Islam grows, Christianity slips as share of world population: Pew Research Center

Islam has increased its share of the world population, the Pew Research Center found in a report released Monday.

The Muslim population increased by 1.8 percentage points to 25.6 percent, according to the report.

The report examined changes in religious demographics through an analysis of more than 2,700 censuses and surveys.

While Christians remained the world's largest religious group in 2020, Christianity's growth did not keep up with global population increase, reports the Washington Post. 

The overall number of Christians climbed to 2.3 billion, but the religion's share of the world's population decreased by 1.8 percentage points to 28.8 percent. 

"It's just striking that there was such dramatic change in a 10-year period," said Pew's Conrad Hackett, the lead author of the report. 

"During this time, the Muslim and Christian populations grew closer in size. Muslims grew faster than any other major religion."

The growth in Islam was due to a younger Muslim population — with an average age of about 24, as opposed to a global average age among non-Muslims of about 33 as of 2020, said the report. 

This occurred alongside higher fertility rates in some areas and lower rates of disaffiliation as compared with other religions, including Christianity, Washington Post said. 

"Among young adults, for every person around the world who becomes Christian, there are three people who are raised Christian who leave," Hackett said.

The largest share of Christians — about 31 percent — can be found in sub-Saharan Africa, according to the study. Previously, Europe was home to the largest number of Christians in the world.

"And that's the result of high fertility, youthfulness and rapid growth in general of sub-Saharan Africa," Hackett said, "as well as the aging, lower fertility and disaffiliation going on in Europe."

Religion switching — seen in high numbers among Christians — contributed to the global rise of unaffiliated people, the report found. 

People leaving religion, and especially departing Christianity, has led to the increase of the unaffiliated population, Hackett said.

"Sometimes we hear rumors of religious revival, and it's certainly possible that in particular places religion could grow," Hackett said. "But in this careful 10-year study that we've done, the broad trend is that in many places people are moving away from religion."

Based on patterns of religion switching and differences in age and fertility, Hackett estimated that the "movement towards convergence" between Christians and Muslims will continue, with Islam set to grow to become the world's largest religion in the years ahead, unless trend lines shift.