Does turning off lights globally during "Earth Hour" reduce global warming, and what is the ruling on participating in this act?

The permissibility of participating in what is known as "Earth Hour" needs to be verified by specialists. As for the Sharia ruling, the basic principle is permissibility, because it falls under customs, and the basic principle concerning customs is permissibility unless there is evidence of prohibition. There is nothing here that prohibits it, due to Ibn Taymiyyah's statement: "The basic principle concerning customs is clemency (permissibility); nothing is forbidden except what Allah has forbidden."