Why Muslims Are Rising Fastest and the Unaffiliated Are Shrinking as a Share of the World’s Population

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The religious profile of the world is rapidly changing, driven primarily by differences in fertility rates and the size of youth populations among the world’s major religions, as well as by people switching faiths. Over the next four decades, Christians will remain the largest religious group, but Islam will grow faster than any other major religion. If current trends continue, by 2050 …

* The number of Muslims will nearly equal the number of Christians around the world.

* Atheists, agnostics and other people who do not affiliate with any religion – though increasing in countries such as the United States and France – will make up a declining share of the world’s total population.

* The global Buddhist population will be about the same size it was in 2010, while the Hindu and Jewish populations will be larger than they are today.

* In Europe, Muslims will make up 10% of the overall population.

* India will retain a Hindu majority but also will have the largest Muslim population of any country in the world, surpassing Indonesia.

* In the United States, Christians will decline from more than three-quarters of the population in 2010 to two-thirds in 2050, and Judaism will no longer be the largest non-Christian religion. Muslims will be more numerous in the U.S. than people who identify as Jewish on the basis of religion.

* Four out of every 10 Christians in the world will live in sub-Saharan Africa.

These are among the global religious trends highlighted in new demographic projections by the Pew Research Center. The projections take into account the current size and geographic distribution of the world’s major religions, age differences, fertility and mortality rates, international migration and patterns in conversion.

As of 2010, Christianity was by far the world’s largest religion, with an estimated 2.2 billion adherents, nearly a third (31%) of all 6.9 billion people on Earth. Islam was second, with 1.6 billion adherents, or 23% of the global population.

If current demographic trends continue, however, Islam will nearly catch up by the middle of the 21st century. Between 2010 and 2050, the world’s total population is expected to rise to 9.3 billion, a 35% increase.1 Over that same period, Muslims – a comparatively youthful population with high fertility rates – are projected to increase by 73%. The number of Christians also is projected to rise, but more slowly, at about the same rate (35%) as the global population overall.

As a result, according to the Pew Research projections, by 2050 there will be near parity between Muslims (2.8 billion, or 30% of the population) and Christians (2.9 billion, or 31%), possibly for the first time in history.2

With the exception of Buddhists, all of the world’s major religious groups are poised for at least some growth in absolute numbers in the coming decades. The global Buddhist population is expected to be fairly stable because of low fertility rates and aging populations in countries such as China, Thailand and Japan.

Worldwide, the Hindu population is projected to rise by 34%, from a little over 1 billion to nearly 1.4 billion, roughly keeping pace with overall population growth. Jews, the smallest religious group for which separate projections were made, are expected to grow 16%, from a little less than 14 million in 2010 to 16.1 million worldwide in 2050.

Adherents of various folk religions – including African traditional religions, Chinese folk religions, Native American religions and Australian aboriginal religions – are projected to increase by 11%, from 405 million to nearly 450 million.

And all other religions combined – an umbrella category that includes Baha’is, Jains, Sikhs, Taoists and many smaller faiths – are projected to increase 6%, from a total of approximately 58 million to more than 61 million over the same period.3

While growing in absolute size, however, folk religions, Judaism and “other religions” (the umbrella category considered as a whole) will not keep pace with global population growth. Each of these groups is projected to make up a smaller percentage of the world’s population in 2050 than it did in 2010.4

Similarly, the religiously unaffiliated population is projected to shrink as a percentage of the global population, even though it will increase in absolute number. In 2010, censuses and surveys indicate, there were about 1.1 billion atheists, agnostics and people who do not identify with any particular religion.5 By 2050, the unaffiliated population is expected to exceed 1.2 billion. But, as a share of all the people in the world, those with no religious affiliation are projected to decline from 16% in 2010 to 13% by the middle of this century.

At the same time, however, the unaffiliated are expected to continue to increase as a share of the population in much of Europe and North America. In the United States, for example, the unaffiliated are projected to grow from an estimated 16% of the total population (including children) in 2010 to 26% in 2050.

As the example of the unaffiliated shows, there will be vivid geographic differences in patterns of religious growth in the coming decades. One of the main determinants of that future growth is where each group is geographically concentrated today. Religions with many adherents in developing countries – where birth rates are high, and infant mortality rates generally have been falling – are likely to grow quickly. Much of the worldwide growth of Islam and Christianity, for example, is expected to take place in sub-Saharan Africa. Today’s religiously unaffiliated population, by contrast, is heavily concentrated in places with low fertility and aging populations, such as Europe, North America, China and Japan.

Globally, Muslims have the highest fertility rate, an average of 3.1 children per woman – well above replacement level (2.1), the minimum typically needed to maintain a stable population.6 Christians are second, at 2.7 children per woman. Hindu fertility (2.4) is similar to the global average (2.5). Worldwide, Jewish fertility (2.3 children per woman) also is above replacement level. All the other groups have fertility levels too low to sustain their populations: folk religions (1.8 children per woman), other religions (1.7), the unaffiliated (1.7) and Buddhists (1.6).

Another important determinant of growth is the current age distribution of each religious group – whether its adherents are predominantly young, with their prime childbearing years still ahead, or older and largely past their childbearing years.

In 2010, more than a quarter of the world’s total population (27%) was under the age of 15. But an even higher percentage of Muslims (34%) and Hindus (30%) were younger than 15, while the share of Christians under 15 matched the global average (27%). These bulging youth populations are among the reasons that Muslims are projected to grow faster than the world’s overall population and that Hindus and Christians are projected to roughly keep pace with worldwide population growth.

All the remaining groups have smaller-than-average youth populations, and many of them have disproportionately large numbers of adherents over the age of 59. For example, 11% of the world’s population was at least 60 years old in 2010. But fully 20% of Jews around the world are 60 or older, as are 15% of Buddhists, 14% of Christians, 14% of adherents of other religions (taken as a whole), 13% of the unaffiliated and 11% of adherents of folk religions. By contrast, just 7% of Muslims and 8% of Hindus are in this oldest age category.

In addition to fertility rates and age distributions, religious switching is likely to play a role in the growth of religious groups. But conversion patterns are complex and varied. In some countries, it is fairly common for adults to leave their childhood religion and switch to another faith. In others, changes in religious identity are rare, legally cumbersome or even illegal.

The Pew Research Center projections attempt to incorporate patterns in religious switching in 70 countries where surveys provide information on the number of people who say they no longer belong to the religious group in which they were raised. In the projection model, all directions of switching are possible, and they may be partially offsetting. In the United States, for example, surveys find that some people who were raised with no religious affiliation have switched to become Christians, while some who grew up as Christians have switched to become unaffiliated. These types of patterns are projected to continue as future generations come of age. (For more details on how and where switching was modeled, see the Methodology. For alternative growth scenarios involving either switching in additional countries or no switching at all, see Chapter 1.)

Over the coming decades, Christians are expected to experience the largest net losses from switching. Globally, about 40 million people are projected to switch into Christianity, while 106 million are projected to leave, with most joining the ranks of the religiously unaffiliated. (See chart above.)

All told, the unaffiliated are expected to add 97 million people and lose 36 million via switching, for a net gain of 61 million by 2050. Modest net gains through switching also are expected for Muslims (3 million), adherents of folk religions (3 million) and members of other religions (2 million). Jews are expected to experience a net loss of about 300,000 people due to switching, while Buddhists are expected to lose nearly 3 million.

International migration is another factor that will influence the projected size of religious groups in various regions and countries.

Forecasting future migration patterns is difficult, because migration is often linked to government policies and international events that can change quickly. For this reason, many population projections do not include migration in their models. But working with researchers at the International Institute for Applied Systems Analysis in Laxenburg, Austria, the Pew Research Center has developed an innovative way of using data on past migration patterns to estimate the religious composition of migrant flows in the decades ahead. (For details on how the projections were made, see Chapter 1.)

The impact of migration can be seen in the examples shown in the graph at the right, which compares projection scenarios with and without migration in the regions where it will have the greatest impact. In Europe, for instance, the Muslim share of the population is expected to increase from 5.9% in 2010 to 10.2% in 2050 when migration is taken into account along with other demographic factors that are driving population change, such as fertility rates and age. Without migration, the Muslim share of Europe’s population in 2050 is projected to be nearly two percentage points lower (8.4%). In North America, the Hindu share of the population is expected to nearly double in the decades ahead, from 0.7% in 2010 to 1.3% in 2050, when migration is included in the projection models. Without migration, the Hindu share of the region’s population would remain about the same (0.8%).

In the Middle East and North Africa, the continued migration of Christians into the six Gulf Cooperation Council (GCC) countries (Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates) is expected to offset the exodus of Christians from other countries in the region.7 If migration were not factored into the 2050 projections, the estimated Christian share of the region’s population would drop below 3%. With migration factored in, however, the estimated Christian share is expected to be just above 3% (down from nearly 4% in 2010).

Beyond the Year 2050

Long-Term Projections of Christian and Muslim Shares of World’s PopulationThis report describes how the global religious landscape would change if current demographic trends continue. With each passing year, however, there is a chance that unforeseen events – war, famine, disease, technological innovation, political upheaval, etc. – will alter the size of one religious group or another. Owing to the difficulty of peering more than a few decades into the future, the projections stop at 2050.

Readers may wonder, though, what would happen to the population trajectories highlighted in this report if they were projected into the second half of this century. Given the rapid projected increase from 2010 to 2050 in the Muslim share of the world’s population, would Muslims eventually outnumber Christians? And, if so, when?

The answer depends on continuation of the trends described in Chapter 1. If the main projection model is extended beyond 2050, the Muslim share of the world’s population would equal the Christian share, at roughly 32% each, around 2070. After that, the number of Muslims would exceed the number of Christians, but both religious groups would grow, roughly in tandem, as shown in the graph above. By the year 2100, about 1% more of the world’s population would be Muslim (35%) than Christian (34%).

The projected growth of Muslims and Christians would be driven largely by the continued expansion of Africa’s population. Due to the heavy concentration of Christians and Muslims in this high-fertility region, both groups would increase as a percentage of the global population. Combined, the world’s two largest religious groups would make up more than two-thirds of the global population in 2100 (69%), up from 61% in 2050 and 55% in 2010.

It bears repeating, however, that many factors could alter these trajectories. For example, if a large share of China’s population were to switch to Christianity (as discussed in this sidebar), that shift alone could bolster Christianity’s current position as the world’s most populous religion. Or if disaffiliation were to become common in countries with large Muslim populations – as it is now in some countries with large Christian populations – that trend could slow or reverse the increase in Muslim numbers.

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