Last week I introduced the laws of the jungle – those physical and natural laws which, as far as we can tell, govern the behavior of all matter and energy in the universe. I know many readers may be wondering why an urban planning blog is bothering to take the time to discuss such highly abstract and seemingly unrelated material. The reason is actually quite simple – the laws of the jungle govern the operation of the city, and to neglect their importance during a period of energy descent and ecological is foolhardy.
The Age of Exuberance – a period of historically anomalous expansion, growth, and technological development based mostly in fossil fuel exploitation – has obviated planners from having to make tough decisions based on energy scarcity or environmental uncertainty. Over the course of the Age of Exuberance, the limiting factors for planning decisions were based on social, economic, and political factors. However, as energy descent deepens, planners will increasingly find that the limiting factors for planning decisions will be physical in nature. This phenomenon might express itself directly through ecological collapse or indirectly through increasingly high commodity prices. But one thing is clear: the days of ignoring the laws of the jungle are over, so we better start familiarizing ourselves with them.
I began this process last week by introducing the operations of what are called dynamic dissipative systems. Dynamic dissipative systems organize the energy and matter in our universe at every scale, from as small as a molecule to as large as a galaxy. Looking at things from a systems perspective reveals that all systems share some very basic structures and functions. Identifying and studying the fundamental structures and functions of all systems is useful because it allows us to apply what we know about well-understood systems to larger, more complex, and abstract systems – like cities.
This week I will take what we learned last week and build upon it by introducing the basic principles which act upon and guide energy flows in systems. As stated, systems guide the flow of available energy and materials. They use available energy to produce, consume, recycle, and sustain themselves.
The rate that available energy flows through the system – called power – is important, because power is necessary for systems to perform work. Work is just another name for the operations of systems – the producing, consuming, and recycling that they do. Any time available energy is transformed from one kind to another, work is performed. For example, our cities (system) take inputs of biomass and fossil fuels (available energy) at certain rates (power) and transform them into finished goods, information, and experiences (work).
Sometimes when energy is transformed from one kind to another, some of the work accumulates within the system to more-efficiently guide subsequent flows of energy. These accumulations of work are called flow structures. As mentioned last week, urban flow structures are human-made, and may be physical, social, economic, and technological in nature.
Further, these flow structures can be corporeal or intangible, formal or informal. They serve as the organizational framework for where cars can flow, the terms by which people can interact with each other, how money and credit is distributed in society, and the methods by which the work of cities is performed, for example. Without continual flows of available energy that build and contribute to the creation and maintenance of flow structures, systems degrade away.
Energy flows through systems by way of certain physical laws. You may remember from physics class that there are three laws of thermodynamics. The first law of thermodynamics – the law of energy conservation – informs us that energy can be transformed from one form to another, but cannot be created or destroyed. In other words, everything in a physical process must be accounted for, and no energy or material can magically disappear.
The second law – the law of entropy – informs us that for any work to occur, some of the available energy must dissipate along the way as unusable heat. This second law can be thought of as an “energy tax”. In other words, some energy is always lost for each energy transformation performed. This is where the “dissipative” part of “dynamic dissipative systems” comes from.
The third law – that of absolute entropy – informs us that as a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value. This third law doesn’t really apply to everyday life. It deals only with incredibly cold temperatures in deep space.
For our purposes, we will now discuss the implications of the entropy law at length, for this is the one with the most bearing on the operation of our cities when we consider them as systems.
As discussed last week, under normal conditions systems organize themselves to minimize inputs at the local level and maximize output at the macro level. Minimizing inputs is akin to reducing the entropy of energy as it passes through the flow structure of the system. Another way of saying the same thing is that systems organize themselves to maximize efficiency: less energy wasted means more energy can be applied toward the fulfillment of the system’s ultimate goal: maximizing output.
This concept comprises the core of the “Maximum Power Principle”, first stated and described by the American ecologist Howard T. Odum. Odum is known for his pioneering work on ecosystem ecology and general systems theory in the latter part of the 20th century. He insightfully illustrates how the Maximum Power Principle guides the organization and emergent behavior of all types of systems.
The Maximum Power Principle guides the process by which dense webs of efficient relationships between entities build up into distinct hierarchical, branching, and specialized flow structures at all scales. Each transaction of energy and material that occurs within systems leads to four distinct outcomes: some stays at that hierarchical level, some is passed to the next step up in the chain, some material is recycled back downward, and some energy dissipates. These outcomes are consistent with the laws of thermodynamics, as we might expect.
From these basic premises, additional insights present themselves. One of these is that any given part of the flow structure of a system contains what’s called embedded energy. Embedded energy is the sum of the inputs used up directly and indirectly to create output. It is “energy memory.” Embedded energy internalizes all related energy costs, including mineral extraction, processing, production, delivery, maintenance, and decommission.
When applied to city systems, this insight reveals the stark costs that the law of entropy levies against the flow structures of cities. They reveal that each energy conversion within cities results in significant entropy and that each level upward in the complexity hierarchy is reliant on a large amount of embedded energy. Further, they show that cites are utterly dependent upon lower hierarchical levels for their survival.
In other words, cities use profligate amounts of energy in their operation, maintenance, and growth and without these constant energy and material inputs from nature, cities would wither. I’ll talk much more about the energy and material appetites of cities – particularly metastatic cities – in a future post.
It will suffice here to say that cities possess a metabolism which governs its internal processes. The process is as simple as resources like raw materials, food, water, timber, and air – in, and wastes like pollution – out. Many capable scientists such as Geoffrey West, Luis Bettencourt, and James H. Brown have done work on measuring the urban metabolism of cities. Their work reveals that city systems function much like live organisms in the sense that they maintain a metabolic rate dependent upon their size. I will reserve a more-detailed discussion of this subject as well for a future post.
In the meantime, now that we have a modicum of energy literacy we can begin to discuss the way cities interact with the natural systems they depend upon. This will entail a discussion of ecological principles. That’s where I’ll pick things up next week.