I don’t think nuking NK would have a global effect. No doubt, even such a small nuclear exchange would have dire effects that would last quite some time, but the global cooling scenario is based on a Soviet-US full scale exchange and is in itself a hypothesis.
What is not mere hypothesis is the consequence of letting a nuclear strike happen without nuclear retaliation. MAD exists because it makes nuclear war unthinkable. If the likely US response to a North Korean nuclear strike is conventional war, then future madmen might think, “My military can stand up to the US, so I can do this!” If there’s one nuclear strike that goes unpunished by genocide, then there will be a second, and a third. Nuclear war will go from unthinkable to merely Something Bad That Happens From Time to Time, like 9/11.
Good lord, here we go again. Please read about the actual size of the warheads we have now, and the actual spread of deadly fallout from using those sort of warheads in likely scenarios and such. There would not be radioactive death clouds spreading to any of those countries, and there would not be large areas we couldn’t farm for generations to come.
A lot of the popular mythology about fallout and large scale effects primarily have to do with projections based on the absolute largest warheads ever made, some of which were never even fitted to ICBM and were only detonated experimentally. These are the multiple megaton bombs, and they also posit surface detonation which throws up large amounts of earth as fine particulate (and irradiated) matter. A detonation a few hundred feet above the target destroys all living things in the ground zero area (essentially) and a large circular area around that, but it doesn’t create nearly the fallout popular fiction might lead you to think. That’s actually how we detonated the bombs over Hiroshima and Nagasaki, they were low-altitude detonations, not surface detonations.
The response would not be about North Korea or strategic concerns relating to North Korea. It’d be about Iran, it’d be about other countries that will likely get nuclear weapons in the next fifty years. It’s also got nothing to do with “emotional desire for bloodlust”, militarily toppling the North Korean regime would likely kill just as much, if not more, people than a series of targeted nuclear strikes. What we know from history is the only countries willing to use nuclear weapons are those that believe they can be used without retaliation. If we had to fear a counterattack, we probably wouldn’t have used them on Japan. Using nuclear weapons was also contemplated by the United States during the Korean War, because the USSR was just barely nuclearized at that point and it was not seen as likely that they’d start a nuclear exchange over us using nukes on North Korea. In fact at that point, before both sides had massive world-killing stockpiles, it was expected that nuclear weapons would develop into weapons that had some tactical, battlefield use, as we’re talking very early times in the 1950s. Truman basically decided not to because he didn’t want to set the precedent of being too free in the use of the weapon, and he was also lead to believe it might cause various problems given the presence of American soldiers in the vicinity. But we only contemplated it seriously because we had no fear of a like response. Once it was obvious a few years later the USSR would be willing to use nukes on us in various scenarios and we’d be willing to do the same with them, neither power seriously contemplated deliberate nuclear strikes again.
Something to keep in mind is almost our entire nuclear arsenal (at least that I’ve heard publicly spoken of) is made up of sub-500kt weapons, with a large number in the 100 kt range. A lot of the cases where we had significant fallout during nuclear testing were > 1 Mt nuclear tests done before the dangers were understood. We had some early tests in the United States that resulted in small amounts of fallout blanketing the entire country. While people would go ape shit about that now, the actual health effects were nil, it just wasn’t enough radiation exposure to matter.
There are some studies released on the effect of hitting some dozen or so important hardened military targets in the Moscow area with a barrage of 48 W76 warheads. The result of these detonations was projected to kill just under 3m civilians out of around just under 9m in the area. The fallout effects were projected to lead to direct death/injury as far away as 23 km from Moscow. (Based on wind by the way, 23km is how far it would affect people downwind of the detonation, people upwind would be spared the fallout at much closer distances.) So no, there’s genuinely no concern about a few nukes being used against North Korea causing problems for China, Japan…or even South Korea unless it was right on the DMZ.
During boost stage their missiles are shot down and the NK military is urged to remove their crazy leader in lieu of seeing all their loved ones incinerated in a rain of nuclear hell. Plus we will give them cookies. Not the cheap kind but the good ones with macadamia nuts.