By 2050, only 13 percent of the world’s population would not be religiously affiliated, as opposed to over 16 percent in 2010, according to a new Pew Research Center study published Thursday. The survey, which forecast a rise in the number of religious people globally over the next three decades, said that by 2050, the ranks of all major religions, expect Buddhism, would expand -- with Islam leading the trend.

According to the study, by 2050, perhaps for the first time in history, the number of Muslims would nearly equal the number of Christians. While Christianity would remain the world’s largest religion, with 2.92 billion believers, the population of Muslims would grow rapidly -- from 1.6 billion in 2010 to 2.76 billion in 2050.

 Projected Change in Global Population

“If current demographic trends continue, Islam will nearly catch up by the middle of the 21st century,” the Washington-based think tank said in the study. “Between 2010 and 2050, the world’s total population is expected to rise to 9.3 billion, a 35 percent increase. Over that same period, Muslims -- a comparatively youthful population with high fertility rates -- are projected to increase by 73 percent. The number of Christians also is projected to rise, but more slowly, at about the same rate as the global population overall.”

As a result, by 2050, more than 6 out of 10 people on the planet will be either Christian or Muslim.

If these predictions pan out, Islam would be the only religion to surpass the global rate of population expansion. Muslims will also surpass Jews as the largest non-Christian population in the U.S., according to the study. Moreover, Muslims are expected to make up more than 50 percent of the population in 51 countries by 2050 and India will have the largest Muslim population in the world, surpassing Indonesia.

Islam Growing Fastest

In the same time period, the population of non-believers -- atheists, agnostics and people who do not identify with any particular religion -- is forecast to increase by merely 100 million -- from 1.1 billion in 2010 to 1.2 billion in 2050. In percentage terms, this would mean a drop from 16 percent of the global population in 2010 to 13 percent of the population in 2050.

However, in many countries across Europe and North America, the population of religiously unaffiliated is projected to increase as a share of the population. In the U.S., for example, their population would grow from 16 percent in 2010 to 26 percent in 2050.

Projected Change in the Unaffiliated Population, 2010-2050

According to the study, these shifts in the world's religions are the result of several factors, including differences in fertility rates, the size of the youth population and because of people switching faiths.

“Globally, Muslims have the highest fertility rate, an average of 3.1 children per woman -- well above replacement level (2.1), the minimum typically needed to maintain a stable population. Christians are second, at 2.7 children per woman,” the survey found. Buddhists have the lowest fertility rate of 1.6, and, as a result, their population is expected to decline from 7.1 percent in 2010 to 5.2 percent in 2050.

However, Pew warned, the predictions are based on current demographic trends, which can change due to several unforeseen events such as war, famine, political turmoil and economic meltdowns, and can throw the numbers off.

“Some social theorists have suggested that as countries develop economically, more of their inhabitants will move away from religious affiliation. While that has been the general experience in some parts of the world, notably Europe, it is not yet clear whether it is a universal pattern,” the authors of the study said. “In any case, the projections in this report are not based on theories about economic development leading to secularization.”