The Future of the Religiously Unaffiliated

The Pew Research Center just released some new projections of the growth of the religiously unaffiliated.  Read their summary here.  The first two paragraphs give the basic picture (italics added):

During the next few decades, the number of religiously unaffiliated people around the world is projected to grow modestly, rising from about 1.1 billion in 2010 to a peak of more than 1.2 billion in 2040 and then dropping back slightly.42 Over the same 40-year period, however, the overall global population is expected to increase at a much faster pace. As a result, the percentage of the world’s population that is unaffiliated is expected to drop, from 16% of the world’s total population in 2010 to 13% in 2050.

This decline is largely due to the advanced age and low fertility of religiously unaffiliated people globally relative to other religious groups. The three largest unaffiliated populations live in China, Japan and the United States; there also are significant numbers of religiously unaffiliated people in many European countries. All of these areas have older populations and lower fertility rates than the global population overall.

Some questions for you to consider:  Why is the Asia-Pacific region the region with the highest proportion of religiously unaffiliated population?  In which few countries are the religiously unaffiliated are heavily concentrated?  How do different fertility rates between the religiously affiliated and the religiously unaffiliated factor into the projections?  Does accounting for religious switching have a large impact on the projections?