Scenarios for the World Population in the Next Century: Excessive Growth or Extreme Aging

For six major regions of the world, ten alternative scenarios on future fertility and mortality trends are defined and projections performed from the base year 1985 up to the year 2100. Because of the great inertia of population changes, for the next 20-30 years the scenarios based on widely diverging assumptions do not produce very different patterns. In the longer run, however, the assumption of constant fertility and mortality rates resulting in continued exponential growth yields a total population size of 15 billion in 2050 and even 39 billion in 2100. The immediate replacement fertility scenario, on the other hand, would result in 7.5 billion by 2050. This still means an addition of more than two billion people to today's population of 5.3, which is entirely due to the momentum of population growth. Another major finding is that further aging of the population structure is inevitable even under constant rates. In the case of successful curbing of population growth, aging would be extremely rapid. For example, in Africa under the immediate replacement scenario the mean age of the population would increase from presently 22.2 years to more than 40 years by 2050. More moderate scenarios also result in very significant aging.