It appears that the decline of religion is not the wave of the future. Despite the decades of predictions by some Western atheists and agnostics that religion would die out (remember hearing that when you were in school?), there is no evidence to support that belief.
Actually, religion is growing stronger and the unaffiliated* (including atheists and agnostics) weaker.
Right now the unaffiliated are slightly more than Hindus in world population and percentage. In 2050 the projection is that the unaffiliated will lag behind Hinduism. Hinduism is expected to lose less than a percent of their current share (from 15% to 14.9%). Atheists and agnostics by contrast are expected to shed about 1/5th of their 2010 world footprint (16.4% to 13.2%).
|2010 to 2050: box on the left shows population in billions; box on the right percentage growth/loss|
Pew Research Center, April 2, 2015
what happens in China will have a huge impact since presently China has the largest unaffiliated population in the world (62% of the 1.1 billion total).
The biggest unknown factor, however, is China, the world’s most populous country. Because of a lack of reliable data on religious switching in China, none of the scenarios models religious switching among its 1.3 billion people. If there is considerable switching in China in the coming decades, it could lower the percentage of the world’s population that is unaffiliated and boost the numbers of Christians, Buddhists and perhaps other groups.However, there is some light for unaffiliateds in six countries: Japan, the United States, Vietnam, Germany, France and the United Kingdom. But, the cloud coming with that silver lining is that those countries and the other four countries with a large unaffiliated population are on target to reduce their population share from 1/3rd of the world's population in 2010 to 1/4th in 2050.
The religiously unaffiliated are heavily concentrated in relatively few countries. As of 2010, about 86% lived in the 10 countries with the largest unaffiliated populations.[see side chart] Consequently, the demographic trajectory of these countries will help shape the projected size of the global unaffiliated population in the decades to come.
In 2010, more than six-in-ten (62%) of the world’s religiously unaffiliated people lived in China. The next largest religiously unaffiliated populations were in Japan (6% of the global total), the United States (5%), Vietnam (2%) and Russia (2%).
In 2050, China is expected to remain home to a majority (54%) of the world’s unaffiliated population. The United States is expected to have the world’s second-largest unaffiliated population (8%), surpassing Japan (6%)._____
*Pew definies the unaffiliated as "atheists, agnostics and people who do not identify with any particular religion"