How could Earth's atmosphere become unable to sustain life?

In a story I am (at least attempting) to write, I plan to have Earth's atmosphere become unlivable by humans. I assume that Earth's atmosphere could not be ignited by a solar flare event, because it doesn't have enough oxygen or other flammable gases for this to happen.

Some other possible causes for Earth to be uninhabitable:

1. Extreme global warming - Extreme global warming could possibly render Earth's atmosphere inert. This may be slightly less extreme, as it would only fry to ozone layer, as opposed to completely destroying the atmosphere.
2. Nuclear winter - Basically the opposite of global warming. Could I provide any explanation as to how this impacted the atmosphere?
3. Nuclear war - Multiple nukes detonated high up in the atmosphere could render the atmosphere breathable. Clarification needed.

Any refutations or concessions as to why any of these ideas above might not work?

How might Earth's atmosphere become unlivable?

posted over 8 years ago

QuiquÈ…‭

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