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Unit 5: Human Population Dynamics // Section 5: Population Growth and the Environment

Many people (including national leaders) worry that population growth depletes resources and can trigger social or economic catastrophe if it is not contained. As discussed in the preceding section, most of the projected population growth during this century will take place in developing nations. These countries have faced many challenges in recent decades, including low levels of education, poor health standards, poverty, scarce housing, natural resource depletion, wars, and economic and political domination by other countries. In Sub-Saharan Africa industrial development has stalled and most workers still make a living from subsistence agriculture.

Countries in this situation generally have devoted less energy to addressing environmental issues than their wealthier neighbors, so these problems have intensified. Especially in the poorest countries, therefore, future population growth is likely to make environmental deterioration worse (although it does not automatically follow that countries with low population growth rates will have cleaner environments).

However, the relationship between population and the environment is complex. As noted in section 1, human societies' impacts on the environment are a function of three major, interconnected elements: population size, affluence or consumption, and technology. An expanded version of the IPAT equation separates technology into two factors: resource-intensity (how many resources are used to produce each unit of consumption) and waste-intensity (how much waste each unit of consumption generates), and also considers the sensitivity of the environment (footnote 11).

Societies' environmental impacts take two major forms. First, we consume resources such as land, food, water, soils, and services from healthy ecosystems, such as water filtration through wetlands. (For more on ecosystem services, see Unit 9, "Biodiversity Decline.") Over-consumption uses up or severely depletes supplies of non-renewable resources, such as fossil fuels, and depletes renewable resources such as fisheries and forests if we use them up faster than they can replenish themselves (Fig. 11).

Land conversion for grazing in the Amazon rainforest

Figure 11. Land conversion for grazing in the Amazon rainforest
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Source: Courtesy National Aeronautics and Space Administration, Goddard Space Flight Center.

Second, we emit wastes as a product of our consumption activities, including air and water pollutants, toxic materials, greenhouse gases, and excess nutrients. Some wastes, such as untreated sewage and many pollutants, threaten human health. Others disrupt natural ecosystem functions: for example, excess nitrogen in water supplies causes algal blooms that deplete oxygen and kill fish. (For more on these pollutants, see Unit 8, "Water Resources"; Unit 10, "Energy Challenges"; Unit 11, "Atmospheric Pollution"; and Unit 12, "Earth's Changing Climate.")

Rising population growth rates in the 1950s spurred worries that developing countries could deplete their food supplies. Starting with India in 1951, dozens of countries launched family planning programs with support from international organizations and western governments. As shown above in Figure 4, total fertility rates in developing countries declined from six children per woman to three between 1950 and 2000. National programs were particularly effective in Asia, which accounted for roughly 80 percent of global fertility decline from the 1950s through 2000 (footnote 12). It is important to note, however, that this conclusion is controversial. Some researchers have argued that desired fertility falls as incomes grow—and that family planning has essentially no independent influence (footnote 13).

These programs sought to speed the demographic transition by convincing citizens that having large numbers of children was bad for the nation and for individual families. Generally they focused on educating married couples about birth control and distributing contraceptives, but some programs took more coercive approaches. China imposed a limit of one child per family in 1979, with two children allowed in special cases (Fig. 12).

Poster advertising China's one-child policy, 1980s

Figure 12. Poster advertising China's one-child policy, 1980s
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Source: Artist Zhou Yuwei. Courtesy of the International Institute of Social History Stefan R. Landsberger Collection,

In some parts of China the one-child policy reportedly has been enforced through methods including forced abortions and sterilizations. Forced sterilizations also occurred in India in the 1970s. These policies have spurred some Indian and Chinese families to practice selective abortion and infanticide of female babies, since boys are more valued culturally and as workers. Population sex ratios in both countries are skewed as a result. In 2005 there were 107.5 males per 100 females in India and 106.8 males per 100 females in China, compared to a worldwide average of 101.6 males per 100 females. Females slightly outnumber males on every continent other than Asia (footnote 14).

Large societies consume more resources than small ones, but consumption patterns and technology choices may account for more environmental harms than sheer numbers of people. The U.S. population is about one-fourth as large as that of China or India, but the United States currently uses far more energy because Americans are more affluent and use their wealth to buy energy-intensive goods like cars and electronics. But China and India are growing and becoming more affluent, so their environmental impacts will increase because of both population size and consumption levels in the next several decades. For example, in 2006 China surpassed the United States as the world's largest emitter of carbon dioxide (CO2), the main greenhouse gas produced as a result of human activities (footnote 15).

Economies tend to become more high-polluting during early stages of economic development because they first adapt inexpensive technologies that are relatively inefficient—for example, simple manufacturing systems and basic consumer goods such as cars. As income rises and technologies diffuse through society, consumers start to value environmental quality more highly and become more able to pay for it.

Some analysts have argued that developing countries can skip the early stage of industrialization through "leapfrogging"—deploying advanced, clean technologies as soon as they are fielded in developed nations, or even earlier. For example, some developing countries have skipped past installing telephone poles and wires and moved straight to cell phones as a primary communication system. If fast-growing nations like China and India can leapfrog to clean technologies, they can reduce the environmental impacts of their large and growing populations (Fig. 13). However, many new technologies will not flow easily across borders in the absence of special efforts. Developed countries and international financial institutions can promote technology transfer to reduce the environmental impacts of growth in developing countries.

Youths installing solar panels to power a rural computer center, São João, Brazil

Figure 13. Youths installing solar panels to power a rural computer center, São João, Brazil
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Source: Courtesy United States Agency for International Development.

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