... if the low-lying islands of the world are swallowed by rising oceans?
Maybe you think it won't happen, but what if it does? Can you picture the relocation that will be needed? Or do you picture storms or waves suddenly devouring whole populations before any full-scale relocation effort takes place? What does the island in your mental picture look like? Does it look like Manhattan?
ADDED: Why is this on my mind? I've been reading "The Sex Lives of Cannibals: Adrift in the Equatorial Pacific."