The world is heading for demographic catastrophe. Fertility rates have been falling across the globe for 40 years, to the point where, today, Israel is the only First World country where women have enough babies to sustain their population. The developing world is heading in the same direction, fast. Only 3 percent of the world's population live in a country where the fertility rate is not dropping.
As fertility falls, populations shrink. As populations shrink, economies will sputter. Western countries will struggle to support too many retirees without enough workers, and the rest of the world (particularly places such as China and Russia) will be challenged just to maintain order as societies change in unprecedented ways: Most people will have neither brothers, sisters, aunts, nor uncles, and there will be no such thing as an extended family.
This forecast may sound apocalyptic, but it's nearly conventional wisdom among the demographers and economists who study such things.
On the positive side, for this country at least, if current trends continue, America has a chance to actually be more religious in 2050 than today. The least secular people in this country are having the most children (have you ever met a Christian home schooler?!). In general the most conservative states have the highest fertility rates and anecdotal evidence suggests that a younger generation of devout Christians are trying to have more children, not fewer. A silver lining perhaps.