The steady slowdown in world population growth in recent decades has dimmed interest in what was once called "the population question." But now concern, even alarm, about global population growth may have been reawakened by a widely publicized new study in the journal Science.

The study warns that the current expert consensus, which envisions the world's population stabilizing over the coming century, is likely wrong. Applying elegant and innovative demographic techniques for long-range population projections, the...