Sub-Saharan Africa has replaced Europe as the locus for the world’s Christians, due to both higher birthrates and Western Europe’s “widespread Christian disaffiliation” — with Christians declining as a share of the world’s population due to adherents leaving the faith, according to new research by the Pew Research Center.

Christians, tallied across denominations, remain the world’s largest religious group — a majority in all regions except the Asia-Pacific, Middle East and North Africa areas — but “they are shrinking as a share of the global population, as large numbers of Christians around the world ‘switch’ out of religion to become religiously unaffiliated,” said Pew.

While the total number of Christians in the world increased from 2.1 billion to 2.3 billion during the decade from 2010-2020, the total population of non-Christians grew by 15 per cent to 5.6 billion.

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“As a result, Christians shrank as a percentage of the global population, with their share falling from 31 per cent to 29 per cent,” Pew said.

On June 9, the centre released “How the Global Religious Landscape Changed from 2010 to 2020.” The data, drawn from more than 2,700 sources, including national censuses, large-scale demographic and population surveys as well as population registers, represents 201 countries and territories with populations of at least 100,000.

Seven broad categories are named in the report: Christians, Muslims, Hindus, Buddhists, Jews, other religions (including, among others, Baha’is, Sikhs, Zoroastrians and Wiccans) and those who are religiously unaffiliated.

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A number of factors influence religious demographics, such as fertility, mortality, migration and religious switching, which Pew defines as changing in adulthood from a childhood religious group to another, or disaffiliating from religion altogether. Ultimately, fertility and religious switching have proven decisive in shaping global religious demographics, Pew said, noting that migration cannot change the size of the global population of a given religious group, and that migrants tend to settle in nations where their religious identity is prevalent.

In sub-Saharan Africa, the overall population grew to 1.1 billion from 2010-2020, with most people (62 per cent) in the region identifying as Christians, said Pew. The report also noted that the region’s younger demographics and higher fertility rates drove religious growth among all groups except for Jews, with the entire region accounting for “most of the increase in Christian numbers, globally.”

In the new study, Pew said that while “Christians have a high fertility rate … they have been losing adherents as people switch out of Christianity to become religiously unaffiliated.” Religious switching is generally completed by the end of a person’s young adult years, said Pew, citing various studies.

Religiously unaffiliated persons made for the third largest category among the global population, behind Christians and Muslims, said Pew.

As of 2020, Christians remained a majority in 120 countries and territories, down from 124 in 2010. Among the nations where Christians represent less than half the population are the United Kingdom (49 per cent), Australia (47 per cent), France (46 per cent) and Uruguay (44 per cent), all of which now have 40 per cent or more residents identifying themselves as religiously unaffiliated.

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Canada, the study showed, has experienced a notable 2010-2020 downturn in self-identified Christians, from 67.2 per cent to 53.3 per cent.

Overall, Christians and Buddhists saw the greatest losses due to religious switching.