Short of a nuclear conflict or CME, another potential threat is a meteor, asteroid, or comet impact. The Chelyabinsk meteor of 2015 is a wake up call.
Here's an interesting effects calculator-
https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/
Here's an interesting effects calculator-
https://impact.ese.ic.ac.uk/ImpactEarth/ImpactEffects/