It woud be good to ask the opposition what they propose in place of Earth Hour. At the same time, it may be good to give some bad/silly examples of alternatives people have actually proposed. One silly example is "energy roulette week" (a complex game to educate about 'real' energy consumption. This is delusional because of its complexity.
Another silly example is "human achievement hour". "To celebrate Human Achievement Hour, participants need only to spend the hour from 8:30 pm to 9:30 pm on March 23 enjoying the benefits of capitalism and human innovation: Gather with friends in the warmth of a heated home, watch television, take a hot shower, drink a beer, call a loved one on the phone, or listen to music."
In other words, do what you usually do (?!?) This is ineffective because it's way too too vague.