Grist: How will the world end? A giant meteor? Zombie apocalypse? Death Star target practice!? One scientist thinks our planets death knell is going to be climate change, on an epic, terrifying scale but, fortunately, not the kind we need to worry about. The runaway greenhouse which is thought to have happened on Venus in the past is basically a climate change worst-case scenario: We reach a critical point where the atmosphere is so thick with greenhouse gases that no sunlight can escape back...