Is "No Religion" world's fastest growing religion?

Question

This recent article from anonhq.com has been widely shared on Facebook.

It claims:

A recent global survey conducted by National Geographic shows that the worlds fastest growing religion is not Islam or Christianity, but no religion at all – atheism.

However, the cited article from National Geographic makes a much weaker claim.

The religiously unaffiliated, called "nones," are growing significantly. They’re the second largest religious group in North America and most of Europe. In the United States, nones make up almost a quarter of the population. In the past decade, U.S. nones have overtaken Catholics, mainline protestants, and all followers of non-Christian faiths.

National Geographic makes a firmer distinction between "nones" and atheists.

Within the ranks of the unaffiliated, divisions run deep. Some are avowed atheists. Others are agnostic. And many more simply don’t care to state a preference.

Are the stronger claims that the number of religiously unaffiliated people is growing faster (in absolute terms) than any religion?

Answer 1

The data for this claim comes from a 2015 study by the Pew Research Center, one of the leading groups analyzing religious demographics.

However, the claim being made is in direct contradiction to the study's subtitle:

Why Muslims Are Rising Fastest and the Unaffiliated Are Shrinking as a Share of the World’s Population

Where does the Anon News claim come from? The National Geographic article it quotes focuses on the secularization of Western Europe, Australia and North America. This is a well-known demographic trend that has been tracked and analyzed since the late 1960s.

Some researchers at that time expected that the entire world would secularize, so the data collection in other regions of the world had to be accordingly careful. The result disproved the universality of the thesis (same source):

Similarly, the religiously unaffiliated population is projected to shrink as a percentage of the global population, even though it will increase in absolute number. In 2010, censuses and surveys indicate, there were about 1.1 billion atheists, agnostics and people who do not identify with any particular religion. By 2050, the unaffiliated population is expected to exceed 1.2 billion. But, as a share of all the people in the world, those with no religious affiliation are projected to decline from 16% in 2010 to 13% by the middle of this century.

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.

But this does not make "no religion" the fastest growing group even in the West, as the numbers of Muslims and Hindus are expected to roughly double from immigration. The claim is completely false.