This is a highly technical document showing the Worldwide Effects of Nuclear War. It shows what would happen if multiple warheads were detonated on multiple continents.
However, as the majority of our knowledge on nuclear war comes from a single instance and lots of theory this document is based upon good science, but it is still only a hypothesis.
That is not to say it is inaccurate, If I understand gravity and the effects of trauma on the human body I can come up with a very good hypothesis of what would happen if a person jumped off a building without ever having seen it happen.
Now as a prepper, nuclear war isn’t something that keeps me up at night, but a rogue nation or terror group detonating a small device in a city is within the realm of possibility. Additionally I live in a state with more than one reactor so I do have some level of preparation for a radiological event.
As with all things, my philosophy is simple, if something scares you prepare for it the best you can and then move on with your life.
link below opens a PDF from the 1975 US Arms Control and Disarmament Agency on the Worldwide Effects of Nuclear WarWorldwide Effects of Nuclear War