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The definition of ‘evangelical’ is hard to pin down, and even harder to measure. Generally, when people say ‘evangelical’ they mean ‘true believers.’ When the World Christian Database measures ‘evangelical,’ they are referring to members of historically Evangelical denominations, which can be something entirely different. While I think measuring ‘evangelical’ is a very challenging process—and not one I would undertake, myself—Operation World’s measure is probably the closest to the commonly understood meaning of the term.

In the 2010 edition of Operation World, evangelicals were estimated at 545.8 million, or 7.9% of the world, and growing at 2.6% per annum. These were broken out into 7 regions: North America, 94 million; Latin America, 135 million; Europe, 18 million; Africa, 182 million; Asia, 146 million; Pacific, 6 million; and Caribbean, 6 million.

For each of these regions, OW further gives annual growth rates as of 2010. The challenge with projecting growth rates into the future: they will certainly not remain the same, and trying to predict precisely what they will be is a bit of a fool's errand. Many things will impact them, but the biggest: the larger the population, the more it will be similar to the population of the region as a whole, and the more it will take on the regional population characteristics. In the largest populations, births born to Christian homes grow the church far more than conversions do (globally, about 10 times as much). Conversions simply determine 'by how much' a subset 'beats' the overall population rate: but if the population growth rate fluctuates up and down, we can expect the church growth rate to do the same.

To try to estimate when evangelicals will be “half the planet” (or 50% of the population), I have broken them out by region, and then estimated evangelical populations for the years 2025, 2050, 2075 and 2100. The methodology for this is as follows. We start with the evangelical population and annual growth rate for each region as given by Operation World. We project 2025 from 2010 based on this. Then, we vary the evangelical annual growth rate for 2050, 2075 and 2100 based on the changes in the region’s population growth rate over that time.

As an example, Africa has an evangelical AGR of 3.6% and a population AGR of 2.5% in 2010. In 2025, the population AGR has dropped to 2.4%, so (using a ratio) we drop the evangelical AGR to 3.5%. This is obviously a fairly rough process, but it does reflect the enormous role that demographics plays in growth. The analysis of this result of the methodology is as follows.

Africa. From 182 million in 2010, evangelicals grow to 3 billion, or 69% of Africa by 2100. This is powered by sustained but declining population growth, falling to 1.95% per year by 2100. I suspect the model significantly overstates the growth, but I have not modified the methodology here. In spite of the specific numbers, I am very comfortable with a projection of Africa’s having crossed the 50% threshold somewhere between 2075 and 2100.

Asia. From 146 million in 2010, evangelicals grow to 1.2 billion, or 24% of Asia’s 4.3 billion by 2100. Evangelicals are, in this model, predicted to slip from 3% per annum growth today to 1.5% per annum in 2100, due to the projected fall in population growth. This, too, seems a fairly realistic projection. While there are significant gains in the number of evangelicals in China, growth in other places in Asia is presently fairly flat.

Europe. From 18 million today, this model projects growth to 26 million evangelicals by 2100. The annual growth rate will decline along with the falling population AGR, which is projected to hit its peak ‘low’ rate of -0.246% per annum around 2075. Since the evangelical AGR will not be as slow as the population’s, Europe will actually become more evangelical (by percentage of the population): rising from 2.5% in 2010 to 4% in 2100 in this model.

Latin America. From 91 million evangelicals today, evangelicals would rise to 477 million by 2100, or 70% of the population. As with Africa, the precise numbers are likely overstated, but it still seems likely Latin America would be ‘over the 50%’ threshold.

Caribbean. From 6 million in 2010, evangelicals would rise to 31 million, or 77% of the population. They would have crossed the 50% threshold in 2075. While the model probably overstates the number, it appears that crossing the 60% threshold is possible.

Pacific. From 6 million, evangelicals would rise to 21 million, or 29% of the population. While comparable in starting population size with the Caribbean, the much smaller growth illustrates the power of a much smaller annual growth rate.

I confess this methodology is very imprecise, and should certainly not be relied on for anything other than an attempt at estimating which regions will be 'across the line.' Any number of things--warfare, pandemic disease, revival, persecution, and so on--could significantly interrupt this. However, I think it's a fairly realistic model because it depends in large part on demography, and demography is fairly consistent over the long run of decades and centuries.

The net result of this model is this projection: in 2100, the world would have 4.9 billion evangelicals out of an 11 billion population, or 44.2%. Because Africa and Latin America projections are probably too high, it seems almost certain 4.9 billion is likely too high as well; this means the world will likewise almost certainly not be over 50% evangelical by 2100. Further, as evangelical populations get larger, their population growth rates will almost certainly slow. This means crossing the ‘50% line’ is likely far further off than 2100.

If one wished to change the date, how might we set about it? The only way to do so would be to make a significant difference within a large population: increasing the Pacific’s % evangelical, while worthwhile, wouldn’t make much of a dent in the global average. The most high-impact population to influence the global total would be Africa and Asia’s. Africa is, by and large, becoming rapidly evangelical. Asia, on the other hand, is a strong mix of reached and unreached areas. More effort there could shift the ‘clock’ significantly: but this is easier typed on a page than done in the field.