World Population in 2050: Assessing the Projections

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This paper will review some population projections for the United States, the world, and selected major regions. The total population size, the youth dependency ratio, the elderly dependency ratio, and the total dependency ratio will receive most attention. The underlying assumptions regarding fertility, mortality, and migration will be reviewed. Projections from different sources will be compared where possible.

But before looking to the future, I thought that it would be useful to have a glimpse into the past. Two thousand years ago, we had about a quarter of a billion people on the planet. It took sixteen to seventeen centuries to double to about one-half billion. The next doubling took less than two centuries, from the middle of the seventeenth century to around 1800. The next doubling took little over 100 years, and standing where we are now and looking back, the last doubling took about thirty-nine years. The second half of the twentieth century is the first time in all of human history in which the Earth’s population doubled within a single lifetime. That is a fortyfold acceleration in the population growth rate, and there is no precedent for that