Graphing global population trends

This exercise is a part of Educator Guide: Human Population Hits a Milestone / View Guide
Directions for teachers:

Ask students to read the Science News article “The world population has now reached 8 billion” and answer the following questions. A version of the article, “Human population hits a milestone,” appears in the December 17, 2022 & December 31, 2022 issue of Science News.

Note that should you want to include additional questions and information about computer simulations in this discussion, check out the “Defining simulations” section of the lesson plan “The significance of simulations.”

Want to make it a virtual lesson? Post the online Science News article to your virtual classroom. Discuss the article and questions with your class on your virtual platform.

Population on a global scale

1. What does the graph included in the story show, according to the graph title? What is measured on the y-axis and x-axis? What are the units of measure and what increments are represented by each mark on the axes?

The graph shows the estimated global population from 1950–2100. The global population is measured in billions on the y-axis, and time is measured in years on the x-axis. As you move up the y-axis, the population increases in increments of 2 billion. On the x-axis, time is represented in increments of 10 years.

2. What do the colors of graphed lines represent? How was each line obtained, and why were the various lines included in the graph, according to the article? Choose a point on the line and describe the data it represents. Don’t forget to include appropriate units.

The dark gray line represents the observed global population from 1950 through 2021. These data are obtained from global population information gathered from previous years. The light gray lines represent global population projections. The projections are made by computer simulations and rely on many factors. The red line, which represents the median projection, is shown to summarize the different global population projections. From the graph, it appears that in 2000 there was a global population of about 6.1 billion people.

3. Use the graph to calculate the average rate of change per year from 2000 to 2020. Use the graph to calculate the median projected rate of change per year from 2060 to 2080.

From 2000 to 2020, the change is about 1.8 billion, or 0.09 billion per year. From 2060 to 2080, the median projected rate of change is about 0.4 billion, or 0.02 billion per year.

4. How would you describe the general trend in data that you see on the graph? How does the rate of change differ from observed to projected values?

There is a general upward trend in the global population until about 2080. The slope of the red line from 2022 to 2100 is not as steep as the line from 1950 to 2022, indicating that the growth rate might slow over time.

Extension: Think about different mathematical functions you know and use one in your description of the overall trend.

The overall shape of the graph looks like a natural logarithmic function.

5. Why do you think the graph is included in the article?

The graph is an easy way to show a reader the global population trend over time. It consolidates data collected by the United Nations into an easy-to-understand picture, as well as supports the claim that the world population has reached 8 billion and may peak around 10.4 billion in the 2080s. 

Processing projections

1. How do you think the United Nations calculated the observed global population?

The United Nations likely collected data on the number of people in different regions and countries, estimating to fill certain data gaps as needed, and adding it all up to find the sum.

2. What factors do you think went into creating the computer-simulated population projections? Brainstorm a list.

Some factors that were gathered for regions and countries were likely: life expectancy (perhaps influenced by several factors such as disease prevalence, poverty level, education rate, income), current population growth rate (probably determined by death rate and birth rate, and perhaps fertility rate), projected immigration and emigration rates, etc.

3. What happens to the range of the samples of projections as the dates go further into the future? Give specific data points to support your answer.

The range of population projections increases. In 2050, the projected population ranges from about 9.2 billion to about 10.1 billion, a difference of 0.9 billion. In 2100, the projected population ranges from about 8.5 billion to about 12.2 billion, a difference of about 3.7 billion.

4. How would you expect the uncertainty of the projections to change as the dates extend further into the future?

Predicted data becomes more uncertain as future years get further away from the current year. Each population projection builds on a predicted, uncertain value in the previous year.

5. Why do you think the United Nations found it worthwhile to project the global population? Why might it be beneficial to include many of the projections on the graph?

The global population projections can help inform future decisions about global issues. Including many projections in the graph sets out different possible scenarios to consider and emphasizes to the reader that there is uncertainty in the projected data.