Perspective EssayAn expanded urban metabolism method: Toward a systems approach for assessing urban energy processes and causes
Highlights
► We propose an new approach to conducting urban metabolism analysis. ► These will strengthen its utility for policy makers. ► Data remain difficult to obtain and synthesize, but new approaches are emerging.
Introduction
With the industrial revolution and the rise of capitalism, the modern world entered an era of resource exploitation and intensity that it had never before experienced. This industrial revolution, coupled with advances in science as well as the growth of cities and the global economy, laid the basis for the prodigal twentieth century (as McNeill, 2000 writes), that invented processes bringing enormously accelerated social and ecological change, predicated largely on the use of fossil fuels. “No other century—no millennium—in human history can compare with the twentieth for its growth in energy use. We have probably deployed more energy since 1900 than in all of human history before 1900” (McNeill, 2000). Human impacts are transforming the very fundamental processes of nature (Vitousek, Mooney, Lubchenco, & Melillo, 1997); humans are biogeophysical forces, unwittingly altering Earth systems with unknown outcomes.
This resource use intensity and massive deployment of fossil energy for human activities, accompanied by exponential population growth and the trend toward increased urbanization, has resulted in remarkable advances in economic growth, innovation, health, and global interconnectivity—particularly in industrialized economies. Still, the resource consumption of the contemporary era is widely recognized to be greater than the planet can sustain indefinitely (Folke et al., 1997, Wackernagel and Rees, 1996). In order to bring modern society's energy and resource demands into line with the finite resources of the Earth, much more needs to be done to quantify resource use and to understand its political, economic, and ecological context. One promising framework that has been advanced as an approach for quantifying energy and resource use and supply in modern societal systems is that of “urban metabolism.” Urban metabolism offers a platform for greatly expanded urban systems analysis. Researchers such as Newman et al. (1996), commissioned by the Australian government to study the trends of per capita resource input and waste metabolism in Sydney, were early pioneers in linking urban metabolic measures to livability and sustainability analysis. Yet the analyses remained at a descriptive level and did not delve into the social and political drivers of urban form and levels of flows. Much of the discussion was exhortative, stating that industrial areas could look at their flows to reduce waste through industrial ecology principles, or that projects could be assessed for their sustainability using extended metabolism analysis. There was little recognition of the structural (political, economic, social) processes and complexity of change. In this paper, we assess the state and value of urban metabolism for influencing urban sustainability and conclude by suggesting that urban metabolism analysis, to be effective, also requires a political–ecological–theoretical framework and an understanding of power and money.
In the discussion that follows, we attempt to make the case for the expansion of urban metabolism to a more encompassing systems approach. While urban metabolism has been explored by a number of different disciplines such as industrial ecology, ecology, chemistry, and urban planning, studies on cities have tended to be done from each disciplinary perspective. The expansion of urban metabolism to a wider systems-oriented approach requires the collaboration of different disciplines in the analysis of a city's metabolism, in matching energy and waste flows to land uses and social-demographic variables, in evaluation of the socioeconomic and policy drivers that govern the flows and patterns, as well as life cycle assessment of the various processes and materials that make up a city's metabolism. This is a difficult undertaking, necessitating harmonization of units of measure, scale, boundary definitions, and the integration of the human element. Urban systems are sustained by resource flows and they generate waste, and these are driven by policy frameworks (explicit and implicit) and human social organization. Linking the resource base of cities to the human decision-making frameworks they exist in—often political—will provide insights about the contexts that support how urban areas work.
We begin with an overview of urban metabolism first as discussed by Marx, and much later as applied by industrial ecologists and others. We provide an overview of its applications in the current literature and its limitations. We then suggest a new approach to urban metabolism, modified and augmented by socio-demographic and spatially explicit data, greater integration of ecological impacts, considerations of systems-based policies (e.g., climate change and energy), and the situating of urban metabolisms in current political ecology theory (Castree, 2008, Francis et al., 2011, Heynen et al., 2006, Pickett et al., 2011, Robbins, 2004, Zimmerer, 2006). This “expanded urban metabolism” approach is inherently interdisciplinary, requiring the techniques of life cycle assessment, ecological assessment, economic analysis, sociology and policy studies, and the uncovering of systemic interdependencies and interactions that undergird urban energy patterns and processes. It recognizes the multi-level governance challenges faced by cities, including the opportunities for experimentation and learning (Corfee-Morlot et al., 2011, Evans, 2011) as well as the limitations due to the politicized nature of systems policies (i.e., climate change) and declining public sector fiscal capacity. Indeed, expanded urban metabolism is a science and data driven systems approach that should also include how policies at many levels may create specific energy/materials flows. Expanded urban metabolism can help to address one of the most important issues of the day: how to sustain the quality of life for humans without permanently exhausting planetary resources or altering the planetary dynamics that support civilization.
Following Sayer (2000), we are proposing methods that provide concrete analyses of processes that create geographically distinct outcomes. So while there are global trends showing an increasingly urban world (over half of the world's population now lives in cities (UNFPA, 2007), and cities have large impacts on the environment due to their concentration of human populations and resource use (Alberti, 2008), each urban system has its own specificities, including the mix of resource use and social organization as well as governance and position in larger systems (e.g., nation-states or climate zones). The tools of urban metabolism analysis can provide an effective lens into the biophysical processes that are harnessed by cities and conditioned by political–economic structures. This paper proposes that the political and economic forces that make cities grow or shrink are an intrinsic part of the urban metabolism, though complex and highly integrated with nested and tiered political–economic institutions and systems that range from the local to the global (Fig. 1).
We conclude by suggesting that a more interdisciplinary approach to urban metabolism will reveal heretofore hidden ways in which nature is enlisted in the service of urban and economic growth, and that geographic specificity is important. Each place will differ and so will the specific composition of resources and their use. However, localities are no longer isolated and autonomous, thus the ways in which they intersect and are imbricated in larger networks—from resource chains to capital flows—matters to a UM analysis. In this paper, we outline an integrated socio-ecological and socio-technical (Smith & Stirling, 2010) approach to measuring and managing the inputs and outputs of today's urban regions.
Section snippets
Urban metabolism: context and history
Urban metabolism (UM) researchers have compared cities to biological organisms. Organisms need energy and resource inputs, transform them to do work, and produce waste, much like cities do (Bettencourt et al., 2007, Pataki, 2010). Defined as “the sum total of the technical and socio-economic processes that occur in cities, resulting in growth, production of energy, and elimination of waste” (Kennedy, Cuddihy, & Engel-Yan, 2007), UM emerged in the late twentieth century as a systems-based
Urban metabolism in the twentieth century
In 1965, Abel Wolman wrote a pioneering article, “The Metabolism of Cities,” re-launching the UM concept for the engineering community. Wolman (1965) developed a model of a hypothetical American city of one million people to actually calculate the inputs of materials and outputs of waste for such an urban system, taking UM to a quantitative proof of concept. He advanced the notion that urban footprints were no longer constrained to the geographic or political boundaries used to define them.
Measurement methods
Forty-five years after this pioneering work by Wolman and his contemporaries, UM has evolved into two distinct approaches: mass balance accounting and Odum's emergy method. The first is the more widely used energy-materials flux approach (discussed in greater detail below). It is closely associated with the Industrial Ecology and Engineering fields. It incorporates tools of material flow analysis (MFA) to assess the movement of urban materials (and energy) through the urban system (Barles, 2007a
Urban metabolism, the second generation: upgrading the analytical framework by adding spatiality, ecology, and people
In this section we discuss the additional elements UM needs to provide more complete analysis, as well as the theoretical framework to connect its powerful information gathering capacity to the local political, economic, and social context driving these urban systems. It is difficult to set clear boundaries around the intertwined human–natural interactions that need additional studying. How urban ecosystems are created over time, for example, reflects political, economic, natural, and social
Urban ecosystems and ecosystem impacts
Urban activities create novel urban ecosystems. These ecosystems have extensive social and built complexes that have a dramatic effects on ecosystem form and function (Francis et al., 2011, Pickett and Grove, 2009). Anthropogenic urban nature provides ecosystem services, e.g., shading, habitat for fauna, food, purification for water, etc. This kind of human-mediated mixing of species and built complexes is most intense and frequent in urban regions. “Networked global cities exchange organisms,
Disaggregating metabolism
Most urban metabolism studies use highly aggregated data—often at the city or regional level—that provide a snapshot of resource or energy use, but no correlation to locations, activities, or people. Often this is due to a lack of ground-up (disaggregated) data. For various reasons, utilities and other energy managers generally do not provide data at the census block or track level, much less to the resolution of individual bills. Thus there is a fundamental blindness about how much energy is
Theory for complex bio-social urban systems
The biggest challenge facing urban metabolism is the integration of political, demographic, economic, and geographic factors that govern or influence a city or region's urban metabolism. Any city's metabolism is the result of human agency—the ability to exploit ecosystems and their services. This involves scales of governance, institutional rules and conventions, multiple economic forces, and capital flows that shape specific places. Here is where the UM framework is weakest and needs the most
Establishing an expanded urban metabolism framework
Urban metabolism is uniquely poised to offer a unifying framework for quantifying, analyzing, and influencing urban form, function, process, and sustainability. Though the traditional accounting methods described above are insufficient for understanding process and meaning in urban energy patterns, the UM framework lends itself to greater interdisciplinary contributions for the integration of methods and theories that build an understanding of complex urban systems. By integrating the
Conclusion
Urban centers grow in complex ways due to dynamic and interlinked geographical and institutional forces converging upon them (Grimm et al., 2008). Cities are now nearly entirely dependent on access to resources and ecosystem functions outside of their administrative boundaries. They are also, as a result, the primary driver of global environmental change. This includes greenhouse gas emissions that are causing climate change, the decline of biodiversity, and impacts of resource extraction in
Acknowledgments
This research was funded by the California State Energy Commission Public Interest Energy Research Program (PIER). The research program was created when California decoupled electrical generation from distribution to foster research on energy efficiency. The PIER program was not reauthorized by the California State Legislature.
We would like to thank our anonymous reviewers for their insightful comments and suggestions.
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