Population and demographic trends underlie many environmental conditions. Some aspects of population and demographics, such as size and distribution, are major factors in land-use changes, energy and materials consumption, water use and water quality, waste generation, and development activities (for example, roads, buildings, marinas, reservoirs).

Population density and location is also linked to potential human exposure to unsafe concentrations of pollutants, possible increased risks associated with natural hazards such as floods, hurricanes, and tornadoes, and certain environmental equity issues. Expanding populations and urban sprawl contribute to loss of prime farmland, wetlands, and other habitats and to reduction in natural biodiversity and other environmental amenities such as wild and scenic areas. Population migration can exacerbate many of these changes. For example, population growth in the southwest has led to growth in energy use for air conditioning and water use for lawn irrigation.

The aging of the U.S. population also impacts environmental quality through increased migration to areas with many amenities and a moderate climate, greater utilization of parks and recreation areas, and growth in recreational or second home buying. Conversely, the aging population is more susceptible to air pollutants and other toxics.

The relationship between per capita income growth and patterns of environmental change, according to a World Bank study, suggests that some measures (waste generation, carbon emissions) continue to rise with increased per capita income while others (annual deforestation, dissolved oxygen in rivers, urban sanitation) tend to decrease. Other environmental implications of increased affluence include the growth in motor vehicle registration and travel, increased demand for new housing, and growth in household consumption of durable and non-durable goods (which drives a major proportion of industrial production).

This chapter examines key aspects of U.S. population growth, distribution, density, age-structure, and income distribution that underlie the environmental trends explored in later subject-area chapters.

TRENDS

U.S. Population Size and Growth Rate

The United States, with a mid-year 1998 population of 270 million people, ranks third in the world in population size behind China (1.239 billion people) and India (982 million people). The country’s population growth of 0.92 percent during 1998 was mostly the result of natural increase (births minus deaths). An estimated net gain from immigration of 854,000 people accounted for about one-third of the total annual increase in population (Figure 1.1).

The annual rate of population growth has changed significantly over the past 100 years. It was high in the first decade of the 20^th century (around 2.0 percent per year), declined during World War I and again during the Depression, and then increased after World War II during the Baby Boom Years, 1946 to 1964 (between 1.5 and 2.0 percent per year). The rate declined after 1965 to hover between 1.0 and 0.9 percent per year, increased slightly in the late 1980s and early 1990s, and has since decreased. The lower growth rate in the mid- to late- 1990s is the result of fewer births and greater number of deaths (Figure 1.2).

The changing age structure of the population is the principal reason for fewer births and more deaths. The changing age structure within the female population 15 to 44 years old (with more women entering the less-fertile childbearing ages) and declines in the age-specific fertility rates of Black women has led to fewer births. More deaths is attributed to the relatively high population growth rate among the oldest old (people 85 years and older) which has created a relatively larger population in age categories with greater susceptibility to death.

Current population growth is concentrated among the school-aged, Baby-Boom echo population (those 5 to 17 years), the middle-aged Baby-Boom population (those mid-30 to early-50 years), and the elderly (Figure 1.3). This differential increase in the elderly population is the result of improvements in life expectancy at advanced ages, high birth rates during the first decade of the 20^th century, and very high immigration from Europe during the early part of the 20^th century.

Over the course of the 20th century, the nation’s population has changed from primarily rural to primarily urban and suburban (Figure 1.4). Since 1950, suburban areas have grown dramatically, increasing from 35 million people (23 percent of the total population) to 135 million in 1998 (50 percent of the total). Rural population has shrunk from 66 million people in 1950 (44 percent of the total) to 54 million people in 1998 (20 percent of the total). Metropolitan growth between 1990 and 1998 was concentrated in the South and West, which together accounted for 82 percent of all metropolitan growth.

Population has increased in all regions of the country, but the rate of increase has been fastest in the West -- growing from 4 million to 60 million from 1900 to 1998 -- and the South -- growing from 24 million to 97 million over the same period (Figure 1.5). In terms of regional migration, the pattern is characterized by movement since 1960 from the Northeast and Midwest to the South and West.

In 1998, more than half of the U.S. population lived along the coast, an area that represents only one fourth of the U.S. land mass. As a consequence, areas of the coastal zone are densely populated, ranging from 422 people per square mile in 1998 along the Atlantic coast and 232 people per square mile in the coastal counties of the Great Lakes to 149.3 people per square mile along the Gulf coast and 71.6 people per square mile along the Pacific coast (Figure 1.6). In contrast, population density in the non-coastal portion of the United States was 48.1 people per square mile in 1998.

Over the past thirty years, the number of people living below the poverty line has fluctuated from a low of 23 million in 1973 (11 percent of the population) to a high of 39 million in 1993 (15 percent of the population). In 1998, the total was estimated at 34.5 million, or 12.7 percent of the population. The number of people in poverty declined for all races, pointing to the widespread benefits of a growing economy across the population. In 1998, the poverty rate was 10.5 percent for Whites, 26.1 percent for Blacks, and 25.6 percent for Hispanics (of any race). For the Asian and Pacific Islander population, the largest component of the remaining race groups, the poverty rate was 12.5 in 1998. Even though the poverty rate for Whites was lower than any other racial and ethnic groups, the majority of poor people (68 percent) in 1998 were White. In terms of residence, about 15 million poor people were living in central cities of metropolitan areas, 12 million in suburbs, and 7.5 million in rural areas (Figure 1.7).

References

Orians, Carlyn E. and Marina Skumanich, The Population-Environment Connection: What Does It Mean for Environmental Policy? (Batelle Seattle Research Center, Seattle, WA, 1997). (http://www.seattle.battelle.org/services/e&s/pop-env/index.htm)

U.S. Department of Commerce, Bureau of the Census, Historical Poverty Tables Based on the March Current Population Survey (http://www.census.gov/hhes/income/histinc/histpovtb.html)

--. Historical National Population Estimates: July 1, 1900 to July 1, 1999. (http://www.census.gov/population/estimates/nation/popclockest.txt)

--. Historical Statistics of the United States: Colonial Times to 1970, Part 1, Series A 30-37 (GPO, Washington, DC, 1975).

--. Metropolitan Area and Central City Population Estimates for July 1, 1999 and Revised April 1, 1990 Census Population Counts. Released in 2000. (http://www.census.gov/population/www/estimates/metropop.html)

--. Resident Population Estimates of the United States by Age and Sex: April 1, 1990 to July 1, 1999, with Short-Term Projection to November 1, 2000 (http://www.census.gov/population/www/estimates/nation2.html)

--. State Population Estimates and Demographic Components of Population Change: April 1, 1990 to July 1, 1999 (http://www.census.gov/population/www/estimates/statepop.html)

--. Statistical Abstract of the United States, 2000 (GPO, Washington, DC, 2000). (http://www.census.gov/prod/www/statistical-abstract-us.html)

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