What survivable events would make Earth least inhabitable?

I am interested in events that would so radically change Earth (for the worse) that it would be near uninhabitable for humans. The event may or may not be deadly to humans, but the world it leaves behind should be a very hard one to live in.

Note constraints:

• Anthropogenic events must be based on current science/technology (e.g. no AI overlords making humans wash their metallic feet)
• Natural events can be unlikely, but must be possible (e.g. "The Earth spontaneously blows up" is not a valid answer)
• The event must be survivable both immediately and long term, even if the chances are very slim. It's fine to get creative but the means of survival must fit present or near-present technology levels.

I would expect a good answer to consider what would be entailed in surviving on Earth during/after the given event and how unlikely success is. There is certainly more than one answer to this, but the one that leads to the lowest chances of survival for humanity will be the correct one.

posted over 5 years ago

ben‭

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