Researchers who study obesity can calculate calories, measure weight and, over time, convincingly link the two. That straightforward equation supports a sim­ple argument for altering the built environ­ment to get children moving. But could a less clinical connection with nature be equally important? Across the nation, researchers, environmentalists and political leaders are sounding the alarm over a nonmedical condition dubbed “nature-deficit disorder.”

In a popular 2006 book, Last Child in the Woods, journalist Richard Louv coined the term, which he defined as a critical disconnect between children and nature. The book lamented this fundamental loss—and its social, psychological and even political implications. As kids spend fewer hours exploring, playing or just poking around outdoors, Louv argued, they lose creativity, a sense of belonging and an appreciation for the world around them.

Nature’s broad health value has not been rigorously studied, partly because it is difficult to evaluate clinically, notes Richard Jackson, an adjunct professor of environmental health at the University of California, Berkeley, and former director of the National Center for Environmental Health at the Centers for Disease Control and Prevention. But, he argues, that snag shouldn’t slow efforts to address the situation. “The tragedy is that we removed nature from children’s lives without the benefit of a randomized, controlled clinical trial, so why would we need trials to restore childhood?” Jackson says.

Indeed, governmental organizations are already spring­ing into action. Connecticut Governor M. Jodi Rell, for instance, recently launched “No Child Left Inside,” an initiative to inspire families in his state to explore the outdoors. The Texas Parks and Wildlife Department has rolled out “Life’s Better Outside,” a similar public awareness campaign. —K.B.