Many economists, and most physical scientists, assume that the relationship between economics and the second (entropy) law of thermodynamics concerns resource depletion and scarcity. In this belief they are, in a sense, disciples of the late Nicholas Georgescu-Roegen, who famously said: 'The entropy law is the taproot of economic scarcity' and many other words to that effect (Georgescu-Roegen 1971, 1977). As noted at the beginning of this chapter, the economy is a system that extracts low entropy resources from the environment and rejects high entropy wastes back into the environment. While solar energy was the original source of fossil fuels that accumulated in the earth's crust during the Carboniferous era, several hundred million years ago, we humans are dissipating those resources at a rate thousands or even millions of times faster than they were created.
An aspect of the depletion argument concerns recycling. One consequence of the second law is that recycling can never be 100 percent efficient. At first sight, this would imply that scarce materials like platinum must actually disappear from the surface of the earth, which is not the case. What is true is that as the quality of the resource base declines towards the average in the earth's crust, the amount of exergy required to extract and re-concentrate it increases to a maximum. In a finite planetary environment, the concentration of a scarce metal can never fall below the average. This means that recycling will become more difficult over time, but it will never become impossible (Mayumi 1993; Ayres 1998a, 1999).
The popular notion of perfect recycling in a 'circular economy' (by industrial analogs of decay organisms) with 'zero emissions' is off base in a real economy. Contrary to Georgescu-Roegen's assertions, perfect recycling is theoretically possible given a flow of exergy from outside the system (for example, from the sun).18 But zero emissions can be ruled out as a practical matter, if only because there is always a point at which the benefits of more complete waste treatment (or recycling) are less than the costs. This is the fundamental basis for benefit-cost analysis (for example, Herfindahl and Kneese 1973; Boadway 1974.) In fact, even the notion that natural ecosystems are perfect recyclers is quite false. The biosphere recycles carbon, oxygen and nitrogen with fairly high efficiency. Yet lignite, coal, petroleum and natural gas are actually transformed biological wastes.19 Other elements needed by living systems are not recycled biologically to any significant degree, including phosphorus, sulfur, potassium calcium and iron. Chalk, limestone, iron ores and phosphate rock are all accumulations of biological wastes. The fact that they are sufficiently concentrated to be extracted economically as 'ores' is very fortunate for us, but somewhat irrelevant to the question of recycling. The ways in which materials are extracted, transformed and used in the real industrial economy, and the environmental implications, are the substance of the new field of Industrial Ecology.
The idea that economic growth must be limited by physical resource scarcity actually has quite a long history. It goes back, at least, to Thomas
Malthus, who saw arable land as the limiting factor (Malthus 1946 ). Jevons in the 19th century worried about future availability of energy from coal (Jevons 1974 ). Since 1919, there has been a series of predictions that petroleum reserves are about to run out, each 'crisis' followed by new discoveries and another glut (Yergin 1991). Scarcity worries were behind the neo-Malthusian 'limits to growth' thesis, propounded in the 1970s by the Club of Rome (Meadows et al. 1972). However, an authoritative study published by Resources for the Future Inc. had strongly indicated that scarcity - as indicated by price, production and reserve trends - was not yet a problem for any exhaustible mineral resource (Barnett and Morse 1963). A follow-up in 1979 seemed to confirm that result (Barnett 1979). This optimism might now have to be modified, at least with respect to oil and natural gas (Campbell and Laherrere 1998; Campbell 2004; Deffeyes 2005; Rutledge 2007).
The long-running debate between neo-Malthusians, who worry about scarcity, and 'cornucopians', who do not, remains unresolved to the present day. It is, in any case, beyond the scope of this book.
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