system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If USA and Russa had an all-out nuclear war during the Cold War, would there really be a nuclear apocalypse like we see in movies?
gpt
To be honest, no one really knows.

We know there are enough nuclear weapons to take out the worlds major cities, but if countries like India, Brazil and South Africa weren't directly involved, they might survive with their populations intact  They could emerge relatively unscathed at the worlds new superpowers, and humanity would not take too far of a step backwards in terms of development.

We speculate that the smoke from the ensuing fires would result in reduce sunlight reaching the earth.  That could result in anything from a few lean years to a complete agricultural collapse sending man kind back to the Dark Ages, or worth.

There would also be nuclear fallout, and this could be made much worse if dirty bombs were involved.  This could be the difference between land being resettled in a decade, or being uninhabitable for centuries.  It would also impact how much poison enters into the overall ecosystem impacting all humans.