@CWO:
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The theory behind a nuclear winter (as I understand it) is that a global nuclear war would pump vast quantities of smoke and fine particulate matter into the upper atmosphere, where it would reflect away enough sunlight to lower the planet’s temperature and disrupt the ecosystem. This is essentially what killed the dinosaurs 65 million years ago, when an asteroid hit the Earth and vaporized a large piece of the planet’s crust. Climate change on this scale doesn’t happen overnight. A global nuclear exchange, by contrast, is something that can happen within a matter of hours.
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You understood it right and gave a good summary of this event.