Nuclear winter was Soviet propaganda developed to counter our Star Wars propaganda, as the Russians knew they couldn’t keep up with us technologically.
So, you found a video on the Internet. How cute.
The video is from 1984, when the “nuclear winter” scenario was being propagandized. Later science proved that Carl Sagan was a lying bastard, and fudged the calculations as an additional propaganda point against any nation possessing nuclear weapons. IOW, it is bullshit.