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Decoupling and Ecological Sustainability

Module by: Steven Hinson. E-mail the author

Summary: This module summarizes the issue of ecological sustainability with respect to human population and economic growth. It explains the concept of overshooting, introduces the I-PAT equation, and uses numeric examples to introduce the issues surrounding sustainable economic growth.

Ecological Overshooting

In 1944, the US Coast Guard released 29 reindeer on St Matthew Island in the Baring Sea. The island, roughly the size of a mid-sized city, was largely devoid of fauna and had no inhabitants outside of the personnel assigned to the Coast Guard’s Loren Station. Shortly after the release, the station and the herd were abandoned.

Over the next twenty years, David Klein, a researcher at the University of Alaska, visited the island three times to assess the condition of the herd. On his first visit in 1957 he observed that, in the absence of predators and with plentiful food, the size of the herd had increased from the original 29 to 1,350. On his subsequent visit in 1963, the herd had increased to an estimated 6,000 animals. However on this second visit, he also noted apparent overconsumption of the vegetation and the declining weights of the deer. When he was finally able to return again in 1966, the population had collapsed due to starvation and only 42 deer remained. (Klein, 1968)

The example of the reindeer on St Matthew Island is frequently cited as an example of ‘overshooting’. Rather than increase to a sustainable level, unchecked, animal populations have a tendency to over-populate and as a result over-consume the available food supply. The result is an indefinite cycle of recovery, collapse, and recovery. This example often accompanies the assertion that the human population likewise occupies a planet of finite resource and ecological abundance and is therefore subject to the same risk. In 1972, the Club of Rome issued a report that argued rapid population growth and resource depletion would lead to a population collapse during the 21st century. (Meadows, 1974)

To understand their alarm, consider Table 1. From the year 1000 to the year 1800, world population increased roughly 3.5 times. From 1800 to the year 2000, a span one fourth as long, the population increased 7 times. But even more importantly, consider the third column. World Per Capita Real Gross Domestic Product (PCRGDP) is a rough estimate of the level of economic activity of the average person. Throughout human history until roughly 1800, this number had remained more or less constant. And so the impact of human beings on their environment was limited to population growth. But beginning in the late 18th century, per capita consumption began to increase at an increasing rate. Between 1800 and 2000, the average human being increased her consumption 33.5 times. The fourth column is the product of columns two and three. And so it provides a measure of the combined effect of population and consumption increases. For the eight hundred years beginning in 1000 A.D., the activity of human beings increased 5 times. Over the next two hundred years, the increase was 234 times!

Table 1

Year

Pop (M)

PCRGDP '90$RGDP '90$

1000 265 133 35,245
1100 320 124 39,680
1200 360 104 37,440
1300 360 89 32,040
1400 350 128 44,800
1500 425 138 58,650
1600 545 141 76,845
1700 610 164 100,040
1800 900 195 175,500
1900 1,625 679 1,103,375
2000 6,272 6,539 41,012,608

So is the human population, like the reindeer on St Matthew Island, facing inevitable (if not imminent) collapse? There is evidence that human activity has led us to the point of ecological overshoot. Ewing, Moore, Goldfinger, Oursler, Reed, & Wackernagel (2010) report that while the Earth had the biocapacity in 2007 to provide 4.4 acres per person of ecological services to the then population of 6.7 billion persons, the actual consumption was 6.7 acres per person. In other words, the Earth needed to be roughly half-again as large as it was in order to sustainably support the 2007 level of human activity (i.e. without overshooting).

But then predictions of population collapse aren’t without precedent. The Reverend Thomas Malthus (1798) likewise predicted the collapse of the English population. Diminishing returns to cultivation, he argued, guaranteed at best geometric expansion of the food supply. Population on the other hand, temporarily freed from malnourishment, would instead grow exponentially - an assertion Table 1 supports. And so, it was inevitable that the demands of population would exceed the availability of food resulting in subsequent starvation and decrease in the standard of living for most of the remaining population to mere subsistence.

What Malthus inadequately allowed for though were advances in the technology of agriculture. The increased utilization of first natural and then synthetic fertilizers overwhelmed the effects of diminishing returns to agricultural expansion and yields continued to increase at a rate in excess of population growth (at least within the industrialized nations.)

Ehrlich (I-PAT) Equation

So the important question is whether future technological innovation will allow for both anticipated population growth and continuing improvements in the standard of living of the world’s population. To formalize the underlying relationship between the relevant variables, the Ehrlich equation (Ehrlich, 1973) is frequently utilized:

I = P x A x T

‘I’ represents the overall ecological impact of human activity. Depending on the question at hand, this might be measured in any one of multiple ways. If one is interested in oil consumption, it might be measured in barrels extracted. Where if instead, you’re interested in global warming, you might measure CO2 emissions.

‘P’ represents the world population and ‘A’ measures the average level of affluence (often measured by Per Capita RGDP.) Finally, ‘T’ represents the current state of technology such that if ‘I’, for example, measures total ecological footprint1 (measured in acres) then T would represent the amount of acreage utilized per dollar of RGDP. Consequently, improvements in technology result in a decrease in T.

Consider the following data from Ewing et al (2010). In 2007, the world population was 6.7 billion persons. Per Capita RGDP (our measure of affluence) was approximately $7,400 per person. And T was 0.0009 acres per one dollar of RGDP. So: I = 6.7B x$7,400 x 0.0009

Or I = 44.7 Billion Acres

So in 2007, we collectively utilized the equivalent of 44.7 billion acres of ecological services (as compared to a ‘sustainable maximum’ of approximately 29.3 billion acres.)

Decoupling

So back to the question whether innovation can reduce T, and, if so, can it do so sufficiently to prevent ecological collapse? In figure 2, energy use, measured in kilograms of oil equivalent, is utilized as a measure of ‘I’. Over the 28 years represented, per capita RGDP increased 10 times while per capita energy use increased only 1.3 times. Based on this we can say that technology has clearly led to a ‘decoupling’ of energy use from economic growth.

But it’s important to note that while ‘relative’ energy use has declined, ‘absolute’ use has continued to increase with RGDP. To see this, consider Table 2 below. In 1971 it took 1.58 kilograms of ‘oil equivalent energy use’ to produce one dollar of RGDP. By 2009, technology change had reduced this to only one-fifth a kilogram per dollar of RGDP (an 87% reduction.)2

Table 2
1971 2009
I (kg oil use equivalent) 5,032,712.46 12,192,064.68
= Population (m) 3,762.60 6,763.70
x Affluence ($) 849.03 8,588.28 x Technology (kg/$) 1.58 0.21

However, the combined effect of population and economic growth more than offset the reduction in ‘T’ and so ‘I’, total energy use, actually more than doubled over this time period. So when discussing decoupling we must make a distinction between ‘relative decoupling’ as demonstrated here and ‘absolute decoupling’. If impact decoupling had occurred, ‘I’ would have remained constant (or ideally decreased) even as population and affluence increased.

So, how much greater an improvement in ‘T’ would have been required to achieve absolute decoupling? The 2009 value of ‘T’ would have to have been 0.087 to leave ‘I’ unchanged. Or in percentage terms, energy use per dollar would have needed to decrease by 95%.

Plausibility

While at face value the difference in an 87% reduction in energy intensity and a 95% reduction seems modest, the magnitude might be quite significant. Reductions in ‘T’ like all other productive processes are subject to the ‘Law of Diminishing Returns’. Initial reductions in ‘T’ result from the lowest hanging fruit allowing for somewhat dramatic initial decreases. Further reductions are more difficult and therefore, in absolute terms, tend to be smaller in magnitude.

Figure 3 is an actual plot of the computed value of energy use per dollar of RGDP for each year beginning in 1971 and ending in 2009. As expected, the early 1970s saw significant reductions in energy intensity. But during the 1980s, the declines were smaller, and by the 1990s the graph appears nearly flat. Of course this is intuitive. Consider the implications of a linear decreasing relationship. Given sufficient time (and corresponding innovation), the line would cross the horizontal axis. ‘T’ would be zero implying we could produce goods, heat and cool our homes, and drive our cars without expending any energy whatsoever.

So the answer appears to be that reductions in ‘T’ simply buy us time. Just how much time is a subject of some disagreement. But it is inconceivable that ‘T’ could ever reach zero across all resources and ecological services provided by a finite Earth. So, barring corresponding reductions in population and/or affluence, the Reverend Malthus will eventually be proved right.

References

Delong, B. (1998, May 24). Estimating World GDP, One Million B.C. – Present. Retrieved April 17, 2012 from http://www.j-bradford-delong.net/TCEH/1998_Draft/World_GDP/Estimating_World_GDP.html

Economic Research Service of USDA (2012). International Macroeconomic Data Set. Washington, DC. Retrieved March 26, 2012 from http://www.ers.usda.gov/data/macroeconomics

Ehrlich, P.R. & Holdren, J.P. (1971). Impact of Population Growth Science, Science, 171 (3977), 1212-1217

Ewing, B., Moore, D., Goldfinger, S., Oursler, A., Reed, A., & Wackernagel, M. (2010). The Ecological Footprint Atlas 2010. Oakland: Global Footprint Network.

Global Footprint Network (2010). National Footprint Accounts Data Set. Oakland, CA. Retrieved February 10, 2012 from http://www.footprintnetwork.org/en/index.php/GFN/page/ecological_footprint_atlas_2008/

Klein, D.R. (1968). The Introduction, Increase, and Crash of Reindeer on St. Matthew Island. The Journal of Wildlife Management, 32 (2). 350-367

Malthus, T. R. (1798) An Essay on the Principle of Population. Library of Economics and Liberty. Retrieved April 20, 2012 from the World Wide Web: http://www.econlib.org/library/Malthus/malPop1.html

Meadows, D.H., Meadows, D.L., Randers, J., & Behrens III, W. (1974). The Limits of Growth: A Report to the Club of Rome’s Project on the Predicament of Mankind. New York: Universe Books.

UNEP (2011). Decoupling natural resource use and environmental impacts from economic growth, A Report of the Working Group on Decoupling to the International Resource Panel. Fischer-Kowalski, M., Swilling, M., von Weizsäcker, E.U., Ren, Y., Moriguchi, Y., Crane, W., Krausman, F., Eisenmenger, N., Giljum, S., Hennicke, P., Romero Lankao, P., Siriban Manalang, A. Retrieved March 20, 2012 from http://www.unep.org/resourcepanel/Publications/Decoupling/tabid/56048/Default.aspx.

Wackernagel, M. & Rees, W. (1996). Our Ecological Footprint: Reducing Human Impact on the Earth. Gabriola Island, BC: New Society Publishers

World Bank (2012). Country Level Data Series. Washington, DC. Retrieved April 20, 2012 from http://data.worldbank.org/topic

Footnotes

1. Ecological footprint is a concept developed by Wackernagel and Rees (1996) that compares the computed carrying capacity of the Earth to the extraction of natural resources and the utilization of ecological services (e.g. as a carbon sink). For a complete overview, visit http://www.footprintnetwork.org

2. Computations by author using data from World Bank (2012) and Economic Research Service of the USDA (2012).

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