"We are the renters of this world, not its masters," reminds Pooshkar, a precocious 13-year-old member of a youth environmental defense group in India. He and his fellow voraciously energetic students actively rally against the use of plastics. In Africa, a renaissance man teaches citizens to harness solar power to cook food. In Papua New Guinea, villagers practice sustainable logging to save their rainforests. A woman in London uses her PR savvy to start a successful environmental communication...