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-Sahara Africa industrial development has stalled and most errors 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 n the environment are a function of three major, interconnected elements: population size, affluence or consumption, and technology. An expanded version of the PAT 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). Figure 1 1.
Land conversion for grazing in the Amazon rainforest’s See larger Image 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 asses, 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 asses spurred worries that developing countries could deplete their food supplies. Starting with India in 1 951, dozens of countries launched Emily 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 asses through 2000 (footnote 12). It is important to note, however, that this conclusion is controversial.