We’re not getting any younger, you know. Humanity, that is. According to a sweeping new report from the U.S. Census Bureau, people 65 and older will soon outnumber children under 5 for the first in human history. The proportion of global senior citizens, now at 8.5 percent, will double to 16.7 percent by 2050 and continue to grow for the foreseeable future. At the same time, the proportion of young children will decrease to just 7.2 percent of the world population.

This aging phenomena is due to both an increase in life expectancy and declining fertility rates in much of the world. The report notes the huge disparities between the oldest and youngest countries. In 2015, Japan ranked as the oldest country with 26.6 percent of the population 65 or older. Not surprisingly, Japan also enjoys the oldest life expectancy at nearly 85 years and a low fertility rate (1.4 child average). On the other end of the spectrum is Qatar and the United Arab Emirates, where only one percent of the population is at least 65.

Another way to examine the age structure of a population is by looking at the median age. Japan and Germany are the most mature with a median age of 47, while Sub-Saharan countries (including Niger, Uganda and Mali) have median ages of just 15-16.

In examining our aging world, the authors consider a range of health trends (from obesity and smoking to HIV), access and quality of health care and economic factors that affect retirement age and elderly care worldwide.

A classroom discussion of these aging trends would be an excellent follow-up to one of our “population pyramid” activities like The Power of the Pyramids. There, students can visualize the data with each horizontal bar representing a 5-year age cohort shown on the graphs for each country. Keep in mind, though, that the top bar (expressed as 75+ in our activity) represents many more years, especially as life expectancy grows.

Combining the pyramid activity with the data from the Census report can also lead to an examination of the likely consequences of an aging populace. These might include challenges such as the costs of caring for more seniors. But, students may also consider the benefits, such as an eventual stable population that can better meet the health, educational and environmental needs of humanity. Some of these themes are explored in a new book, The Good Crisis: How Population Stabilization Can Foster a Healthy U.S. Economy, a collection of essays by 15 prominent academics and journalists that charts a path to prosperity and sustainability in an aging society.