It's tough to know exactly, but it's doesn't cause much change in sunlight and temperature to cause mass crop failures. There are some US government estimates that the fine particulates from even a "limited" nuclear war would cause such an extensive collapse in agricultural output that you might see something like 90% of the human population starve just in the first year. Even if though that might not be a literally exctinction level event, it would be such an epochal society-altering event that there's no sense in which a country would come out the other side as a "winner" even if they were completely untouched by the actual nuclear blasts or fallout.

The redditors who are enjoying this little visual are watching themselves and everyone they know and love starving to death in the aftermath.