One of the questions this season has been “What is In the Shadow of The Statue?”. I think it’s pretty clear that the thing they’re talking about is the H-Bomb, Jughead. I also think that’s what caused “The Incident”. That H-Bomb is going to go off.
That would explain two other long standing questions: What’s that medicine that Desmond was taking while he was in the hatch, and why were they wearing those yellow suits? That medicine is to prevent radiation sickness, and the yellow suits are to protect them from radiation fall-out.