> We could not end Earth's ability to support life even if we tried our best at it

We’re within a few decades of a global superpower being able to deflect a large asteroid which would, after millennia or even centuries, impact the Earth with enough energy to melt the crust several kilometres down.

Not even with all-out nuclear warfare?

> Not even with all-out nuclear warfare?

We don't even have enough nukes to wipe out the human race, let alone the biosphere. Building enough to would likely need more uranium than we can access with known technology.

That's ... the opposite of what I was taught in History at school, but I'm no expert at this.