How long until we believe? Until we care?

Must the world flood? Melt? Self-destruct? What will it take to make us think "Hey, yeah, maybe there is something to that whole climate change mumbo jumbo after all"? Must the earth decline into a barren, scorched wasteland resembling Hollywood's vision of the apocalypse? Must aliens arrive, take one look around and say "damn, man, this shit is fucked up" and immediately leave before we realize that damn, man, this shit is fucked up? Must sea creatures take over the world via the ocean (there's only one, since it covers every inch of the earth, now) and put all the land animals in tanks and have us perform tricks at LandWorld (tm) before we think to do anything about it?

@DavidMark