Following the publication of Aldo Leopold’s “A Sand County Almanac” in 1949, Rachel Carson’s “Silent Spring” in 1962 and Paul and Anne Ehrlich’s “The Population Bomb” in 1968, the early 1970s were a time of rapidly expanding consciousness of issues associated with environmental degradation and human responsibility for those impacts on the environment. In 1969 the Cuyahoga River in Cleveland, Ohio, actually caught on fire, and there was a significant oil spill in the Santa Barbara channel. These events likely contributed to precipitating the first Earth Day celebration in 1970. Approximately one year after the first Earth Day celebration, Paul Ehrlich and John Holdren published an important conceptual paper titled “Impact of Population Growth.” This paper postulated an oft-cited equation: I = P × A × T (where “I” is Impact, “P” is Population, “A” is Affluence and “T” is Technology).
Questions about human impact on the environment remain with us today and are perhaps even more pressing in light of global climate change, peak oil and the rapid loss of biodiversity. These questions are often framed within the broader context of “Sustainability.” In a strictly biophysical sense, “sustainability” is perhaps a more palatable way of expressing the idea of “Carrying Capacity.” The carrying capacity of the earth is the number of human beings that can be sustained indefinitely by the earth’s natural endowment.
The Global Footprint Network is a nongovernmental organization (NGO) that is interested in promoting sustainability by educating the public and national governments with scientific evidence regarding ideas of carrying capacity, ecological sustainability and improving human well-being. The Global Footprint Network has developed a metric called “The Ecological Footprint” that contrasts a multivariate measure of human impact on the planet (the ecological footprint) with a multivariate measure of the earth’s natural endowment (biocapacity). Here we explore a simple, objective and independent measure of something akin to their ecological footprint metric. This measure is: (1) global in scope yet spatially explicit so as to be able to be disaggregated to national and subnational levels; (2) derived from measurements that cannot be corrupted or manipulated by government agencies; (3) is mappable and monetizable (i.e., a dollar value to be assigned at the national level to both ecological surpluses and ecological deficits) and (4) correlates strongly with the Global Footprint Network’s National Footprint Account measures. We do this using global datasets derived from satellite imagery. Our measure of “Human Impact” will be pavement or “Impervious Surface Area,” and our measure of “Biocapacity” will be Net Primary Productivity from Photosynthesis or “NPP.”
This explores several questions related to sustainability and carrying capacity by mapping and monetizing both human “Impact” on the earth; and mapping and monetizing the earth’s “ecosystem services” or “natural endowment” as measured by photosynthesis (aka, Net Primary Productivity or NPP). We use these maps to determine which countries are beyond their carrying capacity (the “real debtor nations”) and which countries are below their carrying capacity (the “real surplus nations”). In addition, we calculate a dollar value of these national “debts” and “surpluses.”
The term “Sustainable Development” was first put forth in 1983 by the World Commission on Environment and Development (WCED). The chair of this commission was a woman named Gro Harlem Brundtland whose minor accomplishments include serving three times as the Prime Minister of Norway and as Director General of the World Health Organization. The Brundtland Report coined the notion that “Sustainable Development is development that meets the needs of the present generation without compromising the ability of future generations to meet their own needs.” Many would argue that this idea of “sustainability” is brilliantly vague, while others would argue that this ambiguity makes it practically useless.
Here we explore the idea of “sustainability” using global maps of photosynthesis and impervious surface and a Geographic Information System (GIS). The earth provides many ecosystem services or “benefits” that enable and enhance human existence. Humanity, in turn, imposes myriad environmental impacts or “costs” on the earth. We explore the idea of mapping these costs and benefits using proxy measures. We set the total value of the world’s ecosystem services to be equal to the total cost of anthropogenic environmental impacts at $50 trillion (roughly the global GDP in the year 2000). A global representation of ecosystem service value is mapped at one kilometer squared resolution using Net Primary Productivity (NPP) as a proxy measure of ecosystem service value (Figure 1). A similar global representation of environmental impact is mapped using pavement (i.e., anthropogenically created impervious surface area or ISA) as a proxy measure of cost (Figure 2). Subtracting the 50 trillion mapped onto ISA from the 50 trillion mapped onto NPP produces a one kilometer squared resolution map of those areas where (1) human-imposed costs exceed naturally supplied benefits, resulting in an ecological deficit; (2) human costs balance with environmental benefits and (3) environmental benefits exceed human costs, resulting in an ecological surplus. Mapping this ecological balance produces a spatially explicit and monetized representation of sustainability that can be aggregated to national levels (Figure 3). Table 1 lists the 20 countries with the largest ecological surplus. Table 2 lists the 20 largest “debtor nations” according to this accounting framework. A potential benefit of this approach to mapping and monetizing sustainability is the idea that the national values derived from this difference map suggest a starting point for discussions of the dollar values and costs of both sustainable and nonsustainable behavior on the part of the nations of the world.
References and further reading
Ehrlich, Paul R. and John P. Holdren. 1971. “Impact of Population Growth.” “Science” 171: 1212–17.
World Commission on Environment and Development. “Our Common Future.” 1987. Oxford: Oxford University Press.
Wackernagel, M. and Rees, W. 1996. “Our Ecological Footprint: Reducing Human Impact on the Earth.” Gabriola Island, B.C., Canada: New Society Publishers.
Costanza, R. et al. 1997. “The Value of the World’s Ecosystem Services and Natural Capital.” “Nature,” vol. 387.
Daily, Gretchen, ed. 1997. “Nature’s Services: Societal Dependence on Natural Ecosystems.” Island Press.
Thom Hartmann. 2004. “The Last Hours of Ancient Sunlight.” Broadway Press.
Elvidge, Christopher Elvidge, et al. 2007. “Global Distribution and Density of Constructed Impervious Surfaces.” “Sensors,” 7, pp. 1962–79.
Imhoff, Marc L., et al. 2004. “Global Patterns in Human Consumption of Net Primary Production.” “Nature,” 429: 870–73.
Sutton, Paul C., et al. 2009. “Paving the Planet: Impervious Surface as a Proxy Measure of the Human Ecological Footprint Progress.” “Physical Geography,” 33(4), pp. 1–18.
Sutton, Paul, et al. 2011. “The Real Wealth of Nations: Mapping and Monetizing the Human Ecological Footprint.” “Ecological Indicators,” DOI: 10.1016/j.ecolind.2011.03.008.
The figures, tables and text in this article are adapted from a previously published journal article.