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People and More People!

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The population of the world is more than 7.4 billion people.


Figure 1. Data source: U.S. Census Bureau

As I write (7/11/2017), the population of the world is 7,409,620,694. Actually, that’s a bit of a misrepresentation, for more than 2 people are added to the world every second, so even as I type the end of this sentence, the total is higher. By the time this post is published (10/5/2017), it will be 17.6 million higher.

Take a look at Figure 1 at right. It is a graph of world population over the history of civilization as estimated by the U.S. Census Bureau. It is one of those “hockey stick” graphs that scare environmentalists. For thousands of years the population of the world grew very slowly. Starting in the late 1600s or early 1700s, the rate of population growth began to quicken. The world population crossed 1 billion sometime just after 1800. It crossed 2 billion early in the 20th Century, 3 billion in 1959, 4 billion in 1974, 5 billion in 1987, 6 billion in 1999, and 7 billion in 2012.

That’s right, it took more than 11,000 years for the population to cross 1 billion, but in the following 200 years it grew by 6 billion. It took only 13 years for the last billion.

Figure 2. Data source: U.S. Census Bureau.

Figure 2 shows world population since 1950 in finer detail, and projects future population to 2050. In the chart, historical data is blue, projections are red. By mid-century, world population is projected to grow to 9.4 billion. The increase is remarkably consistent and relentless. If you look at the shape of the chart carefully, however, you can see a slight increase in the slope during the 1970s, and a slight flattening of the slope starting somewhere around 2025. The flattening is very slight, and world population is projected to increase by more than a billion in the 20 years from 2030-2050.

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Figure 3. Data source: U.S. Census Bureau

Figure 3 shows the growth in world population since 1950 and projected to 2050. The blue line shows the number of people added each year, and it should be read against the left vertical axis. The red line shows the percentage growth rate each year, and should be read against the right vertical axis. Both lines peak and then decline. In terms of the number of people added each year, the peak came in 1988, when 87.3 million persons were added to the world. Since then, it has declined, though only very moderately, and 77.6 million persons were added in 2016. Percentage growth in population peaked in 1966, when world population grew by 2.2%. It has declined since then, and in 2016 the world added 1.1% to its population.

Demographers project that the decline in both trends will continue, and by 2050, world population will grow by 42.9 million persons each year, or 0.46%. While that is a 45% decline from the number added in 2016, it is still more than the population of even the most populated state in the USA (California) and more than 7 times the population of Missouri in 2010.

Figure 4. Data source: U.S. Census Bureau.

Figure 4 shows similar data for the United States. The data starts in 1790, the year the first national census was conducted. The blue line represents the population of the country, and should be read against the left vertical axis. The red line represents the growth rate, and should be read against the right vertical axis. The blue line curves upward – as the population grew, more people were available to reproduce, adding a larger number of people with each decade. In 2010 the population was estimated to be 309 million. The rate of growth has slowed however. When the country was small, even a little bit of immigration added a significant fraction to the population. After the country had grown, even though more people were being added, they represented a smaller fraction. In 2010 the population of the USA grew by 0.83%, but the number of people added was 27.2 million, the second largest for any decade (1990-2000 was the largest at 33.5 million). Think of it: though the percentage growth is small, in terms of people, we’re adding a state the size of Texas every 10 years!

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Figure 5. Data source: U.S. Census Bureau

Figure 5 shows similar data for Missouri. Missouri first became a territory in 1810, so the chart begins with that year. Population is shown in blue, and should be read against the left vertical axis. The population growth rate is shown in red, and should be read against the right vertical axis. The population line for Missouri has a hump in it; the state grew very quickly during the mid-to-late 1800s. It has grown more slowly since then, and the population was about 6 million in 2010. For the same reasons as with the USA as a whole, the population growth rate was very fast when the state was small, but has slowed greatly, and in 2010 was 0.59%.

I will discuss some of what this data means in the next two posts.

Sources:

For current world population: U.S. Census Bureau. U.S. and World Population Clock. https://www.census.gov/popclock.

USA and Missouri data prior to 2000 are from U.S. Census Bureau. Part II. Population of the United States and Each State: 1790-1990. http://www.census.gov/population/www/censusdata/Population_PartII.xls.

USA and Missouri data for 2000 and later are from U.S. Census Bureau, Population Division. Table 1. Intercensal Estimates of the Resident Population for the United States, Regions, States, and Puerto Rico: April 1, 2000 to July 1 2010 (ST-ESTOOINT-01). http://www.census.gov/popest/data/intercensal/national/nat2010.html.

World population data are from: U.S. Census Bureau. World Population: Historical Estimates of World Population. https://www.census.gov/population/international/data/worldpop/table_history.php.

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