Us Demographic Trends and Its Environmental Impact

The United States, the third most populous country globally, accounts for about 4.5% of the world’s population. The U.S. population, currently estimated at 308.7 million persons, has more than doubled since its 1950 level of 152.3 million. More than just being double in size, the population has become qualitatively different from what it was in 1950. As noted by the Population Reference Bureau, “The U.S. is getting bigger, older, and more diverse.” The objective of this report is to highlight some of the demographic changes that have already occurred since 1950 and to illustrate how these and future trends will reshape the nation in the decades to come through 2050.
The Census Bureau projects that the U.S. population will continue to grow, to almost 440 million persons by year 2050, albeit at a slower pace than the growth recorded over the past half-century. More pessimistic growth projections are offered by the United Nations and the Social Security Administration, which estimate that the U.S. population will be 404 million or 411 million respectively in the same year.
The Census Bureau assumes that the growth rate will remain positive through year 2050, but will fluctuate over the time period. The current level of 0.8% per year will increase through 2030 to closer to 0.9% per year. After 2030 the growth rate is expected to return to 0.8%.
The Census Bureau uses demographic projection techniques to predict future trends in American fertility. They project that the total fertility rate will remain at or above replacement level, 2.1 births per woman age 15-44, through 2050. This is in contrast to much of Europe and to Canada, where fertility rates are below replacement level and not expected to increase. The Census Bureau suggest that these falling fertility rates are a result of societal changes, such as the increasing costs of raising a child, rising levels of women’s labor force participation, and delayed childbearing. While the U.S. has experienced these same societal changes, U.S. fertility remains higher because of societal adaptations such as increased access to child care and increased male involvement in household labor and childrearing
The U.S. Census Bureau projects that net migration will continue to be an important component of population growth in the United States through 2050 with net immigration continuing at higher rates than currently observed. Both gross immigration and gross emigration are important to consider when examining how immigration effects population growth and change. In general, the balance of gross immigration has exceeded gross emigration over the past century.
Using indirect demographic techniques, the Census Bureau estimated that the number of emigrants leaving the United States has been increasing over the past decades, reaching about 234,000 persons annually during the 1990s and increasing steadily through the first decade of the 21st Century. The Population Reference Bureau estimates almost 330,000 emigrants in 2009.
One of the most important demographic characteristics of a population is its age and sex structure. In general, a young population structure is seen in countries experiencing high fertility and rapid population growth, and the relevant policy considerations are whether there are sufficient schools and, later, enough jobs and housing to accommodate them. On the other hand, critical policy challenges in countries with old population structures are to develop retirement and health systems to serve the older population, often with simultaneous reductions in the number of working-age persons to support them. The population of the United States had been relatively young in the first half of the 20th century, a consequence of relatively high fertility, declining infant and childhood mortality, and high rates of net immigration to the United States by young workers and families. Since 1950, the United States has been in the midst of a profound demographic change: rapid population aging, a phenomenon that is replacing the earlier young age-sex structure with that of an older population. One in five persons in 2050 will be aged 65 or older.
The U.S. population is becoming more racially and ethnically diverse. This reflects two forces. First, immigration has been a major influence on both the size and the age structure of the U.S. population. Although most immigrants tend to be in their young adult ages, when people are most likely and willing to assume the risks of moving to a new country, U.S. immigration policy has also favored the entry of parents and other family members of these young immigrants. Second, major racial and ethnic groups are aging at different rates, depending upon fertility, mortality, and immigration within these groups.
The U.S. Census Bureau suggested that the environmental impact of a population can be expressed by the formula: I = P x A x T. The IPAT formula identifies three key factors in determining the impact of a population on the environment; the number of people, the amount each of them consumes, and the impact on the environment of creating each unit of consumption.
The formula most closely represents the situation where an environmental impact flows directly from consumption, for example, in identifying the greenhouse gas emissions associated with electricity use. There are a number of key projected demographic trends, a gradual increase in the number of people in the US; a faster increase in the number of older people; an increase in the average age of the population as people live longer; and a faster increase in the number of households, in particular the number of one-person households.
The pattern of demographic change will not be uniform; some areas will grow faster than others, and conversely some areas will see depopulation. A focus on total population alone may miss the differential effects arising from different consumption patterns of people of different ages, or in households of different sizes, and the different implications of population growth in one part of the country as opposed to another. A focus on average levels of consumption may also obscure differences in lifestyle. Different people will consume more or less according to their personal circumstances, their individual affluence, where they live, the stage of their life and their personal priorities. Despite this, the IPAT formula does provide a framework for thinking about the relationship between environmental impacts and demographic change.
Demographic change can influence waste production. For example, public attitudes and consumption practices can determine how much of a product is wasted, and changes in economic growth can influence the purchasing of products and, therefore, the amount and type of waste produced. Moreover, the link between consumption and waste generation is a complicated one, since, in terms of a product life cycle, waste is generated in the extraction, exploitation and production phases and not just in the consumption of the final product. Much of the waste associated with consumption may in fact occur in other countries where primary production takes place. Equally, some recycled waste is sent overseas for processing, and this too can have environmental implications.
Analysis has shown there are clear links between population size and greenhouse gas emissions, though the relationship is not always simple. The evidence suggests that emissions per person depend on income, technology, demographic factors like household size, city size and population density in built-up areas, institutional and economic factors like the availability of public transport at reasonable cost and convenience, and a host of behavioral factors like people’s propensity to walk, bike, share a car, or drive solo to work. For example, the carbon dioxide per person emitted by passenger transport is lower in more densely populated cities.
Growth in population can affect air quality through increased emissions from transport, electricity generation using fossil fuels, industry, and food production. Reactions in the atmosphere can produce number of secondary pollutants, particularly the photochemical oxidant gas ozone. Over the last 40 years, population growth coupled with increased mobility and consumption of energy and consumer goods have all contributed to drive up emissions. In summary, changes in affluence, resulting in increased mobility, with the potential for an ageing population to use vehicles more frequently as a result, and consumption, have the potential to drive up the emissions of air pollutants. Population growth in areas with poor urban air quality will contribute to further deterioration without mitigation measures. But in these areas, those most exposed to poor air quality are actually less likely to own their own vehicle, and hence do not contribute to the problem but suffer the effects of the behavior of others.
The IPAT formula provides a helpful framework for thinking about the environmental impact of the US population, and focusing on the three key elements which determine that impact, the size of the population, together with other demographic characteristics such as the age profile and the number of households, the affluence of the population reflected in lifestyles and patterns of consumption, and the influence of technology, which in some cases may reflect tighter regulatory standards. In practice the situation is often more complex than can be represented by a simple equation, with many factors in play which mean that there is no simple, linear relationship between the environmental impact and any one of the three factors, and the factors themselves are interrelated. Moreover, the relative importance of the different factors will vary from place to place.
Regardless of what may happen in the future, the United States will become a more diverse country: The only question is how diverse. The assumptions underlying the Census report, as does any projection of the U.S. population, cause us to stop and think about the national demographic future.

Works Cited
"International Programs - U.S. Census Bureau." Census Bureau Homepage. N.p., n.d. Web.

Cited: "International Programs - U.S. Census Bureau." Census Bureau Homepage. N.p., n.d. Web.