A feature of natural systems that frequently confounds analysts is that of emergent behavior, in which even a detailed knowledge of one level of a system is insufficient to predict behavior at a different level. An obvious example is the beating heart. At its lowest level, the heart consists of cells, of course, which can be described extensively from physical and chemical perspectives. Little at the cell level suggests electrical activity that leads to rhythmicity at higher levels, however. Rather, rhythmicity of the whole heart arises as a consequence of the electrical properties of numerous intracellular gap junctions, and as modified by the three-dimensional architecture and structure of the organ itself (Noble 2002); it is a property, unanticipated at the cellular level, that suddenly emerges at the level of the organ.
Ecological ecosystems demonstrate emergent behavior as well, behavior in which a system may flip from one metastable state to another (Kay 2002). A common example is shallow lakes, often known to be bi-stable (Figure 1.3): if low in nutrients, the water is generally clear; if high in nutrients, it is generally turbid. The transition is not gradual, however, but rapid once a bifurcation point is crossed. This behavior is related to the biological communities involved. Some nutrient conditions favor algae feeders that reduce turbidity, whereas others favor bottom feeders which increase it. The turbidity, and especially the unanticipated flip from one state to another, results both from the general conditions of the system (e.g., temperature, water depth) as well as from the particular types and number of organisms that comprise it and whose
■ Benthic attractor
Increased energy in the water column
Figure 1.3 The bi-stability pattern in a shallow lake. Adapted from Scheffer et al. (1993); courtesy of J. J. Kay.
populations evolve with it (van Nes et al. 2007). That is, the lake is a component of, and subject to, higher-level components, as suggested on the left side of Figure 1.4.
Emergent behavior is also a feature of human systems. Consider the example of cellular telephony. This complex technology was developed in the 1980s and 1990s. The fixed-location base stations that were originally needed were few, and the telephones expensive and briefcase-sized. Cell phone use and the infrastructure that supported it were largely predictable, and users were anticipated to be a modest number of physicians, traveling salespeople, and others not having convenient access to a landline phone. Around the year 2000, improved technology made cell phones much smaller and much cheaper. Parents began to buy cell phones for their children, as well as for themselves. Suddenly it became possible to call anyone from anywhere. Demand skyrocketed, especially in developing countries where the technology made it possible to avoid installing landline phones almost completely. As a result, an entirely new pattern of social behavior emerged, unpredicted and certainly unplanned.
The cell phone story is relevant here because sustainability ultimately involves humans, resources, energy, and the environment. The production of hundreds of millions of cell phones demands an incredible diversity and quantity of materials for optimum functionality. At one point in their rapid evolution, tantalum came into short supply, and the mineral coltan was mined in Africa by crude technological means to fill the supply gap, doing significant environmental damage in the process. The worldwide cell phone network is now trying to address a new emergent behavior: the recovery of precious metals from discarded cell phones through primitive "backyard" technologies. This social-technological activity did not exist when cell phones were few; however, as they became abundant, the recycling networks flipped into a new and unanticipated state.
The adaptive cycle provides considerable perspective on the interpretation of human-natural systems as they undergo evolution and transition. Consider the industrial ecosystem of Barceloneta, Puerto Rico, described more fully by Ashton (2008). This system underwent a major shock in the 1940s and 1950s, when sugar industry exports declined markedly, as did the use of the land for agriculture. From the mid-1950s through 1970, a shift toward manufacturing-based industry resulted in a rejuvenation of the island's economy and a substantial increase in the island's energy infrastructure, the latter based almost entirely on imported fossil fuels. Over the following twenty years, pharmaceutical industries were added, and the industrial system began to exploit Puerto Rico's limited freshwater resources. Currently (2009), manufacturing is contracting, perhaps signifying the beginning of a new collapse of the cycle. It is clear that this story involves interlocking issues regarding the short- and longer-term sustainability of industry, water, energy, agriculture, land use, social behavior, governmental policy, and environmental implications. It is equally clear that the issues were addressed in isolation, with less than optimal long-term consequences for a number of them.
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