>>938916543
Of the ~2,400 nuclear weapons detonated during the Cold War, only 527 of those were not underground. Of those, they were detonated over a 20-ish year period (most between 1945 and 1962, but the French and Chinese conducted several more atmospheric tests after that), in fairly remote locations (deserts, ocean islands, the tundra, etc. — exact locations depends on the country who was detonating them).
The nuclear winter hypothesis states that the smoke from the firestorms caused by massive numbers of near-simultaneous detonations of nuclear weapons will enter the upper atmosphere and reflect sunlight. You need two things for that which are not satisfied by the nuclear testing history: 1. they need to actually burn a lot of things (very little burning happens in the desert — you need to set cities, forests, plains, etc. on fire) because you need a lot of smoke (more than just the mushroom clouds), and 2. you need them to happen basically at the same time (e.g. the same few days), not spread out in time like nuclear testing was.
