“Still the greatest amount of change in the U.S., we think currently and in the future, will come from switching,” he said.
Researchers stressed the report contained projections based on data and mathematical models, not predictions of the future.
“Though some scenarios are more plausible than others, the future is uncertain, and it is possible for the religious composition of the United States in 2070 to fall outside the ranges projected,” they wrote.
One reason for the decline among Christians and the growth among the nones in the models is age. While Christians have more children than nones, they are also older. Pew estimates the average Christian in the United States is 43, which is 10 years older than the average none.
“The unaffiliated are having and raising unaffiliated children while Christians are more likely to be near the end of their lives than others,” Stephanie Kramer, a senior researcher at Pew, told RNS in an email.
Using mathematical models, Pew has also projected the future of religion around the world. Those models were adapted for different regions, said Hackett. Muslims, for example, he said, tend to have the youngest population and the highest fertility rates, driving the growth of that faith. However, he said, in the Gulf states, migration has brought many Christians from other countries to the region as temporary workers.
The current report takes advantage of the amount of data collected about the U.S. religious landscape. Researchers also looked at intergenerational transmission for the first time, said Kramer.
“The variables we use to study that were: What is the mother’s religion? And what is the teen’s religion,” she said. “If that was a match, we consider the mother’s religion transmitted.”
Researchers also looked at a relatively new trend of disaffiliation among older Americans. Sociologists have long focused on younger people, who are most likely to switch religions. But in the U.S. and other countries, older people are also starting to switch at growing rates.
“It’s not as large scale, but it’s still significant,” said Hackett. “And it’s contributing to the religious change that we have experienced and that we expect to experience in the years ahead.”
Hackett said that the projections do not show the end of Christianity in the U.S. or of religion in general, which he expects to remain robust. And most nones, while claiming no religion, do not identify as atheists.
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