5.1 Human population density varies significantly across Earth

5.1–5.3 Science

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(Jorg Hackemann/Shutterstock)

Human population density lies at the root of environmental damage. In order to minimize the environmental impact of human societies, we need to know where people live today and where they will be concentrated in the future.

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What might be the impacts on the environment of concentrating the population in densely populated cities versus spreading the population across the landscape?

population density The number of individuals in a population per unit area.

In Bangladesh, people are crowded together with an average density of nearly 1,000 people on every square kilometer of land (or 0.39 square miles). Australia, by comparison, has an average of just 3 people in the same-size area. Such regional contrasts provide a graphic demonstration of how human population density varies. Within countries, the highest population densities are generally found along coasts and river valleys. The lowest population densities occur mainly in extreme environments such as deserts and arctic tundra. The Ganges river delta in Bangladesh was historically a very advantageous place to settle because it could support a relatively high population density with its fertile soil and ample water, whereas Australia’s outback, in its recent history, has been better suited to kangaroos and lizards than to people (Figure 5.1).

HUMAN POPULATION DENSITIES VARY GREATLY ACROSS THE GLOBE
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FIGURE 5.1 Some environments typically support higher population densities compared with others, often depending on the local climate and natural resources like water, soil quality, and raw materials.
(© Patagonik Works/Alamy) (© Ton Koene/age fotostock)

immigration The movement of individuals into an area, or country, to which they are not native.

emigration The movement of individuals out of one area, or country, to another.

We know that people don’t always stay in the place where they were born. Population density results from a combination of the rates of birth, death, immigration (movement of individuals into a population from the outside), and emigration (movement of individuals away from a population to another area) (Figure 5.2). On a regional scale, in places where rates of birth and immigration exceed rates of emigration and death, population density will increase. In regions where birth and immigration rates are lower, population density declines.

POPULATION DENSITY: A DYNAMIC BALANCE BETWEEN OPPOSING PROCESSES
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FIGURE 5.2 Population density is the outcome of the interplay of immigration and births versus emigration and deaths.

Today, populations around the world are becoming increasingly concentrated in cities as people migrate from rural to urban areas. By 2014 over half the world’s population was living in cities, with that proportion expected to rise to two-thirds by 2050. However, in some countries the proportion of the population living in cities is already much higher. For example, in 2014, over 80% of the populations of the United States and Canada were urban, while in Japan and Belgium that proportion was over 90%. One of the consequences of this migration has been the formation of mega-cities with populations of more than 10 million (Table 5.1). The urban population of Earth will continue to grow, as rural to urban migration remains high through the middle of the century.

TABLE 5.1
THE 10 LARGEST MEGA-CITIES
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Think About It

  1. How do you explain the higher population densities in coastal areas around the world?

  2. Europe, Canada, and the United States are within about 10% of each other in terms of land area. However, their population densities differ markedly (Europe: 70 per km2; United States: 31 per km2; Canada: 3.2 per km2). What factors likely account for these differences?

  3. What factors are attracting people from rural areas to cities?