What do people mean when they say we have enough nukes to destroy the world?

Question

Are they just talking about erasing cities/mankind from the surface or the combined energy from them all is enough to significantly disfigure the surface? Or would it be the aftereffects of the bombs that cause the destruction?

In: 1

Answer 1

And they think it would cause a nuclear winter. Which would put enough dirt/dust/debris/ash into the air so that no food would grow, so could end most life on the planet.