The United Nations projects that global population, about 7.4 billion today, will reach 11.2 billion in 2100 (with Africa accounting for the lion's share of growth). For anyone concerned about climate change, this is a sobering prospect. The world already struggles to limit carbon dioxide emissions, so what are the prospects for climate mitigation in a world with 50 percent more people? But proposals to slow population growth can encounter stiff resistance. The real problem, some argue, is that energy consumption will grow much faster than population as the world gets richer—and in any event, past initiatives to limit population growth have sometimes taken sinister forms. Below, experts from Nigeria, the United States, and China debate these questions: Are efforts to limit population growth a legitimate element of climate mitigation—and can they be pursued without exacting unacceptable ethical costs?