Population Imbalances: Their Implications for Population Growth over the Twenty-first Century

Current population dynamics vary markedly among countries. In 2010, 46 per cent of the world population lived in countries with below-replacement fertility, whose populations are experiencing rapid population ageing and will likely decrease in the future. In sharp contrast, 19 per cent of the world population lived in countries with such high fertility that their combined populations are likely to double by 2050 and to keep growing over the rest of the century. The remaining 35 per cent lived in countries where fertility levels had declined considerably since their peak but where the potential for continued population growth over the medium term remains high. Owing to both population momentum and the long-standing differences in population dynamics between those groups of countries, these diverse population trends are expected to continue over the medium term, thus maintaining today’s population imbalances and producing a high potential for marked population growth over the course of this century, especially in some of the world’s poorest countries. Reducing those population imbalances by the end of the century and achieving the stabilization of the world’s population requires that the high-fertility countries accelerate the reduction of fertility so that it reaches below-replacement level before 2100.