Philip Jenkins’s contribution to The Globalization of Christianity (edited by Gordon Heath and Steven Studebaker) offers sobering and exciting news by turns.
On the sobering side, he describes the statistical stagnation of Christianity, and compares it to the spread of Islam. For the past century, Christianity has held steady at 1/3 of the human population. It’s grown, of course, but it has not grown as a proportion of the world’s population.
Islam has. “In 1900, the 200 to 220 million Muslims then living comprised some 12 or 13 percent of humanity, compared to 22.5 percent today, and a projected figure of 27.3 percent by 2050. Put another way, Christians in 1900 outnumbered Muslims by 2.8 to 1. Today that figure is 1.3 to 1, and by 2050 it should be 1.3 to 1. Put another way, there are four times as many Christians alive as there were in 1900; but over the same period, Muslims have grown at least seven-fold” (21).