From an Interview with Philip Jenkins (author of The Next Christendom: the coming of global Christianity.)
Interviewer: What's the big picture? What will the mass of Christians look like 50 years from now?
Jenkins: "My argument is that one of the big factors will be ethnic. In the United States, looking at the whole population, something like a third of Americans will have either Latino or Asian roots, and the vast majority of those come from backgrounds, which are presently Christian. I think it's quite likely that those people will still continue to be Christian and they will certainly be very dominant voices in the Catholic Church and probably most of the mainstream churches.
Globally, Christianity will be much more of a black and brown religion. The figures I suggest, with all awareness of the queries about numbers, somewhere between four fifths, and five sixths will be in Africa, Asia, Latin America, or from migrant communities in the West. Non-Latino white Christians will represent only about a fifth or sixth of the whole, so Christianity will be much more a black and brown religion."