[wobbegongz]

We have tested that also. During 1945 we burned down 69 cites and killed 800 000 in Japan. The two small nukes was only 5% of the smoke.

The result was at most an cooling of the global temperature of 0.1-0.2 Celsius. But the "multiple uncertainties mean we cannot say for sure".

https://www.carbonbrief.org/guest-post-did-bombing-during-se...

So we need about 5-10 times larger bombings when ww2 to cool the global temperature with one degree. But we have increased the global temperature with one degree thanks to global warming. So you need at least 10-20 times larger bombings then ww2 to get a tiny atomic winter. And probably a lot larger to get any catastrophic cooling.