Tyler Cohen posts on some plausible scenarios in which nuclear weapons might be used in the near future with the caveat putting "aside dirty bombs from terrorists and the like."
After analyzing the situation, he plausibly discounts the likelihood of nuclear weapon being used in a Pakistan-India conflict, but does identify two scenarios which a nuclear exchange might take place:
1. North Korea threatens to use nuclear weapons if its demands are not met, its bluff is called, and it nukes a second tier Japanese city. He reckons that North Korea would fear retaliation if it attacked China, and might not want to bomb fellow Koreans in South Korea. Fear of retaliation and fear of a technical dud that would reduce its credibility might also discourage a strike on the U.S.
2. I'll let Cohen set out his second scenario:
[T]he United States and China are fighting a naval battle in the South China Sea, or perhaps further north, as part of a limited exchange, not a full war. The United States is about to win the battle, and the Chinese leadership fears a military or other Party-based coup in response. So they use nuclear weapons, perhaps tactical nukes, to turn the tide in the battle and save their skins. They figure the U.S. won’t respond with a full-blown nuclear war. (America, if it lost a comparable naval battle, is more likely to just turn tail and run, at least in the short run.) . . .
My core model, by the way, is that political leaders are rational in the loose sense. So if you are looking for instances of possible nuclear weapons use, consider cases where politicians might be facing relatively dramatic “career-ending” events if they lose a smaller-level struggle.
There are some scenarios that Cohen doesn't consider that I think are also plausible:
1. Suppose that Iran has come to the verge of having usable nuclear weapons and has rhetoric suggesting that it would use them against Israel. Israel might strike preemptively with its own nuclear weapons.
2. Trump uses nuclear weapons in a less than rational decision to deal with ISIS or Islamic terrorism more generally. This could take the form of a nuclear weapon on Raqqa, its capitol, or could involve the threat frequently invoked in right wing rhetoric of bombing Mecca.
3. There is a non-negligible possibility that China could use its own nuclear weapons against North Korea. As I've noted previously at this blog, there is no one who would ally with North Korea in a military conflict with China, China has a variety of internal reasons to demonstrate its military clout for internal political reasons, and North Korea's leader has no sense that he has bounds on his own conduct that can't be crossed so he could easily go overboard in provoking China at some point. For example, if North Korea threatened credibly to use nuclear weapons against "someone" and then refused to clarify that China wasn't on the list of potential someone's even if it was far from the top of North Korea's target list, China might make a preemptive strike against North Korea.
I do think that a Trump Presidency reduces the likelihood of a nuclear exchange between Russia and the United States over expansionary actions by Russia in the Pacific, or sparring between patrols in neutral territory between Russian and U.S. forces. Trump and Putin are on good enough terms that they would negotiate to resolve the situation and that Trump would back off from the defense of its allies if Russia tried to reclaim territory in Eastern Europe. This may be good news for the future of the survival of the planet, but this news is bleak if you are a newly independent Eastern European nation and want to stay independent.
Indeed, in a nutshell, the circumstances where a nuclear exchange might occur involve situations where the logic of mutual assured destruction (MAD) that prevented a nuclear war between the U.S. and the Soviet Union during the Cold War have broken down. The party using a nuclear weapon might plausibly imagine that they will not be nuked off the planet if they do so, and might even imagine that using a nuclear weapon was the only way to defend itself from an imminent nuclear attack from the target.