There were just over half that many when I was born, and in four decades time there could easily be more than nine billion.
Even if one is skeptical about human-generated climate change, peak oil or environmental degradation, just the amazing heft of that many people demanding the current level of resources seems an improbable effort with that many more people. And shouldn't the poorest and most vulnerable reasonably demand easier and more reliable access to food and water? energy and communication? housing and just government? education and health care? And just plain old peace?
Orienting resources and talent to this problem seem like key questions -- and questions that persons of faith should take seriously. An aesthetic or esoteric faith fails morally when it treats the welfare of billions as an added optional extra.