The concept of "nuclear winter" is a great example of science gone wrong. As it turns out, the original 1980s report vastly overestimated the amount of combustible fuel in cities and inaccurately estimated both modern nuclear weapon yield and blast size. Nuclear war would not create firestorms capable of injecting soot into the stratosphere and would not cause years-long crop failures. Nuclear war is, in fact, quite survivable.
https://skeptoid.com/episodes/4244
https://www.nature.com/articles/475037b
https://www.quora.com/How-many-nukes-would-it-take-to-cause-...