"Studies dating back at least three decades clearly show the power of social norms. We tend to ascribe our actions to more high-minded motives, or to practical concerns about money. But at its core, our behavior often boils down to that old mantra: Monkey see, monkey do. Researchers are now learning how to harness that instinct to nudge us to go green. ... Psychologists and behavioral economists are increasingly concluding that for the masses, a simpler, cheaper approach may be in order. It can include new laws and taxes, as in D.C., but it doesn't have to. The magic ingredient: Peer pressure."