The “metabolism” of human systems has become a mechanism for processing their environmental effects. By rendering them as figures of chemical and energetic flow, metabolism allows for the ultimate impact of technological and social activities to be quantified. But before being acted upon, the space between systemic and human scales must somehow be bridged.
“The energetic processes of an industrial city are like those in a dense reef of oysters.”
To be metabolic is to inhabit a landscape of flows. In a world in which both the technological and the natural are understood ecologically, metabolism has effectively become a catch-all. Any kind of identity, any bounded system amid the flux of material can be defined by metabolic action. All consumers and transformers of matter and energy—from power stations to coral reefs, pine trees to batteries—can be viewed in terms of equality. Metabolism renders them calculable. It captures what they do, and what they are, which in this particular worldview are the same thing.
Originally a biological concept for the activity of life in progress—a secular substitution for the anima, or vital spark—metabolism is now an instrument. Its application to the products of human design—cities, factories, processes, and objects of all kinds—is fundamental to the modern assessment of environmental impact. Metabolism reduces its subject to a nexus of flows, and in so doing enables the generation of environmental currency. When we speak about the embodied carbon of this or that activity, it is to the metabolic reduction of a set of technological processes that we refer to. When we connect any social or economic behavior to a balance sheet of environmental impacts, it is by virtue of the same device.
A metabolism is a figure of chemical flux. It describes the consumption and transformation of energies and chemicals in a certain time and place. Metabolisms are spatial continuities in the panta rhei of ceaseless movement. That is also, in essence, all they are. To seek to understand a city or a society metabolically is, in effect, to admit how little else you really know about it. The granular and complex internal detail is passed over. Neither spatial nor formal schematization of the moving parts are attempted. All that is admitted are the inputs and outputs; a signature of the ongoing and inscrutable activity of self-creation and maintenance.
BANAL — FUTURISTIC
Originating as a radical reimagining of city form in the early 1960s, metabolism has settled into a plain and undemonstrative afterlife embedded in the processes of post-1990s environmental analysis. Within disciplines like Material Flow Analysis (MFA) and Life Cycle Assessment (LCA), it constructs the action and effect of human processes on each other and the environment. Metabolism is synonymous with a definition of activity (whether running an aluminium smelter for a year, driving a lorry down a flat road for an hour, or catching a kilo of sardines). It is the flows between such systems that constitute the most basic ecological reality. In the ecological reading of human techno-society, resources, minerals, fuels, and pollutants are ultimately more salient than objects, products, commodities, or purchases. The latter is only a superficial expression of the deeper motion of the former.
As Lydia Kallipoliti has observed in History of Ecological Design, ecology as a worldview implies an equivalence between technology and nature. Flows become the reality, both of the interior of human techno-society, and of the geo-biosphere outside it. The movement of energy and material across the boundary between the two is the index of human impact. Flows thus take the temperature of atmospheric or extractive crisis. But the source of their diagnostic power—their abstraction from human culture and scale—also makes them frustratingly intangible. The process of making flows visible, of reconnecting them to mise-en-scene of everyday human reality, is a complex project. In an era when design and investment globally are increasingly evaluated against environmental criteria, it is one around which the form of future design can be seen to take shape.
The metabolic city in particular is a field within which this register of visibility is dramatized. For a generation of architects in the 1960s, the idea of urban metabolism captured the ceaseless change of the high-tech city of the future. That their spectacular futurism, viewed down the axis of history, should meet the banal statistical procedures of modern environmental analysis coming the other way is an irony.
But it is an incompatibility which remains in significant respects unresolved, and productive. The field of human social and technological metabolism is one in which intelligence and strategic “dumbness,” form and formlessness, material and media, all intersect and are transformed. For an idea with such a formative presence in the future of the city, metabolism is peculiarly under-emphasized. It is, depending on your position, either a commonplace or an unknown. In bringing its instrumentalization into the foreground, it is the intent of this essay to make its role in producing our shared understanding of the world a little less opaque.
Metabolic knowledge is produced fluxometrically—it consists in the description and measurement of flows of materials and energy. In the increasingly ubiquitous processes of environmental assessment and rating, in which human activities are characterized in terms of their planetary “externalities'' of carbon or embodied energy, metabolism is the ground truth of the analysis. Of all the many organic metaphors with which the city has been burdened through history, metabolism may in the end turn out to be the most consequential.
URBAN METABOLISM—TWO IMAGES
Two images of “urban metabolism” emerged in the 1960s — spurred on by the crises of technology and environmental damage. For a group of architects in Japan, the potential of metabolic readings of the city was the radical destabilization of formal structure. Metabolism: Proposals for New Urbanism, presented by a group of young architects at the Tokyo World Design Conference in 1960, considers metabolism as the animating force of a city characterized by indeterminacy, organic growth, and instability. Containing proposals and essays by Kiyonori Kikutake, Kishō Kurokawa, and Noboru Kawazoe, among others, the manifesto presents a radical transformation of the city; transformed from a static assemblage of monuments and buildings into a flexible and adaptable landscape of modules and circulatory infrastructures. Metabolic space is mobile, changeable, and experientially intense, but also keyed into and linked to natural landscapes and cycles.
The urban proposals of metabolism are less about the identification of such flows in themselves, than the extension of a logic of flux, indeterminacy, and quasi-organic growth and adaptation into the structure of the city. Often, like the contemporary “plug-in” tendency in Europe, the Metabolists adopt a strategy of large-scale megastructural armatures, onto which shorter lived and easily exchangeable components at the scale of rooms and facilities can be arranged. In Kurokawa’s Nakagin Capsule Tower in Shimbashi, Tokyo, erected over 30 days in 1972, the individual mini-apartments are connected to a pair of concrete structural cores which support them and enable circulation.
Few of the built projects of the Metabolists ever realized the idea of a continuously reconfigurable structure in practice, but at the very least projects like Nakagin (or Kenzō Tange’s vast contemporary scheme for Tokyo Bay) achieve a convincing dissolution of the monumental image of architecture into a state of apparent flux.
The group’s aspiration—set out in the introduction to the manifesto—is less about revealing metabolism as an underlying logic or reality, than making it a reality at the level of experience. For architects like Kurokawa, dynamism and reconfigurability offer the city a return to a kind of natural order. Buildings would grow, develop, and respond to their environment like plants respond to climate. And although the speed and adaptability of modern technology are important, society is not of itself innately metabolic—rather metabolism is a serendipitous way to maximize and bring to fulfillment its inherent energy and dynamism.
We should, Noboru Kawazoe wrote, “try to encourage the active metabolic development of our society.” Or as the critic and plug-in enthusiast Reyner Banham argued along similar lines in an issue of Design Quarterly in 1965, “a plug-in city must look like a plug-in city—[people] have to be able to recognize its parts and functions, so that they can understand what it is doing to them, and them to it.”
Presented five years later by the sanitation engineer Abel Wolman in an issue of Scientific American, “The Metabolism of a City” is, by contrast, a new form of analysis for an ongoing crisis.
“The metabolic requirements of a city,” he argues, “can be defined as all the materials and commodities needed to sustain the city’s inhabitants…”
“...As man has come to appreciate that the Earth is a closed ecological system, casual methods that once appeared satisfactory for the disposal of wastes no longer seem acceptable. He has the daily evidence of his eyes and nose to tell him that his planet cannot assimilate without limit the untreated wastes of his civilization.”
In a set of graphs and diagrams, Wolman quantifies the principal inputs and outputs required by a hypothetical American city of one million inhabitants—including water, food, primary energy carriers like petroleum, and outputs like sewage, solid waste, and harmful emissions. In a sense, “The Metabolism of a City” is a natural extension of the models of continuous hydraulic flow in Wolman’s original field to a broader terrain of material and energy flows. Wolman’s principal interest is in the problem of waste—and his intervention responds to mounting public concern over wastewater pollution of the Great Lakes, and the build-up of smog over cities like Los Angeles.
Between the two metabolisms, what is at stake is the question of scale, and the accessibility or legibility of the metabolic process. Metabolist architecture’s longevity as image is in part due to its compelling articulation of indeterminacy or flow on an affective and recognizable level. Wolman’s project is by contrast a visualization of an ultimately remote totality. No one living inside the object of an urban metabolic study sees the metabolic flows they are participating in. On the contrary, the invisibility, in everyday life, of those flows is what motivates the study. The urban metabolism is a given. The task of the analysis is to reveal it, and this visibility is a precondition of regulating its effects.
The history of urban theory is replete in organic metaphor. In eighteenth-century France, a sense of the city as physiological was formed which endures in commonplaces of language today—the description of major streets as arteries, or urban texture as tissue. If the city is a body, it may be in rude or fragile health. Treatment, as in the Haussmannization of Paris, may be surgical. In later models, the city became less a body than an organic cell or unit—bounded, right-sized, internally integrated and self-regulating, intractable in the face of crude mechanisms of intervention; or, the product of quasi-natural evolutionary forces, shaping itself in response to shifting terrain and external demands. In postwar cybernetics, the city organism is a kind of neurology, self-governing and self-signaling, constructing feedback loops and networked relationships of increasing abstraction and scale. The analogies may be mutually complementary or inconsistent—the rhetoric of the organism has certainly been used as being vehemently in support of the modernist project, as well as in its condemnation.
Urban organicisms provide cognitive maps for intervention. If the city is a body, then knowledge of its anatomy will be through dissection. If it is more like an ecosystem, then the methods of ecological surveying may be more appropriate. In a neurological system, the graphing and modeling of higher level networks seems most likely to capture the core dynamic at work.
Analogies to bodies or cells are at least partially structural; by contrast, metabolism is basically formless. In a sense where all other organicisms say something about what an object is, metabolism only identifies what it does. Where other organic analogies identify systems of homeostatic self-regulation (or even intelligence), metabolism is essentially dumb. The city metabolic is stripped of all pretension—in the sense of culture, value, signification, meaning, or even intent. It is digestion rather than intention. It has no goal, no instinct, no purpose. The identification of human processes as metabolic has no implication of balance or sustainability; on the contrary it identifies the absence of these forms of regulation.
As a method of analysis, metabolism is powerfully, even vulgarly, reductive. Some of the earliest metabolic experiments are those of the Venetian doctor Santorio Santorio. Having identified a mass imbalance between the food and drink he consumed and the quantity of feces and urine he produced, he became determined to measure the body’s loss of mass through perspiration, sitting on a huge steelyard scale over a period of several hours after meals to track his gradual change in mass.
The experiment captures an essentially minimal definition of metabolism as a measurement of flows in and out of a system, captured, in this case, partially by the principle of mass balance. These flows are concretely knowable and quantifiable—where the interior of the system (or body) can only be inferred. The boundary of the metabolism is where information is gathered—its interior is, epistemically or tactically, indeterminate.
This last part is significant—the project of metabolic analysis of everyday life can be seen as premised at a certain level on the idea of creating a feedback loop which didn’t previously exist; between human activities, from purchasing products to designing buildings, and their large-scale planetary impacts. Metrics like embodied carbon or environmental footprint read as attempts to produce a systemic kind of awareness within systems which are not inherently intelligent.
AMONG THE FLUXOMES
What is at stake in the visibility or transparency of metabolic flow or action at the scale of human life and interaction has become clear only in recent decades, as the focus of environmental management and reform has shifted from centers of production to the field of consumption.
In Wolman’s time, the principal focus of environmental design and management was what was termed “the end of the pipe”—the primary operation and effect of large-scale infrastructures and processes. In the last few decades, a secular shift has taken place in which the field of consumption—the “demand side”—is increasingly targeted.
For that shift to be possible, a connection has to be forged between the fluxometry of the metabolic processes at issue—cities, factories, industries, regions—and the scale of human interaction. Products, buildings, projects have to be rendered as fluxomes—that is, as sets or bundles of flows; each one as a miniscule impetus one way or another in the shifts and swells of planetary-scale flux.
FROM LIFECYCLES TO PLATFORMS
Within contemporary practices of environmental assessment, the definition of human activities in metabolic terms is a well understood process. The fluxes of materials, energy, heat, waste, vapor in and out of a factory, or the process of vehicle transport as a flux of hydrocarbon being turned into emissions can be straightforwardly quantified and characterized.
But the metabolic characterization of an object—a shoe, or a building—is a more complex problem. Objects move around, and they don’t remain themselves but are assembled, broken down, used up, and so on. They move through space and time and are inhabitants of a sequence of different processes as they are refined, assembled, sold, used, and discarded.
Starting in the 1980s and 1990s as a mechanism for evaluating the impact of projects and investments, Life Cycle Assessment has become the dominant procedure for the formation of environmental objects—that is, objects formed around a visualization of their external environmental impacts. The principle of these exercises, as is well known, is to give a structural breakdown of externalities by stage. These stages are themselves fractions or abstractions of metabolic analyses of processes. The flows associated with a vehicle are subdivided and attached to the objects they deliver; those of a factory are used to characterize the products they create. Some of these processes are directly surveyed, others are generic data from shared databases and software platforms.
Life cycle “system boundaries” are extended over periods of time and build in scenarios about future performance, as in the energy costs of consumption in use or the carbon intensity of recycling or disposal. The energetic cost of recycling an item must include its life cycle cost today—even though that process may take under a future energy regime of a very uncertain nature. How much carbon will the electricity used to recycle a product emit in thirty years? What mechanisms of safe disposal or reuse will be available? These processes of composition and decomposition, of generation and projection, are behind apparently definitive ascriptions of environmental impact like carbon intensity, environmental footprint, and embodied energy.
Life cycles are increasingly a protocol for more complex systems of assessment. In Environmental Product Declarations (EPD) they are attached to products and commodities, which in turn are integrated into larger-scale assessments. An LCA at the scale of a building necessarily integrates a whole stack of product scale LCAs for its various elements. Recent projects have attempted to integrate these directly into CAD and Building Information Modeling (BIM) software—like the EC3 “carbon calculator” project run by Skanska, Microsoft, and others. Platforms are embedded at both ends of the process—in the definition of industrial processes as generic data (thousands of which are contained on the widely used Ecoinvent database) or in the use of EPDs (or increasingly their machine-readable form—the ILCD) themselves on comparative databases.
The ambition of these processes in aggregate would, in theory, be to allow a city or economy to see its own environmental impacts in plain terms; for a given element—a brick, an air conditioner—a corresponding increase in atmospheric carbon. The objects of everyday life are gradually rendered into environmental simulacra of themselves.
LANDSCAPE OF FLOWS
A world of ubiquitous life-cycling is one constructed by a strange looping, in which the objective metabolic signal and the cultural system it is meant to correct are constantly overwriting one another.
Processes in the technosphere are frequently entangled or folded together, and can be separated only by interpretation. A chicken farm might produce chickens, eggs, chicken manure. A blast furnace might make pig iron, blast slag, and heat. There is no inevitable way to determine which of these are responsible within the system for the externalities of the process from which they originate. On what basis, for example, are the carbon dioxide emissions of a process that takes in iron, coal, and electricity—and produces slag, pig iron, and heat—apportioned to one output or another? Which of the “products” causes them?
In construction, a common means of reducing the carbon emissions of concrete is to replace some proportion of the Portland Cement binder with Ground Granulated Blast Slag (GGBS) from steel production. Cement is the most carbon-intensive ingredient of concrete and produces around 0.9 tonnes of CO2 per tonne of cement, the majority from the process of calcination. Slag is produced in the smelting of steel from ore at a rate of around 150kg per tonne of steel, in a process that produces between 1.9 and 2.3 tonnes of CO2 per tonne of pig iron. In purely metabolic terms, slag, pig iron, carbon dioxide, and heat are all outputs of the process, but the carbon dioxide and other externalities are bundled with the lifecycle of the steel, allowing the slag to escape as a pure byproduct. If, in some sort of peculiar mirror world, the aim of the smelting process was to produce the slag, rather than the steel, it would emit 12-15 tonnes of CO2 per tonne of GGBS.
Current best practices supply a number of answers to these questions. You can apportion the externalities by the economic values of the outputs, or their relative masses. You can separate waste from products on a categorical basis—on what the process produces on purpose, rather than as a “byproduct.” You can make a determination about what people would do instead, if the product didn’t exist; of what they would stop doing if it became cheaper or more plentiful. But in any of these, the apparently external objective signal and the object of the analysis have to be recalibrated within and against the same cultural systems and assumptions they are proposing to enlighten, in some cases in ways which are circular. The connection between metabolism as a reality and our part is mediated in ways that end up obscuring the signal.
For ecologist Peter Haff, this problem is innate to the human “technosphere.” Metabolic flows, and human actions and choices, are one and the same system, but with radically incompatible appearances and variables. The same coarseness of grain that makes a leaf appear as a cellular landscape at one scale and a discrete object at another is diagnostic of the separation of “strata” in complex systems. What is visualizable in the imaging of regional or continental magnitudes as one set of variables will appear at the scale of everyday human agency as something altogether different—and though the planetary emergency manifests at the uppermost stratum, the control mechanisms, such as they are, are all on the one below. Humans, Haff has observed, “are components of a larger sphere they did not design, do not understand, do not control, and from which they cannot escape.”
At the scale of cities, countries, and larger processes we see fluxes, but at the scale of human agency these fluxes are naturally obfuscated. We visualize and interact, not with fluxes, but with objects—buildings, commodities, products, and so on—within which these planetary movements are no longer in any natural sense visible. Not only are the variables of the higher stratum invisible, but the connection of the object to them is unclear.
Between our own stratum and those below, Haff has observed, we necessarily make use of microscopes, centrifuges, probes, and manipulators of different kinds, to interfere in a set of variables which are otherwise inaccessible.
If the entangled crises of overextraction, pollution, and carbon emissions are the result of a disordered material culture, then their solution would appear to be some form of governance. To find some way of connecting the strata—of forming some kind of techno-social microscope—is the precondition for holistic regulation and self-correction of the material system. Governance is made possible by technology. The modern state was formed on top of such instruments—from land surveying to accounting, censuses to CCTV.
If the ambition of metabolism is to re-stabilize the relationship between the city and its geo-biophysical hinterland, it will necessarily do so according to a particular pattern. The self-awareness of the post-Anthropocene city will be maintained by fluxometrics, and will reproduce the specific structures and qualities of that technique. Metabolism connects the world above with that below through a double translation. First, familiar objects are subsumed into an impersonal landscape of chemical fluxes. Then these flows are subdivided and re-apportioned to the human processes which caused them—as “environmental impacts.” The incompatibility of these systems of knowledge—the field of flows versus the discrete catalog of objects—make occasional breakdowns in the system of environmental value to some extent unavoidable. The flexibility of metabolism as a concept is what bridges from the inside of human culture to the planetary exterior and then back again.
The naturalistic analogy, as applied to human processes, thus produces an ambiguous relationship to nature itself. As a definition of processes through chemical flux, applied universally to man-made and non-human activities, the idea of metabolism in a sense abolishes the qualitative distinction between one and the other. What remains, rather, between the human and nonhuman, the biosphere and the technosphere, is a necessary but purely dogmatic separation between two equivalent fields. This separation is at the most fundamental level the “reality” of the metabolism itself, what allows it to capture information.
As environmental indices become an increasingly embedded corrective to patterns of human design and production, it becomes important to identify the forms and techniques by which such systems are produced and maintained. In a world of ubiquitous environmental indexing or carbon calculation, our shared reality becomes the fluxometrics of human processes. The more we internalize, in the design of our cities, a calculus of environmental impact as a social or technical good, the more we become the citizens of fluxopia. In visualizing our shared metabolism at decisive scales and locations, the objectivity of the original signal possessed is lost by degrees. We can become aware of our own impact only through first making it thoroughly unrecognizable; the world transformed so it can ultimately remain more or less itself. It is this slow, recursive self-correction whose signature we may expect to read again and again in the developing structures of planetary self-awareness.