On what basis do you make this statement "Even nuclear war isn't a threat to species survival, you could detonate thousands of nukes simultaneously and it wouldn't come close to killing us off."
It estimates that a nuclear war in 1988 would have dropped world population from ~5 billion to ~3 billion (this includes estimates of death due to famine etc).
You can argue with each individual estimate, but it's hard to argue that a nuclear war would actually kill off the human race.
(As noted elsewhere, you can argue that it would be possible to kill off the human race if someone with control of a super-power nuclear arsenal tried to do it. That's a different argument, because you'd have to discuss the likelihood of that circumstance occurring)
Accoridng to http://en.wikipedia.org/wiki/Tsar_Bomba, Tsar Bomba was over 1400 times as powerful as (Hiroshima+Nagasaki), and that was not even remotely close to killing us of.
Thousands of modern devices would be different in many ways: bombs would likely be more powerful on average than the '45 ones, but they could also be cleaner, and they would likely not be used all in the same place. I would guess the species would survive it, if only because the ones starting it would likely be in a good shelter.
Saying that they'd likely be more powerful on average than the '45 ones is a huge understatement. Fat Man was 20 kt, every Trident II missile can carry 12 475 kt warheads. Also, if you distribute nuclear explosions across the world, it's much different than having one meganuke in terms of its effect. Meganukes are very inefficient with their power due to the diameter of an explosive sphere relating to the cubic root of the power. I think the original commenter is way off in their proclamation that we couldn't nuke ourselves to extinction.
It also created a shock wave measured at over 5 on the Richter scale, despite being detonated 4km above the Earth, that travelled at least three times around the globve. What would it have done if it had been detonated at touch down. What would happen if you detonate 10 of those at the same time?
I think it would take worse than that to kill the species, but our civilization is more fragile.
I agree about the civilization part, but this was about the huge gray area between "surely to not make homo sapiens extinct" and "surely to make homo sapiens extinct".
I am an optimist, so I keep thinking that 'we' would survive. I also think we will not be that stupid to do that 'experiment'.
