>My point is that some
>specifically named natural phenomena might reach exhaustion, but there
>is no record of any reversal of the increasing rate of interchange
>between man and nature, ever.
This may be true from a general perspective, but there have been dozens of regional reversals in recorded history, plus hundreds and perhaps even thousands of local reversals, stretching back ten thousand years. The archaeologist Joseph Tainter discusses many of these reversals in _The Collapse of Complex Societies_ (Cambridge, 1988). He dismisses resource depletion as the least persuasive explanation for social collapse. But that doesn't mean the interchange between society and nature doesn't decrease catastrophically upon general collapse. Here's Tainter's description of the collapse of Mesopotamia following 4000 years of large-scale civilization:
***Sometime in the seventh through tenth centuries AD, however, there was a major collapse in the Mesopotamian alluvium. By the eleventh or twelfth centuries AD the total occupied area had shrunk to only about six percent of its level 500 years earlier. Population dropped to the lowest point in five millennia. State resources declined precipitously. In many strategic and formerly prosperous areas, there were tax revenue losses of 90 percent or more in less than a single lifetime. People rebelled and the countryside became ungovernable. By the early tenth century irrigation weirs were nearly all confined to the vicinity of Baghdad... [and] the basis for urban life in perhaps 10,000 square kilometers of the Mesopotamian heartland was eliminated for centuries. Until the modern era the region was claimed primarily by nomads.***
Tainter argues that collapse such as this cannot be attributed to external factors, such as resource depletion, invasion, natural disaster, etc. Instead, the cause is a result of economic structure. Once a society takes the path of complexification, it inevitably renders itself vulnerable to collapse. Here's how he frames the problem:
***More complex societies are more costly to maintain than simpler ones, requiring greater support levels per capita. As societies increase in complexity, more networks are created among individuals, more hierarchical controls are created to regulate these networks, more information is processed, there is more centralization of information flow, there is increasing need to support specialists not directly involved in resource production, and the like. All of this complexity is dependent upon energy flow at a scale vastly greater than that characterizing small groups of self-sufficient foragers or agriculturalists. The result is that as a society evolves toward greater complexity, the support costs levied on each individual will also rise, so that the population as a whole must allocate increasing portions of its energy budget to maintaining organizational institutions. This is an immutable fact of societal evolution, and is not mitigated by type of energy source.***
We invest in complex systems because they provide seemingly miraculous returns on their initial investments. But as they get larger, they become more unwieldy and more of a drain on resources.
***It is the thesis of this chapter that return on investment in complexity varies, and that this variation follows a characteristic curve. More specifically, it is proposed that, in many crucial spheres, continued investment in sociopolitical complexity reaches a point where the benefits for such investment begin to decline, at first gradually, then with accelerated force. Thus, not only must a population allocate greater and greater amounts of resources to maintaining an evolving society, but after a certain point, higher amounts of this investment will yield smaller increments of return. Diminishing returns, it will be shown, are a recurrent aspect of sociopolitical evolution, and of investment in complexity.
[...]
Four concepts discussed to this point can lead to an understanding of why complex societies collapse. These concepts are:
1. human societies are problem-solving organizations; 2. sociopolitical systems require energy for their maintenance; 3. increased complexity carries with it increased costs per capita; & 4. investment in sociopolitical complexity as a problem-solving
response often reaches a point of declining marginal returns.***
According to Tainter, the vicious circle sets in when worsening economic crisis is "solved" by new efforts at complexification (or other misguided, short-term solutions) that exacerbate the crisis further, followed by yet more complexification, and so on, and before you know it the whole project of civilization falls to pieces. His discussion of the Western Roman Empire in this context is extremely persuasive, not to mention just a little unsettling.
What's different today is that the collapse of complexity could occur at a global scale. If such an event came to pass (and Tainter discusses this possibility at length) it would mean that for the first time the overall interchange of energy between humanity and nature would decline, and it would do so rapidly and catastrophically.
Ted