This interesting statistic is somewhat mind-blowing. In James D.G. Dunn’s 1970 essay “Spirit-Baptism and Pentecostalism” he writes, “Pentecostalism is now reckoned to be between ten and fifteen million strong, and is still growing faster than any other Church.” *
According to BBC’s 2009 report, “During the last three decades of the twentieth century Pentecostalism grew very strongly and there are now over 250 million Pentecostals around the world, who make up more than 10% of all Christians. (Some writers suggest the number is more like 500 million.)”
The global population sits at about 7 billion now. In 1970 it was around 3.7 billion. The world population has almost doubled in the last four decades. Global Pentecostalism has grown somewhere between seventeen times (if 15 million to 250 million) to fifty times (if ten million to five hundred million) larger in the last four decades.
I presume some of these statistics will be debatable, especially as regards whether “Pentecostal” is the correct label for many charismatic Christian movements that wouldn’t necessarily espouse traditional Pentecostal dogma. Also, I don’t know how to go about validating Dunn’s estimate in 1970 or even modern estimates. That said, even if the statistic needs to be tweaked here and there, that’s impressive growth.
Also of interest: T.M. Luhrman, Why We Speak in Tongues (NYT)
* see James D.G. Dunn, The Christ and the Spirit: v. 2: Pneumatology (Grand Rapids: Eerdmans, 1998), 86.