The demographic future for the U.S. and the world looks very different than the recent past in key respects. Growth from 1950 to 2010 was rapid—the global population nearly tripled, and the U.S. population doubled. However, population growth from 2010 to 2050 is projected to be significantly slower and is expected to tilt strongly to the oldest age groups, both globally and in the U.S.
Aging is not exactly news—the U.S. and global populations also turned older from 1950 to 2010. But future prospects for aging have garnered more attention because, unlike in the past, younger populations, those of children and those of middle-age adults, are at near standstill. Thus, the social and economic effects of aging are likely to be felt more acutely in the future.
Population Change
The projected slowdown in population growth is even sharper in the world overall. From 1950 to 2010, the world population increased from 2.5 billion to 6.9 billion, or by 174%. The average annual rate of growth—1.7%—was much higher than in the U.S. In the future, the global population is expected to increase from 6.9 billion in 2010 to 9.6 billion in 2050, or by 38%. The average annual rate of growth—0.8%—is only slightly higher than the rate projected for the U.S.
Birth Rates, Death Rates, and Life Expectancy
From 1950 to 1955, the crude birth rate in the U.S. averaged 24.4 per 1,000 people. That was more than double the crude death rate of 9.6 per 1,000 people. Thus, population growth was more robust in the past. By 2010-2015, the crude birth rate in the U.S. had fallen to 13.2, much closer to the crude death rate of 8.3. By mid-century, from 2050 to 2055, the birth rate is projected to drop further to 12.2 and the death rate to rise to 10.2. Consequently, population growth from 2010 to 2050 should be much slower than it was from 1950 to 2010.
The decrease in birth rates around the world is linked to a number of factors. These include social trends, such as the decline in marriage rates and the movement away from the family as a core living arrangement, and economic forces, such as the rising cost of raising children, the growing number of women in college and in the labor force, urbanization and, with the emergence of social insurance, the reduced need for children as a support mechanism in old age. Development of the contraceptive pill and its widespread adoption starting in the 1960s is also a factor. Government policies, such as China’s imposition of a one-child policy in 1979, also may have played a role.
The gains in longevity were initially due to reductions in infant mortality. Those, in turn, were driven by better sanitation, improvements in public health, and advances in overcoming childhood diseases, such as smallpox, polio and measles. General improvements in living standards and nutrition and changes in health-related behaviors have also been factors. In more recent decades, gains in life expectancy are increasingly being realized at older ages. That is the consequence of medical advances against heart disease, cancer and other adult afflictions. This phenomenon has been dubbed the “longevity transition.”
Population Change by Age Group
Even in the past, the rate of growth in the population of seniors (ages 65 and older) exceeded the rate of growth in the populations of younger cohorts. In the U.S., the population of seniors more than tripled, from 13 million in 1950 to 40.8 million in 2010, a total gain of 213%. The percentage increase was greater than the increase in the population of 15- to 64-year- olds (105%) and the increase in the population of children younger than 15 (45%).
A similar trend characterized changes in the global population by age groups. The global population of those 65 years and older more than quadrupled, from 128.4 million in 1950 to 530.5 million in 2010. That was a gain of 313%, significantly greater than the increase of 197% among 15- to 64-year-olds and 112% among children younger than 15.
The key distinction between the past and the future is that the growth in the population of young children virtually grinds to a halt through the middle of the century. Estimates indicate that the global population of children younger than 15 will increase by only 10% from 2010 to 2050. The U.S. will likely experience more growth—17% in total from 2010 to 2050—but at the modest rate of 0.4% annually.
The future may also feature steep drop-offs in the rates of growth of 15- to 64-year-olds. From 1950 to 2010, this age cohort grew at an annual rate of 1.2% in the U.S. and at an annual rate of 1.8% in the world overall. The annual rates of growth are projected to be only one-third as high from 2010 to 2050—0.4% in the U.S. and 0.7% globally.
Similar to the projections for the U.S., the global increase in the population ages 65 and older is expected to account for 36% of the overall increase of 2.6 billion from 2010 to 2050. This, too, stands in sharp relief with the past, when this age cohort accounted for only 9% of the increase in the global population from 1950 to 2010.
Changes in the Age Structures of the U.S. and Global Populations
In the future, however, the world is projected to age more rapidly than the U.S. The median age in the U.S. should rise moderately, from 37 in 2010 to 41 in 2050. The increase in the global median age likely will be sharper, from 29 in 2010 to 36 in 2050.
As the world population turns older at a faster clip, the U.S. share in the global population of seniors should diminish. In 1950, the U.S. was home to 10.2% of the world’s seniors. That share had slipped to 7.7% by 2010 and is projected to drop further to 5.8% by 2050.
In a reversal of past trends, the share of children younger than 15 who live in the U.S. may nudge up, from 3.4% to 3.6%.
Dependency Ratios in the U.S. and Globally
That is partly due to the aging of baby boomers and partly due to the drop-off in population growth. However, because the child and middle-age populations in the U.S. are expected to increase at about the same pace, the child dependency ratio in the U.S. will be unchanged at 30 from 2010 to 2050. Thus, the future increase in the total dependency ratio in the U.S.—from 49 dependents per 100 working-age people in 2010 to 66 in 2050—is driven by aging.
The increase in the old-age dependency ratio in the U.S. is not a new phenomenon. The ratio previously rose from 13 in 1950 to 19 in 2010. However, the child dependency ratio fell sharply in the past, from 42 in 1950 to 30 in 2010. That was the consequence of tumbling birth rates in the wake of a baby boom-fueled bulge in the middle of the U.S. age distribution. Thus, despite an overall aging of the population, the number of dependents per 100 working-age people in the U.S. fell from 54 in 1950 to 49 in 2010.