Would a nuclear exchange unleash enough smoke to cool the climate, creating a "nuclear winter"?
"So here we get into the meat of the question. We know with pretty good certainty how a given amount of smoke in the atmosphere, distributed a certain way, will affect the climate and for how long; but what we can only guess at is how much smoke is produced when a city burns after a nuke. Our guesses are educated, but they're all over the map. Cities also vary wildly in just about every relevant aspect. Let's look at what we know from history."
"So here we get into the meat of the question. We know with pretty good certainty how a given amount of smoke in the atmosphere, distributed a certain way, will affect the climate and for how long; but what we can only guess at is how much smoke is produced when a city burns after a nuke. Our guesses are educated, but they're all over the map. Cities also vary wildly in just about every relevant aspect. Let's look at what we know from history."