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

Enough to make an explosion so bad, the ash would block the sun from entering basically forcing a winter like Mt Tambora did to a smaller extent (but still causing the Year Without a Summer)