup. Half the global population could be gone within a year, not from the event itself, but from what follows when the food runs out.
This isn't doom mongering, it's arithmetic. The historical record shows us what happens when climate shifts abruptly and harvests fail. The difference now is scale. We've built a system optimized for efficiency, not resilience, and that makes us more vulnerable than we've ever been to the kinds of disruptions that have happened before and will happen again.