For roughly the past hundred years, humans have been disrupting the cyclical processes of nature at an accelerating pace. All human societies are, in varying degrees, now processing natural resources in a linear direction. Our resources are being rapidly transformed into useless garbage, some of which is obvious to the naked eye, but most of which escapes awareness. By far the larger portion can be thought of as "molecular garbage" - consisting of the vast quantities of tiny particles that are daily spewed out into the earth's air, water and soil.
With few exceptions, none of this garbage finds its way back into the cycles of society or nature; it is not taken up for repeated use by industry, nor is it put back into the soil. As a result of poor or non-existent planning, the volume of garbage is too large for nature to re-assimilate, and some of it - toxic metals and stable unnatural compounds - cannot be processed by the cells at all.
The ultimate consequences of all this are impossible to foretell. The complexity of ecosystems is so great that we do not know the tolerance levels for any of the thousands of kinds of molecular garbage; it is even more difficult to anticipate how they will interact with each other. In addition, it often takes a long time for the consequences to appear: The effects of today's pollution will not become evident until tomorrow. It is from that perspective we must respond to questions like, "Is the greenhouse effect really a threat, or will it actually prevent another ice age?".
In essence, everything in nature is cyclic. This implies that there must be as much reconstruction of material as there is consumption, and that excess waste must not accumulate in nature. The four conditions for sustainability then are:
Implications
The implications of these inescapable aspects of our ecology have been worked out in terms relevant to the operations of commercial firms and governments, for instance, and are being increasingly applied. The fact that nothing disappears but is simply transformed is exemplified in the cycling of carbon (Section 1.3) and water (Chapter 6). The dispersion of air pollutants (Section 14.7) does not destroy it but merely shifts it elsewhere. The increase of entropy implied in everything spreading refers, for instance, to the sharing of heat by conduction from hot to cold (Section 3.1) and the cascade of wind circulations from relative regularity on the global scale towards the randomness of hot molecules (Table 1.1). The quality (i.e. usefulness) of heat depends on the temperature, which is a measure of heat concentration (Section 3.1) and the versatility of energy is greatest within the well-defined structure of radiation (Chapter 2). Photosynthesis (Section 2.4) is the dominant means of capturing the only permanently sustainable supply of energy, which comes from the Sun.
