>>507963330There wouldn't be enough fallout to cause a nuclear winter. Modern thermonuclear weapons rely on hydrogen fusion as the main explosive force which doesn't create radioactive isotopes (just fuses hydrogen into helium). The uranium or plutonium components produce fallout but because they're just used to trigger the fusion there's much less fallout than in conventional nuclear weapons.
Plus there's been over 2000 test detonations of nuclear weapons with no wider ecological effects, so the idea of a nuclear winter is absurd. Really only way a nuclear winter would be feasible would be upper atmosphere detonations of tens of thousands of cobalt salted nuclear weapons which nobody developed.