It ' s really questionable in what conditions could 100 nukes actually cause nuclear winter . In fact it ' s really unlikely . Note that it ' s not the nukes themselves that cause the nuclear winter effect . It has nothing to do with the explosions , or the potential fallout and how muchif any fallout is generated depends on how you use those nukes , not just yield . Nuclear winter would be caused by lots of very fine particulates being created by fires over a very large area . That is , you need to start a lot of fires , need a lot of burnable material and need the conditions for that fire to spread and sustain itself . Outside of nuking very dry heavily forested areas for no good reason , there aren ' t many ways of actually causing this , even if you ' re deliberately trying to .