Yeah, I've heard about this before
. Low birth rates in North America and Europe and much higher (but slowly declining) birth rates in the 3rd world are going to create a bulge of Muslims and mask the decline of Christianity in the West with gains in the 3rd world. "Much of the worldwide growth of Islam and Christianity, for example, is expected to take place in sub-Saharan Africa.", and more than half of the population growth is expected to come from Africa. This population bulge in Africa is expected to level off
as annual population growth numbers decline from 2.5% in 2010 to 1% in 2100.
So yes, there will be a temporary surge of theists in the world. However, the unaffiliated category continues to gain ground in the West. In fact, by 2050, the largest "religious" group in France, Netherlands, and New Zealand is projected to be unaffiliated. And 1 in 4 Europeans will likely be unaffiliated. Same deal in the United States and Canada.
I've seen theists *coughRandy*cough* try to use these figures to claim that atheism is dying out. If you take a very cursory glance it and you're not big on reading further or thinking too hard, it might look like western atheists are doomed. But a closer look shows that they're not.