Interestingly, scientists have actually tried predicting how nuclear war would affect the climate. Because why not?
Smoke from devastating wildfires would blot out the sun’s rays and reduce global temperatures for awhile, sort of like a massive volcano eruption. Of course that would also impact agriculture in a major way and lead to widespread famine, in addition to wrecking the ozone layer, making cancer rates skyrocket along with the radiation fallout and we’re not even talking the millions or billions who’d be incinerated immediately.
overall, bad, very bad
https://www.sciencedaily.com/releases/2021/10/211013174023.htm