Islam is the fastest growing faith tradition and is expected to nearly equal Christianity in 40 years, according to a Pew Research Center study.
Pew is projecting that Islam will increase from 1.6 billion followers (2010) to 2.76 billion (2050) while Christianity would increase from 2.17 billion to 2.92 billion.
This would mean that the percentage of Christians in the world would remain at 2010 levels, while the percentage of Muslims would increase by 6.5 percent.
The global population is expected to reach 9.3 billion by 2050, a 35 percent increase.
Looking even further into the future, Pew expects Islam and Christianity to represent an equal percentage of the global population by 2070, with Islam surpassing Christianity by 2100.
While the religiously unaffiliated have increased in certain countries, this group is expected to decline as a percentage of the global population.
The study is projecting that this group will grow from 1.13 billion (2010) to 1.23 billion (2050), which would mean a decrease of 3.2 percent in their share of the global population.
In the U.S., however, Pew expects the religiously unaffiliated to represent 26 percent of the population by 2050, a 10 percent increase.
Geography was a leading influence on future growth, the report noted.
“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.”
The full report, available here, also discusses the impact of migration and switching of religious traditions on each group’s future growth.