Why people with no religion are projected to decline as a share of the world’s population

For years, the percentage of Americans who do not identify with any religion has been rising, a trend similar to what has been happening in much of Europe (including the United Kingdom). Despite this trend, in coming decades, the global share of religiously unaffiliated people is expected to fall, according to the Pew Research Center’s new study on the future of world religion.

To be clear, the total number of religiously unaffiliated people (which includes atheists, agnostics and those who say they have no particular religion on censuses and surveys) is expected to rise, from 1.1 billion in 2010 to 1.2 billion in 2050. But this growth is projected to occur at the same time that other religious groups – and the global population overall – are growing faster.

These projections, which take into account demographic factors such as fertility, age composition and life expectancy, forecast that people with no religion will make up about 13% of the world’s population in 2050, down from roughly 16% as of 2010.

This is largely attributable to the fact that religious “nones” are, on average, older and have fewer children than people who are affiliated with a religion. In 2010, for instance, 28% of people who belong to any of the world’s religions were younger than 15 years old, compared with just 19% of the unaffiliated. And adherents of religions are estimated to give birth to an average of 2.6 children per woman, compared with an average of 1.7 children among the unaffiliated.

Of the 10 countries with the largest unaffiliated populations in the world as of 2010, all are expected to decline as a share of the world’s population by 2050. This list includes the United States and nine countries in Asia or Europe, areas with lower fertility rates and older populations than other parts of the world (including Africa and the Middle East).

The projection model also considers religious switching, or conversion, for 70 countries with reliable switching data. Religious switching has been powering the rise of the “nones” in the United States and Europe, and a net gain globally of more than 60 million people are projected to join the ranks of the unaffiliated through religious switching between 2010 and 2050.

Some social theorists have suggested that as countries develop economically, more of their residents will move away from religious affiliation, as has been seen in Europe. But there is little evidence of such a phenomenon in Muslim-majority countries. Moreover, in Hindu-majority India, religious affiliation is still nearly universal despite rapid economic and social change.

China, with its large population and lack of reliable data on religious switching, is something of a wild card when it comes to the future of world religion. This is especially true for the religiously unaffiliated population; more than half of the world’s people who do not identify with any religion live in China (roughly 700 million).

Some experts believe the Christian population in China is rising while the religiously unaffiliated population is falling. If this is true – and the trend continues – religious “nones” could decline as a share of the world’s population even more than the Pew Research Center study projects.