There is a twofold reality concerning cities. On the one hand, they are the locus of many of our most well-rehearsed national problems (Amin, Massey & Thrift, 2000), but on the other, they can be considered among the brightest stars in the constellation of human achievement (Rees & Wackernagel, 1996). Therefore, they are sinks of challenges, but also sources of creativity and hope (Amin, Massey & Thrift, 2000).
The nature and variety of challenges which cities have faced during their existence have differed widely. At the very beginning, the first human agglomerations or ‘walled cities’ were shelters against invasion, starvation and wild elements. Then the Greco-Roman cities can be considered the origins of politics, democracy and citizenship but also were centres of slavery and injustice. Much later, the Victorian industrial metropolis was locus of poverty, grime and disease as well as generators of moral revolutions (Amin, 2006). Nowadays cities are recognized as being arenas for social inequalities and major causes of natural resource degradation. Moreover, since the first years of the last century, these problems have been increasing due to the progressive urban population growth. In this sense, according to the last World Urbanization Prospect report, within 40 years almost the 70% of the total population will live in cities (World Urbanization Prospects, 2007). As mentioned by Amin (2006), the human condition has become the urban condition, and hence, the future of mankind is now (more than ever) closely linked to the destiny of our cities.
For decades architects and planners have suggested a wide diversity of models of ‘good city’ in order to tackle the principal urban problems. The ‘Garden City’ (Howard, 1898) was the first city model of the long list (Figure 1 a). According to Howard’s metaphor of the “town-country magnet”, the garden city was the balance required to solve the city-countryside conflict. Then Le Corbusier (1971) formulated first, and much later, implemented his idea of the ‘Contemporary City of 3 million inhabitants’ in the Indian city of Chandigarh. A rational city designed according to human physiology and numerical geometry (Figure 1 c). The 1930s was a decade were the utopian models of good city flourished. First was the Frank Lloyd Wright’s ‘Broadacre City’ (Lynch, 1981; Figure 1 b), and then, a model proposed by Mumford (1938), both authors claimed for a more organic city, namely a city which is in an effective symbiosis with the environment. The next model is called the ‘Compact City’ and it has been around from the early 1990s until our days. It is based on the reductionist idea of conceiving the city in terms of shape and density. In this regard, it has been argued that compactness can reduce energy consumption, pollution and preserve habitats and valued landscapes (CEC, 1990).
Figure 1 Models of good city: a) Howards’ Garden City (Howards, 1898); b) Wright’s Broadacre City (Lynch, 1981); and c) Le Corbusier’s Contemporary City of 3 million of inhabitants (Le Corbusier, 1971).
It has stated that compactness could be one of the dimensions of the new model of good city (Terradas, 2001), the sustainable city. However, can cities really be sustainable? In order to answer this question is essential to define first the word sustainable. On the one hand, we could accept the well-known Brundtland’s Report definition of sustainable development (WCED, 1987), which is a “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”. In this theoretical framework, sustainability is generally understood as a balance between the social, environmental and economical dimensions of development. Therefore, the sustainable city is conceived as static entity within the middle of this triangle, in other words, a green place with a just society and a growth economy (Campbell, 1996).
The author of this work, on the other hand, has based his answer on a new definition of sustainability, which is “development that satisfies the choices of the present, without compromising the ability of future generations to make choices of their own” (Durack, 2001). There is a small but significant change. This new interpretation embraces election, contingency and diversity instead of balance or equilibrium. In this new frame, sustainability, thus, is viewed as a coevolutionary process of a people adapting to, while simultaneously changing, the city over time (Neuman, 2005). Consequently the sustainable city is understood in this paper as an open dynamic process instead of a static point in space and time.
The present work is an attempt to answer the key question whether cities can be really sustainable. As mentioned above, this reply is based on a new and more open interpretation of the sustainability concept. In the first section, the failure of achieving the sustainable city only in terms of shape is analyzed. While in the second section of the essay, the possibilities of sustainable urban process relying on the concepts of ‘urban metabolism’ and ‘urban ecological footprint’ are discussed (note that urban sustainability is a broad issue and this work is focused only in two of its many dimensions).
A sustainable urban form
It has said that whereas time is an explicit dimension in the definitions of sustainable development, space is generally ignored (Breheny, 1992). But since the 80s and early 90s, there has been an increasing concern about the environmental degradation and social deprivation caused by the uncontrolled growth of our cities, what is called ‘urban sprawl’. Some of the problems derived from this are the urban occupation of natural areas, high levels of pollution caused by intense usage of transportation and reduction of social capital (CEC, 1990). It has suggested that the solution of urban sprawl is the mentioned model of compact city. According to Beatley (2003), compactness policies directly translate into much lower energy use per capita, and lower carbon emissions, air and water pollution, and other resource demands. It has also been argued that the compact city provides a superior cultural, social, and economic base for society (CEC, 1990). In this same sense, despite that the word ‘sustainability’ does not appear in any of its pages, Jane Jacobs’ The Death and Life of Great American Cities (Jacobs, 1961) was the first claim for a more dense and functionally mixed city as a solution of social collapse of many American urban communities.
Nevertheless, nowadays it is known that the compact city has raised some crucial contradictions, and hence, it could not be understood as the sustainable panacea. Although urban sprawl has led to longer trips and an increasing dependence on cars which is often associated with energy consumption and greenhouse gases emissions (Muñiz & Galindo, 2005), there are not strong evidences that containment policies promote energy savings. For instance, a study carried out by Breheny (1995) in the UK concludes that energy savings from compact-city proposals would be minimal and that other policies, such as promotion of improved vehicle technology and raising of fuel costs, might be more fruitful. Moreover, even in the case that political, technical and economic impediments were not a problem, there are a lot of doubts concerning the social acceptability of higher densities in many urban areas (Breheny, 1997). Finally, Burton (2000) found that for medium-sized English metropolis, higher urban densities may be positive for some aspects of social equity and negative for others, but when looked at in its entirely compactness has a limited correlation with social equity.
Although it has been argued that urban form and land use patterns are major determinants of urban sustainability (Breatley, 2003), conceiving the city in terms of shape is neither necessary nor sufficient to achieve the goals ascribed to the compact city or other sustainable models. According to Breheny (1992), the relationship between urban shape and environmental sustainability may not be as direct as planners would like. What is more, not all socio-economic and environmental conflicts have their roots in spatial or architectural problems (Campbell, 1996). In this regard, Neuman (2005) argues that the shape of a particular city is just a snapshot of a more complex process, and hence, form is not measurable in terms of sustainability: “one cannot overlook the fact that form is both the structure that shapes process and the structure that emerges from a process”. He also states that we should envision the city as a composite of metabolic processes, what has usually been called the urban metabolism.
Figure 2 Qualitative comparison between the actual urban data and a correlated percolation model: a) three steps of the growth with time of Berlin and surrounding towns; and b) dynamical urban simulations of the proposed model by Makse and colleagues (Makse et al., 1995).
In the next section the possibility of a sustainable urban metabolism will be analyze, but there is still one more thing concerning the urban form that should be discussed here, the relationship between urban form and growth. It has been argued that the properties of human settlements growth emerge from the universal properties of their intrinsic dynamics (Solé & Goodwin, 2000). Therefore, urban planners should understand that city growth and the resulting urban pattern is also caused by an inherent ‘diagram of forces’. As D’Arcy Thompson pointed out in his On Growth and Form (2003), “the form of any portion of matter (living or dead), and the sensible changes of form, that is, its movements and its growth, may in all cases be shown as due to the action of forces”. For instance, urban growth is very sensitive to initial conditions (Page, 2006), intermittency (Zanette & Manrubia, 1997), contingency and other simple forces such as aggregation and diffusion (Makse et al., 1995; Figure 2).
A sustainable urban metabolism
In ecological terms, cities are heterotrophic systems (Figure 3), namely they rely on the primary productivity from other ecosystems beyond their geographical or political boundaries (Folke et al., 1997; Huang et al., 2001; Terradas, 2001). Nearly 40% of potential net primary productivity is used directly, co-opted, or foregone because of human activities (Vitousek et al., 1987). As nowadays the urban population is more than half of the total, more than 20% of the total primary productivity is consumed by human settlements. The same can be said about raw materials, water and other resources and ecological services (Curwell & Cooper, 1998; Warren-Rhodes & Koenig, 2001).
According to Huang et al. (2001), cities are situated in a higher energy hierarchy than rural or natural areas. This idea was stated earlier by authors such as Margalef (1974), which suggested that relationships between neighbor ecosystems are asymmetric (Figure 3), and what is more, the more mature ecosystems absorb energy and resources from the simpler. Examples of this phenomenon can be found in hillslope systems (Terradas, 1982) or even in the interaction between the formal and the informal sector of a country (Moser, 1978).
Figure 3 The city as an open ecosystem. Cities consume natural resources and ecological services and also disperse waste, pollution and heat into the atmosphere, and aquatic and terrestrial ecosystems (based on Terradas, 2001).
The materials, energy and food supplies brought into cities, transformed within them and the products and wastes sent out from the cities are often referred to as the urban metabolism (Huang & Hsu, 2003). The existence and maintenance of cities is extremely dependent on the continuous flows of ecological goods and services (Huang & Chen, 2005) and hence, it is in the self-interest of city inhabitants to make sure that ecosystems continue to produce the biophysical preconditions on which they live (Folke et al., 1997). As Rees and Wackernagel (1996) noted, no city or urban region can achieve sustainability on its own. They go on to argue that regardless of local and land use policies, a prerequisite for sustainable cities is sustainable use of global hinterland. In short, we must reduce the “ecological footprint” of our cities.
In fact, one of the biggest problems that the cities are up against lies in the linearity and unidirectional character of their metabolisms. Girardet (1999) points out that the linear model of urban production, consumption, and disposal is unsustainable and undermines the overall ecological viability of urban systems, for it has the trend to disrupt the biogeochemical cycles. He goes on to suggest that cities need to adopt circular metabolic systems to assure their own sustainability and that of the natural and rural environments on whose productivity they depend. In other words, in addition to the reduction of the city’s use of natural resources and production of wastes, urban systems should improve their resource and energy efficiency through increasing the spectrum of recycling materials as wells as their livability (Huang & Hsu, 2003).
Reducing the urban ecological footprint can be technical feasible, the real problem lies in the change of social values that this effort implies. A “26-year urban metabolic checkup” (Warren-Rhodes & Koenig, 2001) carried out in the city of Hong Kong shows that overconsumption as well as inefficiency in materials, energy, and water use has been caused a systemic overload of land, atmospheric and water systems, but most importantly, these results were not due to the fact of a lack of knowledge or scientific management. Instead, for approximately 30 years the absence of determined government action, concrete goals and a visionary scope have stymied Hong Kong’s ability to improve its environmental record.
In the present work the background, form and processes of the so-called sustainable city have been discussed. In the first section of this works, it is argued that envisioning the city in terms of shape is both contradictory and misleading. For example, the compact city solution, the last model suggested by some academics and decision makers, is surrounded by several doubts concerning both social and environmental issues. In fact, generally there is not a clear relationship between urban form and sustainability. Above all, urban sustainability should consider the processes and flows occurred within and through cities.
In this regard, in the second section of this paper there has been stated that moving towards sustainability means decreasing the urban ecological footprint, through reduction of pollution as well as natural resource and energy use, and adopting a circular urban metabolism, that is promoting recycling policies and increasing the materials’ lifespan. Therefore, first, if cities attempt to be sustainable should ensure the sustainability of the natural ecosystems on whose productivity they rely on, and secondly, the processes of living, consuming and producing in our metropolis should dramatically change.
To conclude, cities are understood here as a composite of processes. City inhabitants, thus, are embedded within a coevolutionary trip with their urban environments. In this context, a city will never be sustainable by its own. Instead, we should make sustainable the processes of building, living, working, consuming and commuting that, at the end, shape our cities. Consequently, urban planning must be an open process which channels the many forces that operate within as well as across the city, thus exploiting the opportunities we have inherited and creating potentials for the next generations. It will be the toughest challenge of our time, but also our biggest hope.
Ramiro Aznar Ballarin
MSc Urban Sustainability (University of Reading)
Sustainable Development essay
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