The Great Falling Away - It's Real, It's Here

"...people are leaving Christianity in droves. About 106 million Christians are expected to switch affiliation from 2010 to 2050 while only about 40 million people are expected to enter Christianity.

The religiously unaffiliated (athiests, agnostics) are expected to see the largest net gains from switching, adding more than 61 million followers.

See the full article at Business Insider.