05 May 2014

President’s Commentary: How Many People Are Enough (Too Many)?

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*President’s Commentary: How Many People Are Enough (Too Many)?
by Bob Hughes

In the five minutes that you take to read this commentary, approximately 1,000 new human babies will be added to Earth’s current 7.2 billion people. From the evolution of Homo sapiens, we did not reach our first billion until 1804, doubling again in 1930 to 2 billion, and again to 4 billion in 1974. At current population growth rates (around 1.2% per year) or about 300,000 per day, global population will double again to 8 billion in 2024 (www.worldometers.info/world-population), a level many feel far exceeds Earth’s carrying capacity (Pengra 2012). As biologists, we know that such growth rates cannot persist. Those of us who think ecologically, see the effects of population growth multiplied by per capita resource consumption manifested in increased listings of threatened and endangered species (Figure 1), climate change, climate chaos, degraded ecosystem services (including water quality and availability, fisheries, and coral reef condition; Millennium Ecosystem Assessment 2005; Pengra 2012). Such global changes indicate that Earth’s carrying capacity has already been exceeded (Pengra 2012). With the USA being the third most populous nation in the world and having an excessive ecological footprint (Ewing et al. 2010), it is important for us to stem our own population growth to demonstrate our concern with the issue. But four socioeconomic factors hinder progressive actions to attaining zero or negative population growth in the USA.

1) Population growth is a component of economic growth, determining its natural rate (Harrod 1939). In addition, neoclassical economists regard population growth as necessary for per capita growth in gross domestic product (GDP) over the long term (Romer 1990; Jones 1998). That is, neoclassical economists believe more people are needed to stimulate more consumption per person. And economics, regardless of the general ignorance of its practitioners in the laws of physics and ecology, has greater influence in governments than the natural sciences. Likewise, governments and the media pay greater attention to short-term economic indicators than multiple indicators of ecological status and trends that are reported with lower frequencies and have far greater long-term implications for Earth’s biota (e.g. Stocker et al. 2013; USEPA 2009; 2013).

2) The USA has a fairly open and weakly enforced immigration policy. In the USA, the mean total fertility rate (births per woman) was 2.06 in 2013 (www.cia.gov/library/publications/the-world-factbook/rankorder/2127rank.html; accessed December 2013). Without immigrants, the USA total fertility rate would be 2.05 because 80% of births are to native mothers. However, legal and illegal immigrant mothers tend to have more children in the USA than in their native countries, 2.6 and 3.1, respectively (Camarota 2005). Likewise, native mothers have more children in the USA than in 124 other nations. Nonetheless, legal and illegal immigrants add about 2.3 million persons to the USA population annually, accounting for much of the USA population growth. Without those additions, the USA population would stabilize in the long run (Camarota 2005; Hurlbert 2011). Thus resolving the human overpopulation problem in the USA must incorporate immigration policy as well as birth rates.

3) Reproductive rights are considered an inviolable human and religious right, regardless of family size or ecological or sociological impact. But because of the massive ecological footprint of each USA resident as well as the value of human life, one can make ethical arguments in favor of government support for family planning, health care, and greater economic and educational opportunities for women and the poor (Abernethy 1993; Limburg et al. 2011). Nonetheless, there is ample evidence that increased economic opportunity alone, or the perception thereof, stimulates population growth (Abernethy 1994; Camarota 2005).

4) Federal and state governments subsidize children through tax exemptions for dependent children, regardless of number, and cash assistance for needy families. It is unlikely that many parents choose to have children because of tax exemptions or cash payments. However, nearly 4 million births per year in the USA (www.cdc.gov/nchs/fastats/births.htm) and a $3,900 tax exemption per child (for 2013) would equate to $15.6 million for newborns alone, assuming those parents have sufficient taxable income. Regarding families lacking sufficient income, the USA spent over $16 billion per year (2006-2013) in Temporary Assistance for Needy Families, typically families with one unemployed parent and one or two children (www.fas.org/sgp/crs/misc/RL32760.pdf). If subsidies to parents are deemed warranted for having children, why not tax credits or payments for childlessness, or a limit of one exemption? Such policies would recognize an overpopulated world and nation as well as persons who elect childlessness or a single child for ecological, sociological or ethical reasons.


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Camarota, S. 2005. Birth rates among immigrants in America: comparing fertility in the U.S. and home countries. Center for Immigration Studies. (www.cis.org/ImmigrantBirthRates-FertilityUS; accessed December 2013).

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Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (editors). 2013. Summary for policymakers. In: Climate change 2013: the physical science basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, New York, New York. www.climatechange2013.org/images/uploads/WGI_AR5_SPM_brochure.pdf (accessed December 2013).

USEPA (U.S. Environmental Protection Agency). 2009. National lakes assessment: a collaborative survey of the Nation’s lakes. EPA 841-R-09-001. Office of Water and Office of Research and Development, Washington, DC

USEPA (U.S. Environmental Protection Agency). 2013. National rivers and streams assessment 2008-2009: a collaborative survey. EPA/841/D-13/001. Office of Wetlands, Oceans and Watersheds and Office of Research and Development, Washington, DC

Figure 1. Number of threatened and endangered species as a function of population size in the USA (adapted from Limburg et al. 2011).


*This is a corrected version.