5.5.1 Definitions and Semantics

Much of the public and scientific debate about biofuels has assumed that the pro­duction of bioethanol as the lead biofuel is inherently “sustainable,” mostly on the grounds that any agricultural activity is renewable, whereas the extraction of crude oil is necessarily a once-only activity, given the extremely long geological time scale of oil’s generation. As a term, “sustainability” suffers from inexactness.7879 As Patzek and Pimentel79 point out, an exact definition can be deduced from thermodynamics and is consequently defined in terms of mathematical and physical properties, that is, a cyclic process is sustainable if (and only if):

1. It is capable of being maintained indefinitely without interruption, weaken­ing, or loss of quality

2. The environment on which this process depends and into which the process expels any “waste” material is itself equally renewable and maintainable

These are very strict criteria and are not exemplified by, for example, an annual replanting of a crop plant such as maize, which depends on outlays of fossil fuel energy (for fertilizers, etc.) and which may seriously deplete the soil or minerals and contribute to soil erosion — although such a system appears to be renewed every year, that is “only” within living memory or the history of agricultural production on Earth, on a geological time scale a minuscule length of time. It is a sad fact of human agricultural activity that periodic crises have accompanied large-scale, organized farming for millennia in (among many other examples) the erosion and salt accumulation that caused the downfall of the Mesopotamian civilization, the overgrazing and poor cultivation practices that have caused the expansion of the Sahara, and the overintensive cultivation of fragile tropical rainforest soils that con­tributed to the collapse of the Mayan economy and society.80 Industrial agriculture and intensive farming are relatively recent arrivals, within the last century, and they have brought accelerated land degradation and soil erosion; agrochemical residues in water courses are a global problem, leading to eutrophication of freshwater fishing grounds and threatening the collapse of fragile ecosystems. To environmental lobby­ists, therefore, the prospect of energy crop plantations is highly unwelcome if such agronomy requires and is dependent on the heavy use of fertilizers, insecticides, and pesticides, the depletion of soil organic carbon, and (worst of all) the sequestration of limited farmland.

A more analytically useful definition of the renewability of “renewable” energy could focus on a more analyzable time scale, perhaps 160 years (approximately, the life span of the industrial activity that underpins modern society).79 Perhaps, even more appropriate would be a century, that is, most of the time in which automobiles have been fuelled by gasoline and diesel. For either option, generating a quanti­tative framework is crucial to any assessment of the practicalities of a biofuels program.