Understanding potential and emerging patterns in population levels is essential for anyone tasked with planning for a society's changing age structures, the healthcare resources that would involve, and their impact on the economic landscape. When longevity in Singapore exceeds that of Japan, it is a cause for not only celebration but also introspection: how to support the growing number of elderly and give them meaningful lives; how to structure insurance and schemes to account for longer lifespans. Will there be enough productive young people to fund the comfortable existence of the elderly? Should nations plan for immigration if the resident population fails to produce enough babies of its own?

For this reason, a study published last week in The Lancet medical journal is worthy of attention. The study by the Institute for Health Metrics and Evaluation at the University of Washington challenges assertions by United Nations demographers, including one that projected world population peaking at 10.9 billion by the end of the century, from about 7.8 billion today. The study sees the peak at 9.7 billion by 2064, with steady declines to 8.8 billion by 2100. By this projection, the number of Thais, Japanese, Italians, Spaniards and people in 19 other nations could shrink by more than half. What's more, China and India could see steep falls in working-age population, thus crimping their global economic clout.