I'm highly skeptical that this conflict would go nuclear. It's unfortunately always a possibility, and people, especially Amerikkkan imperialists nutjobs, can and will do stupid things without thinking about the actions of their consequences, but my two-fold thinking is that not only is nuclear-war really unlikely to happen (or way less than most people think) I think it would very likely also be less destructive, depending on how things go.
People always imagine that in a nuclear war scenario, all bets are off, but I don't think so. There is usually some sense, even in chaos.
Most or all of the most devastating nuclear weapons were disarmed several decades ago, and the most powerful nuclear weapons today would be able to destroy or damage large cities, even at the most. And yes, there are thousands of nuclear weapons.
But due to the decreased potency of even the strongest nuclear weapons, and there still being a very finite number, even the capitalists probably understand that an irradiated world would be a terrible place to lord over, even if you survive.
Nuclear weapons would most likely and would best be used to damage, delay and destroy military and industrial centers, and with how interconnected the world is now because of the internet, gps, cell phones, and supply chains, a country would be way less likely to get involved in combat when it's industrial bases, bourgeois palaces and military-intelligence strongholds are utterly demolished, out of basic resources and power and labor, things would resolve relatively quickly, pacifying countries out of a fight with relatively few deaths, since there is no point in launching weapons at massive populations centers if it can be helped, since it would just invite more war, death, destruction, disease, sadness, vengeance, danger.
I can't speak for the Global North, but I find it hard to believe that those launching nuclear weapons would just shoot them everywhere all over the place at civilians, that would be ridiculously stupid, even in an extreme scenario, all but signing the death warrant of the human species, and targeting civilian and food storehouses and infrastructure would be worse than pointless, it would be stupid.
I think/hope/imagine that if or when NATO is stupid enough to use nuclear weapons, that China, Russia, Iran, Palestine and the DPRK would already be 20 steps ahead, they have been planning for this for decades.
China and Russia's advanced and partially automated and augmented defense systems would scramble, hack into, shut down, disable, redirect, or outright destroy or prevent nuclear missile launches. Drones would hack into and shut down facilities or weapons themselves. Infrastructure could be shielded and damage minimized in various ways, and supply chains are something that Global South understands intuitively more than the Global North.
I hope it never comes to it, but I think a potential World War 3 would be mostly conventional warfare, and even if it isn't, a nuclear war wouldn't mean the death of all or even most of humanity (hopefully) and things would resolve in the Global South's and socialism's favor no matter what.
I'm far less optimistic myself. If NATO goes in then the conflict will become existential for the west. However, the reality is that the west is simply not capable of conducting this sort of war because it lacks the industry to do so. Look at what happened with Ukraine, every red line was eventually broken. The west sent all the weapons it said it wouldn't send, and now that Russia is still winning, the talk is turning to sending in troops.
Nuclear weapons will likely be used in a tactical way first, both Russia and US have lots of tactical nukes. This can easily escalate into use of strategic nukes though. It doesn't even have to happen intentionally. One side might simply miscalculate or misread the situation and launch their strategic nukes at the other. You can't make the assumption that people in charge are rational because if they were we wouldn't be where we are in the first place.
And regarding shooting nukes at civilians, that will absolutely be the case. Do recall, that the only time nukes were used they were used against civilians. There is also a deeply cynical angle to it, that the big powers would likely nuke developing countries simply to ensure they don't come out unscathed.
I don't assume that people are always or automatically perfectly rational, and of course timing and emotions and short-term thinking play a huge role as well, and yes, the U.S. using nuclear weapons against Japan was a horrific war crime and wasn't even necessary or justified, on any level.
What I am saying is that, when the chips are down, I highly doubt that the capitalists/imperialists/NATO/the Global North/military operators are going to be like:
Guy 1: "Okay, we sent out dozens of nukes at Beijing and Moscow, and things still aren't in our favor. Let's start targeting farms in China, and populated cities and farms and the dams in China next, then Moscow."
Guy 2: "Dude, China has fighters, sensors, drones, heat-seeking missiles and deflectors and all kinds of shit surrounding the Three Gorges Dam, and Shanghai and Shenzhen. This is just inviting more and more violence."
Guy 1: "That's CCP propaganda"
Guy 2: "It's fucking not! We can't possibly sustain more launches, and China and Russia are preparing to launch theirs, actually, scratch that, we're 10 minutes from being destroyed. We have to hope that troops in Ukraine can hold off Russia from-"
Guy 3: "We've gotten orders to suspend missile launches, we gotta move the brass to a different location"
I don't think that's how it would play out. What I think is more likely is that one side decides to risk a decapitation nuclear strike where they try to overwhelm the other and launch a massive strike, the other side retaliates with their own. We get a nuclear winter and most of us starve to death.
Nuclear winter could actually be a bonus considering the changing climate, so with possible diminushing trade to the imperialist core, specially if they nuke the periphery on their attempt to cling to power, the Global South might only have a bad, but not horrible year, before things improve for the average person.
Perhaps my info on this was a little old, and seeing as my country might be one of the few to not have mass starvation in such a scenario, according to one of the studies I saw, I might have also been too optimistic about other countries' chances.
It seems nuclear winter could lead to an 8 degree maximum drop in temperature with a 4 degree drop after a decade and lasting a while. Perhaps. So, much worse than climate change at the current time.
Although I do still wonder about how close to reality the soot modeling is due to possible new materials and differences from countries, which might make a big difference on the actual result, either for better or worse.
Yeah, nuclear winter is going to be much worse than the global warming. The soot modelling is based on what we see happening after volcanic eruptions, so it's not going to be that far off. However, the fact that we don't know just how bad it gets underscores the risk for all humanity here. We are talking about billions of people dying as a result.