population momentum

Population momentum refers to the continued growth or decline of a population even after birth rates decline to replacement level. This occurs because of the age structure of the population; when many people are young, there are still many potential parents who will have children, leading to future population increases. Conversely, if the population is aging, growth may slow even if birth rates are stable. Essentially, momentum reflects how the current age distribution influences future population trends, making population changes lag behind changes in fertility rates.