Pew Research has released a report on global trends in religious affiliation. If the current trends continue by 2050 …
- The number of Muslims will nearly equal the number of Christians around the world.
- Atheists, agnostics and other people who do not affiliate with any religion – though increasing in countries such as the United States and France – will make up a declining share of the world’s total population.
- The global Buddhist population will be about the same size it was in 2010, while the Hindu and Jewish populations will be larger than they are today.
- In Europe, Muslims will make up 10% of the overall population.
- India will retain a Hindu majority but also will have the largest Muslim population of any country in the world, surpassing Indonesia.
- In the United States, Christians will decline from more than three-quarters of the population in 2010 to two-thirds in 2050, and Judaism will no longer be the largest non-Christian religion. Muslims will be more numerous in the U.S. than people who identify as Jewish on the basis of religion.
- Four out of every 10 Christians in the world will live in sub-Saharan Africa.
Christianity Today has a good overview of the findings including some alternative predictions.
Here's the full report: 2010-2050 World Religious Trends - Pew Research
UPDATE: The 2015 figures from the IBMR: Global Christianity 2015 in the Context of 1900–2050
UPDATE: The Center for the Study of Global Christianity responds to the Pew Research findings.