You may not know it yet, but nature is an abundant source of happiness. New research shows that even if you’re trapped in an office or only able to step outside for a moment, small exposures to outdoorsy indicators—seeing trees, the sky, or hearing a birdsong—can boost your mood. And the best thing is, the effect of being in nature doesn’t disappear once you’ve returned to a cloistered cubicle or apartment: It can last for several hours, with especially strong results for people who suffer from mental disorders.