In Rod Serling’s Twilight Zone episode “Midnight Sun” posed the conundrum (a riddle with a pun as the answer) whether the world would end in global warming or cooling. Robert Frost also pondered this riddle in his 1920 poem.

I think I have the answer: “Fire!”

The pun is that this is what you say to clear a crowded movie theater. Now that you have the punchline, you can get the setup in my column in The Space Review which is up.