Population Momentum Transition

In the developing world it is expected that half of the future population growth will be caused by its young population age-structure, an aspect of population dynamics that is referred to as population momentum. Less discussed is the amount of population decline that will be observed in the future in developed countries with its “negative momentum” caused by its old population age-structure. Population momentum summarizes the relation between a population age-structure and the age-structure resulting from its equivalent population under stability (growth equal to zero). Since mortality and fertility change permanently also the population momentum corresponding for each time is different. However, little work has been done to summarize time trends of this measure. We study the trends in time of population momentum for countries with available period and cohort, fertility and mortality information. Our preliminary results show clear distinction between three periods in population momentum, distinguish by their levels of fertility and mortality: high-high, high-low, and low-low, for fertility and mortality respectively. In recent years most developed countries have entered into the low-low stage and more than a decade of negative population momentum.