The equation seems fairly simple: The more the world's population rises, the greater the strain on dwindling resources and the greater the impact on the environment. The solution? Well, that's a little trickier to talk about. Public-health discussions will regularly include mentions of voluntary family planning as a way to reduce unwanted pregnancies and births. But, said Jason Bremner of the Population Reference Bureau, those policies can also pay dividends for the environment. "And yet the climate-change benefits of family planning have been largely absent from any climate-change or family-planning policy discussions," he said. A 2010 study published in the...