Peter Illyn looks more like a hard-living, grizzly-fighting mountain man than a leader of the movement that’s birthing pious young reformers like Vekasi-Phillips. A bearlike 6’1” and 280 pounds, Illyn sports a snakeskin eye patch that hides what he lost in 2002 to ocular cancer—and hikes with a trekking pole to offset depth-perception issues. The 52-year-old’s face is large and expressive, but weatherworn and flecked with the pockmarks left by a childhood bout with spinal meningitis. Months after meeting him in Charleston, West Virginia, I decide that he most resembles an itinerant preacher who’s ridden the frontier so long he now wears the miles in his facial creases and stiff-legged walk.

Since 1989, when Illyn experienced a conversion in the wilderness that inspired him to start preaching the green gospel, the La Center, Washington, pastor has spent untold hours converting young evangelicals to creation care. In its simplest definition, creation care is a movement in which a growing number of Christians believe that they are directed by God and mandated by the Bible to be stewards of the Earth and its creatures. (Genesis 2:15 is a favorite passage: “The Lord God took the man and put him in the Garden of Eden to dress it and keep it.”) They’ve chosen “creation care” over “environmentalism” to emphasize that they’re talking about something divine, not just the planet’s physical carpet of lakes and trees—and to separate themselves from liberals whose abortion and gay marriage politics they don’t share.

As a group, their numbers are growing: In a 2008 Barna poll, 90 percent of evangelicals said they would like all Christians to take a more active role in caring for the planet, while a 2009 poll taken by Public Religion found that 64 percent of white evangelicals believe in global warming. In those polls, it’s the “younger, more moderate evangelicals who are experiencing the greatest shift when it comes to the environment...