The world's leading authority on the quantitative future of religion shares how one can make projections of religious affliation. A statistical projection of religion is made for the year 2025. Then three alternative scenarios for world religions are offered for the year 2200.
The opportunity to project the future of religious affiliation has presented itself for the first time with the recent availability of four publications and two databases. Foundational demographic data for every country in the world are available for the years 1950-2025 through the United Nations Demographic Database (see United Nations, 1994). Data on religions and Christianity for every country are available through the World Evangelization Database (see World Christian Encyclopedia  and Our Globe and How to Reach It ). Data beyond 2025 for the world's nine major continental areas are available for the first time in the UN's publication Long-Range World Population Projections: Two Centuries of Population Growth, 1950-2150 (1992).
The intersection of these data form the starting point for a quantitative analysis of the future of religion. The demographic projections of the United Nations provide a foundation on which religious data can be compared. This can be described as a five-stage process.
Stage One: demographic analysis by country
Christian data are more complete globally than data on other religions. A detailed analysis can be performed by matching data on Christianity with the population projections for every country of the world. If none of the 1990 percentages are adjusted but assumed to remain static, the demographic effects on Christian affiliation can be analyzed on both regional and global levels. This reveals the differential growth of adherents to Christianity depending on population growth where they live. This is the first stage of demographic analysis by country.
Stage Two: religious analysis of Christianity
A more realistic application is to use current trends to make adjustments to the Christian data. Thus, if evidence exists that the Christian church is in decline in a particular country, then the percentage to be matched to that country at a future date will be lowered to an appropriate level. With adjustments made to Christian populations in each country a second stage of analysis is added. Now one can view the effects of not only demographic change but change in religious adherence.
But these first two stages of analysis have two important limitations. First, they only analyze the Christian situation. Without reference to other religions and nonreligious, it is easy to miss the overall context of religious change either by country, region, or globally. Second, they only take us to the year 2025. Our next stages will, therefore, have to overcome both of these limitations.
Stage Three: multi-religious and regional futures projections
The most detailed table of religions by United Nations regions is published yearly by Encyclopaedia Britannica in its Britannica Book of the Year. This table includes all religions by major region and is thus suited perfectly for demographic manipulation.
It overcomes the first limitation of the first two stages -- all major religions are included. The second limitation is overcome in that regional projections have been published by the United Nations for the years 2025-2200.
Analysis of the Britannica tables begins by using the 1990 table as a base from which to project all future tables (to 2200) using only demographic tools. Thus, the regional totals reflect United Nations projections while all religious percentages within a region remain unchanged. This allows us to examine how demographic growth or decline alone within a particular region affects the global total. This yields remarkable insights into what we can expect from the most consistent source of growth and decline of religious and nonreligious adherence -- births and deaths. This amounts to our third stage of analysis of the future of religion (seen in Table 2, column 1)
Stage Four: Multi-religious and country-by-country future projections
The fourth stage allows us to use results from our country-by-country analysis to update the Britannica tables to 2025. From this base, more reasonable demographic future projections can be made. In addition, for the first time we can see our Christian projections in the context of the world's religions and nonreligions. (seen in entire Table 1).
Stage Five: alternative scenarios for the year 2200
The fifth stage of analysis completes our methodology by making adjustments to the end of our study period, A.D. 2200, based on conservative assumptions about religious change. The adjustments yield what could be considered our "most likely" scenario.
The results of these projections of religious statistics are presented in two tables below. Table 1 is entitled "Adherents of World Religions, 1900-2025." Table 2 is entitled "Scenarios for the Year 2200: Adherents of World Religions."
Table 2, "Scenarios for the Year 2200: Adherents of World Religions," inserted below, offers three baseline projections for 2200. The first two columns offer population projections based on UN demographics from 1990 or 2025, respectively. The third column offers a "Most Likely" scenario for the year 2200, factoring in assumptions on possible growth through change of religious affliations.
In summary, it shows Christianity increasing from 33.2 percent in 1990 to 37.9 percent by 2200, while Islam also increases from 17.7 percent in 1990 to 22.6 percent by 2200. Nonreligious persons and atheists, on the other hand, grew rapidly over the period 1900-1990, then decrease from a combined percentage of 20.5 percent in 1990 to 16.1 percent by A.D. 2000.
These results could be revised simply by modifying either the assumptions or the actual figures used to calculate religious change. For illustrative purposes, two additional scenarios for 2200 have been added to Table 2.
Scenario Two: Muslim Revival
First, a plausible future is one in which Islam makes unprecedented inroads into the Western world. (See column labeled "Muslim revival"). The assumption is made that 1 percent of the Christians in Europe, North America, and Oceania defect to Islam every twenty-five years. In this senario Christians lose 0.9 percent of the world's population (dropping from 37.9 to 37.0 percent while Muslims gain from 22.6 to 23.5 percent) over the 175-year period 2025-2200.
Scenario Three: Nonreligious growth
A second alternative scenario is constructed by an assumption that Muslims in Asia are hard hit by secularization, losing 0.5 percent every twenty-five years from 2025 to 2200. The result, presented under "Nonreligious growth" in Table 2, is that Muslims lose 1.2 percent of the world's population over the 175-year period.
A secondary effect of this study is the evidence it provides for the quantitative resiliency of religion over the next two hundred years. Purely demographic changes do not show a massive decline in religious adherence. The onus would be on the person putting forth such a statement to prove that massive defections from religious adherence represent a plausible assumption.
BARRETT, DAVID B. World Christian Encyclopedia: a Comparative Survey of Churches and Religions in the Modern World, AD 1900-2000. New York: Oxford University Press, 1982.
_____. "World Religious Statistics" (annual compilation). In Britannica Book of the Year. Chicago: Encyclopaedia Britannica, 1994.
BARRETT, DAVID B., and JOHNSON, TODD M. Our Globe and How to Reach It: Seeing the World Evangelized by AD 2000 and Beyond. Birmingham, AL: New Hope, 1990.
United Nations. Long-Range World Population Projections: Two Centuries of Population Growth, 1950-2150. New York: United Nations, 1992.
______. World Population Prospects 1992. New York: United Nations, 1994.
Copyright 1995 by Todd Johnson. This article first appeared in The Encyclopedia of the Future, edited by Graham T.T. Molitor, Macmillan, 1995.
EDITORS NOTE: To scholars, recently this article has been updated, with different scenarios and long-range demographics significantly different from those cited above. For more, see Johnson, T. M., & Barrett, D. B. (2004, November). Quantifying alternate futures of religion and religions. Futures, 36(9), 947-960.
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