Not sure you know what a nuke is, but if one were to be set off in Houston alone; it would kill half of Texas. I don't know much about this topic but I'm pretty sure the two strongest countries going at it will lead to utter destruction and a holocaust worse than WW2.
As said by scientists it takes approximately two simultaneously impacted nukes to change the world's climate. I think that everyone on Earth would eventually die after the war. This is not to be narcissistic but you have to admit if America and China used their nuclear weapons against each other everyone else would be severely effected.
During the Cold War, both the USSR, and the US had their fingers on the big red button, but due to Mutually Assured Destruction, we are still here today. China has a supply of ~300 nuclear devices, and the US has ~7,700 (1), which means that both countries could do more than enough damage to wipe each other out, and with both countries always nearly tied for the #1 spot economically, it would be world murder/suicide for such a thing to happen.
For a long period, the doctrine of Mutually Assured Destruction was used, the idea that an overwhelming annihilation would make use of nuclear weapons impossible as a matter of policy. It worked so well that even when it was replaced, it remained popular in the public mind. What replaced it is the idea of proportional response. If another state used a nuclear weapon, the US would retaliate with one of the same tonnage on a similar target. While a few nuclear weapons would cause a catastrophic loss of human life, it wouldn't turn our world into some post-apocalyptic wasteland. Further, China has about 200 devices, and only about sixty missiles capable of reaching US targets. Additionally, China's nuclear policy is Minimal-Deterrent, meaning their arsenal is supposed to be just big enough to make attacking them seem unduly dangerous without possessing any first strike capability.
So from a doctrinal standpoint, there's no looming nuclear holocaust. Sorry.
Maybe, but China has far less nuclear weapons then the United states. I think the world would survive the war, even if the radiation made life difficult. Fortunately, I do not think a way between any superpowers is going to happen. We are to financially tied. Plus, I don't think anyone wants to test Mutually Assured Destruction.