This data is from Atheistrepublic.com whom I've been supporting in for almost 2 years, they have a reliable sources when it is related with religion.
Shifting global religious trends.
In 2012, the internet was abuzz with a bevy of articles, blog posts and conversations about something new happening in American religion - it was dying. Religious people were horrified and spurred to action. Atheists were calling it a new era of secularism. The media was calling it the "rise of the nones" (Americans who were reporting to claim no religion).
All of this was brought on by a 2012 report by the Pew Research Center revealing that one-in-five American adults (one-third of those 18-30) claim no religion. This was following a 2002 report by sociologists Michael Hout and Claude Fischer, that in the 1990s, Americans who claim no religion doubled from 7% to 14%. Both reports combined indicated a rather rapid decline in religious engagement in America from the 90s to 2012, especially amongst the younger generation.
The numbers however, didn't seem to jibe with actual human behavior. So, on August 8, 2013, Pew put together a panel to discuss with journalists, scholars, and other stakeholders, these and other important trends in American religious life.
An important qualification to make right away when discussing the nones, is that Americans remain the most religious people of the Protestant Western nations, and that over the long run, church membership and activity have seen a net increase. Religious involvement in America is still higher than it was 100 years ago. When Americans leave their church, they typically relocate to a different one. The difficulty in acquiring an accurate count of nonreligious people globally has a lot to do with separating culture and politics from religion, as well as a number of places expressing open hostility toward the nonreligious.
What become clear between 2002 and 2012, is that there was a generational trend of claiming no religion, but not necessarily a strong trend toward rejecting god. Much of the discussion surrounding these numbers was related to an overall trend away from rigid organized structures of hierarchy and authority, leading 18-30 year olds away from "religion" even though they don't seem to be denying the existence of god. There also appeared to be a weakening in conviction surrounding certain Christian beliefs such as the Bible being the literal Word of God, the existence of a literal and eternal physical hell, and a variety of religious mores such as the "sinfulness" of same-sex attraction, premarital sex, etc.
Frank Newport, Editor-in-Chief of Gallup put it this way, "[...]But when we asked religious identity, in some ways it's different because we're asking people to publicly put a label on themselves in a given arena, and I think that there - and that's what I want to talk about here, is that part of what we may be seeing here is a change in the way that people choose to label themselves, rather than something which represents a more fundamental change in some of the other measures of religiosity that we can look at."
Claude Fischer, Professor of Sociology, University of California, Berkeley, summarized, "[...]that group of people who weren't very closely tied to religion in the first place are now increasingly making a declaration that they're not religious.[...]"
Basically, the percentage of Americans who consider religion to be very important hadn't changed much. But the people for whom religion was not very important, had been switching their label from "not very religious" to "no religious affiliation." What we saw was most likely a change in the way younger people were labeling themselves as opposed to a change in the substance of their beliefs.
This assessment seems to have been confirmed in a newer report* that came out early in 2015, also by Pew, titled “The Future of World Religions: Population Growth Projections, 2010-2050.” It asserts that “Muslims Are Rising Fastest and the Unaffiliated Are Shrinking as a Share of the World’s Population.”
In short, the claim is that if current trends continue, Islam will nearly catch up to Christianity by the middle of the 21st century; likely due to shifts in fertility rates and the youth population as well as people shifting faiths.
In some places like America and France, the nones are continuing to grow, but these numbers are not outpacing the trends worldwide. And in America, Judaism will no longer be the largest non-Christian religion. The number of Christians is expected to continue to grow but at a much slower pace than Islam.
In addition, all of the world’s major religious groups (except Buddhism) are expected to grow in absolute numbers, including folk religions. However, these numbers are not expected to match population growth so each religion will make up a smaller percentage of the population.
The report mentions several times that the main reason for the apparent growth in Islam worldwide is that their adherents are relatively young, with their childbearing years ahead of them, and they have a high rate of reproduction than other major religions, thus allowing Islam to outpace population growth. In other words, Christianity, Judaism, Buddhism and “other” religions are essentially “aging out” of the growth pool.
How does this affect the numbers for the religiously unaffiliated? This group is projected to shrink as a percentage of the global population, even though it will increase in absolute number. At the same time, however, the unaffiliated are expected to continue to increase as a share of the population in much of Europe and North America. In the United States, for example, the unaffiliated are projected to grow from an estimated 16% of the total population (including children) in 2010 to 26% in 2050.
- “Demographers at the Pew Research Center in Washington, D.C., and the International Institute for Applied Systems Analysis (IIASA) in Laxenburg, Austria, gathered the input data from more than 2,500 censuses, surveys and population registers, an effort that has taken six years and will continue.
The projections cover eight major groups: Buddhists, Christians, Hindus, Jews, Muslims, adherents of folk religions, adherents of other religions and the unaffiliated.”