When you guys are talking about Nuclear events occurring, a lot of you are forgetting about the Nuclear Winters that follow the event of a Nuclear explosion. You guys make it seem like the explosion and radiation are the only things to worry about. Not only will a Nuclear Winter kill off plant life, etc., it can and would kill us off depending on the quantity of Nuclear Weapons that exploded.
Now, there is also something called a Volcanic Winter, which is very similar to a Nuclear Winter, however, it occurs after the eruption of a Volcano.
Say, if Yellowstone were to erupt, (I live within a few hundred miles of it, actually), the thing that would end up eradicating us all would be the Volcanic Winter that follows the eruptions. Yes, the eruptions would decimate everything in a certain area. I've read that up to 2/3 of North America would be completely un-inhabitable and all the food supplies, etc. would be completely wiped out. I've also read that the entire Northwest region of North America would be completely destroyed. I've also read that areas within 1,000 miles away will be covered in up to 10 feet of volcanic ash.
A Volcanic Winter from Yellowstone would be completely devastating, maybe more so than a Nuclear War. It depends, though. If suddenly half of the nukes in the world were to explode, that would probably be far worse than Yellowstone.
Just my 2 cents..