Crise écologique globale, réponses urbaines

Crise écologique globale, réponses urbaines
Sommaire de l'article

Les villes consomment de nombreuses ressources naturelles et émettent des pollutions croissantes. Ce constat n'est pas une fatalité mais le résultat d'un urbanisme oublieux des contraintes écologiques. Il est donc urgent de transformer les villes pour en faire un élément de la réponse nécessaire à la crise écologique globale. Un agenda politique.

Box 1

Cities are a type of socio-ecological system that has an expanding range of articulations or interactions with nature's environment and ecologies. Today, most of these articulations are negative and produce environmental damage. This chapter examines how we can begin to use these articulations to produce positive outcomes - outcomes that allow cities to contribute to environmental sustainability. The complex internal systems of cities and their multi-scalar character - in terms of geography, policy, society, economy, space and time - have massive potential to effect a broad range of positive articulations with nature's ecologies.

The massive processes of urbanization underway today are inevitably at the centre of our environmental future. It is in cities and vast urban agglomerations that humankind is increasingly present on the planet, and largely through cities that people use various stocks and flows of environmental capital. The hinterlands supplying urban areas, once mostly-confined geographic zones, are global hinterlands today. With the expansion of the global economy, we have raised our capacity to annex larger portions of the planet to support a limited number of industries and places (Girardet 2008). In this chapter, I address the multi-scalar character of cities: the diverse terrains and domains, many non-urban, onto which they project their effects and from which they meet their needs. I address cities' ecological features: the multiple mechanisms and feedback loops that articulate urban processes and their consequences. Furthermore, I examine the emergent articulations or interactions between these urban ecologies and nature's ecologies. The multi-scalar and ecological features of key city processes need to become part of urban governance, so that the process of governing cities becomes part of the process for developing a more environmentally sustainable and ecologically efficient society.


Urbanization and industrialization have made humankind the biggest consumer of all significant ecosystems. Urbanization is an enormously distinctive presence that contributes both directly and indirectly to changing a growing range of nature's ecologies, from the climate to species diversity and ocean purity. It also leads to the formation of new, negative environmental conditions, such as heat islands, ozone holes, desertification and water pollution -resulting in a set of global ecological conditions never seen before.

Major cities have become distinct socio-ecological systems with planetary reach (Sassen 2006). The needs of cities and their increasing populations, and the profit motives of agribusiness, have altered traditional rural economies and their long-standing cultural adaptation to biological diversity. Increasingly, rural populations have become consumers of goods, including even food, produced in the industrial economy, which is much less sensitive to biological diversity. The rural condition - the physical as well as cultural and mental aspects of rural life - has evolved into this new system of social relations, one that does not support biodiversity. These developments all signal that the urban condition - the built environment along with urban cultures and lifestyles - is a major factor in any environmental future, and amounts to a radical transformation in the relationship between humankind and the rest of the planet.

But is it urbanization per se that creates environmental problems, or is it the particular urban systems and industrial processes we have implemented? Are negative global ecological conditions the result of urban agglomeration and density, i.e. the urban format? Or are they the result of the specific types of urban systems we have developed, i.e. the urban content - meaning the transportation, waste disposal, building, heating and cooling, food provision and industrial processes through which we extract, grow, make, package, distribute, and dispose of all the foods, services and materials we use? It is, doubtless, the latter - the specific urban systems we have made: systems and processes we have created collectively and historically, partly through path-dependence dynamics that kept eliminating options as we proceeded, and partly because of corporate profit motives.

When we examine a range of major cities today, one outstanding feature is the sharp differences in their environmental sustainability. These differences result from diverse government and industrial policies, economic bases, cultures, community norms and lifestyles. For a particularly strategic angle that cuts across all these factors, see Box 1, Ecological Economics. For the impact of environmental destruction on generating refugee flows, often directed to cities, see e.g. Warner et al. (2009) and Reuveny (2008). For the differences in impacts on the rich and poor in cities, see e.g. Morello-Frosch et al. (2009); Environment and Urbanization (2007). For the development of urban agriculture as a major response see e.g. Van Veenhuizen and Danso (2007). Government and corporate policies are mutable - as seen in the two following examples from the 2007 U.S. Conference of Mayors. They demonstrate that good urban leadership by elected officials and informed individuals can make an enormous difference in a country often thought to be deeply anti-regulation and generally opposed to government-run programs.

The first case concerns energy systems and a city in Texas, a state best known for its devotion to oil, and shows how the determination to "green" a city can be developed and implemented even when the larger political landscape is not supportive. In 2000, Austin began to implement a "Green Buildings Program" that has been recognized internationally as a model. It is transforming the local construction market by providing education, marketing and monetary incentives to develop both the demand side (the buying public) as well as the supply side (building professionals). The program is primarily funded and managed by the city's community-owned utility, Austin Energy. This municipal utility also develops renewable energy sources for the city, including 59 local wind-turbines, four landfill methane gas recovery projects and three solar energy sites, providing over 153 kilowatts of energy. Austin happens to be the only city in Texas run by a Democratic mayor; Texas is often thought to be one of the most Republican, free-market, anti-government, anti-regulation states in the U.S. It shows how a well-designed effort and determination can succeed even in apparently inhospitable situations.

The second case concerns Chicago, which has an economic history of heavy manufacturing, steel mills, agribusiness and the most important heavy-haul transportation centre in the country. Today, Chicago is determined to establish itself as a premier environmental city, with the goal of obtaining 20 percent of its energy from renewable sources within the next five years. This includes solar, wind, biomass, small hydropower and tapped landfill gas. Chicago has planted thousands of trees over the last five years, created more than 100 miles of bike paths in the city, installed solar panels on city museums and built a rooftop garden on City Hall. The city government has also passed legislation to reduce urban "heat island" effects by allowing only reflective roofs or living roofs covered with vegetation.

These examples demonstrate that policy and proactive engagement are critical dimensions for environmental sustainability, whether they involve asking people to change their energy consumption habits, or insisting governments pass sustainability-oriented legislation, or demanding accountability from local and global corporations known to have environmentally damaging production processes.

A few foundational elements that dominate our way of doing things, and that are at the heart of what we need to address, recur across different cities. One is the fact that the energy and material that flows through our human economy returns in altered form as pollution and waste to the ecosphere. The crux of the matter is that this set of flows is made and can be unmade, as is signalled by the two prior examples from a country that has lagged in environmental standards compared to other highly developed countries. This rupture is present in just about all economic sectors, from urban to rural. However, it takes on its most complex interactions and cumulative effects in cities. Cities are the source of most environmental damage, and some of the most intractable conditions feeding the damage.


The diverse issues affecting the environment can be conceived analytically as questions of scale. Importantly, cities incorporate a range of scales at which a given ecological condition functions, and in that sense cities make legible the notion of scaling. For instance, one asphalted street in a village and a few buildings with air conditioners produce some heat emissions; thousands of such streets and buildings in a city produce a new socio-ecological condition - heat islands. This in turn implies that cities make the multi-scalar aspect of ecological systems legible to residents of cities. The urban environment's capacity to make legible should be developed and strengthened, because such legibility will become increasingly critical for policy matters concerning cities, as well as regions beyond urban areas.

Scaling is one way of handling what are now often seen as either/or conditions: local vs. global, markets vs. non-market mechanisms, green vs. brown environmentalism. Some of the analytic work on scaling being done among ecologists has proven very illuminating in my efforts to conceptualize the city in this context (e.g. Dietz et al. 2009). Of particular relevance is the notion that complex systems are multi-scalar systems as opposed to multilevel systems, and that the complexity resides precisely in the relations across scales. An important issue raised by scaling in ecological research is the frequent confusion between levels and scales: what is sometimes presented as a change of scales is actually a translation between levels. A change of scale results in new interactions and relationships, and often a different organization. Level, on the other hand, is a relative position in a hierarchically-organized system. Thus, a change in levels entails a change in a quantity or size rather than the forming of a different entity. That said, in some cases an expanded quantity or size can indeed become a different scale, as in the case cited below of an illness that becomes an epidemic by spreading to vast numbers of people.

The ecological literature finds that tension among scales is a feature of complex ecological systems, a condition that would certainly seem to hold for cities. Let me illustrate with an example whereby providing an air-conditioned hospital is likely to be experienced as a positive element in any neighbourhood of a large city or small town: it would be difficult to see the negatives for the average resident. But at the scale of the city, the air-conditioned hospital contributes to heat islands, which produces a tension between the advantage for that neighbourhood and the damage to the larger environment, where it accentuates growing ozone holes. This tension among the different scales forces the issue of environmental damage and the need to find and develop solutions at all levels. In brief, understanding how tensions among the multiple scales that might be operating in the context of the city enhances the analysis of environmental damages associated with urbanization. And it enhances our understanding of the ways in which cities are the source for solutions to such damages.

A crucial analytic operation here involves giving spatio-temporal scaling to the object of study (Sassen 2005; for a theoretical treatment about how to construct the object of study, see Sassen 2008; for an application see e.g. Porter et al. 2009). This also entails distinguishing the object of study from contextual variables, which in the case of cities might be population, economic base, etc. Executing such analytic operations would help us avoid the fallacy of holding "the city" guilty of environmental damage. Eliminating cities would not necessarily solve the environmental crisis. We need to understand the functioning of and the possibilities for changing specific city-related systems: energy systems, economic systems, transportation systems, et cetera, which entail environmentally unsound modes of resource use. The fact that these various systems are amalgamated in urban formations is a condition analytically distinct from the systems involved. The distinction between specific systems and background or contextual variables also helps us avoid the fallacy of seeing "the city" as a container, a boundaried, closed unit. In my research on cities and globalization, I instead conceptualize the city as a multi-scalar system through which multiple, highly specialized cross-border economic circuits circulate. This idea can be applied to cities and the environmental dynamic by conceptualizing the city as a multi-scalar system through which multiple specific socio-ecological circuits traverse. Rather than a closed system, cities are amalgamations of multiple "damage" circuits, "restoration" circuits and policy circuits.

Specific issues raised by research on ecological systems point to possibly fruitful analytic strategies for understanding cities and urbanization processes, both in terms of environmental conditions and in terms of policy. One of the reasons this may be helpful is that we are still struggling to understand and situate various types of environmental dynamics in the context of cities, and wondering how to engage policy. When it comes to remedial policy and cleaning up environmental damage, there is greater clarity in understanding what needs to be done. But understanding the city as a broader system poses enormous difficulties precisely because of the multiple scales that constitute it, both as a system of distributed capabilities and as a political-economic and judicial-administrative system. That is to say, the individual household or firm or government office can recycle waste, but cannot effectively address the broader issue of the excess consumption of scarce resources; the international agreement can call for global measures to reduce greenhouse emission levels, but depends on individual countries, cities, households and firms to implement many of the necessary steps; and the national government can mandate environmental standards, but it depends on systems of economic power and those of wealth production.

Some kinds of international agreements are crucial, for instance, when they set enforceable limits on each national society's consumption of scarce resources and their use of the rest of the world as a global sink for their wastes, with protection against biopiracy one of the most extreme cases (Mgbeogi 2006; Gupta 2004). I find other such agreements problematic, notably the one for carbon trading, which has mostly negative incentives for firms in the highly developed countries: firms need not change their practices insofar as they can pay others to take on their pollution, which could mean no absolute reduction in pollution.

A key analytic step is to decide which of the many scaled ecological, social, economic and policy processes are needed to explain a specific environmental condition (whether negative or positive) and design a specific action or response. Another analytic step is to factor in the temporal scales or frames of various urban conditions and dynamics: cycles of the built environment, of the economy, the life of infrastructures and of certain types of investment instruments. The damage produced by a car's unclean motor spewing fumes is immediate, and promptly visible; but when the car is not running, it is not, strictly speaking, producing damage. The damage produced by a building's outside walls does not stop; it is constant and relentless, and it is not as legible as a car's fuming motor. The combination of these two steps helps us deconstruct a given situation and to locate its constitutive conditions in a broader grid of spatial, temporal, and administrative scales.

In the case of cities, the connection between spatial and temporal scales evident in ecological processes may prove analytically useful for approaching some of these questions. What may be found as negative at a small spatial scale, or a short time-frame, may emerge as positive at a larger scale or longer time-frame. For a given set of disturbances, different spatio-temporal scales may elicit different responses from ecosystems. Using an illustration from ecology, we can say that individual forest plots might come and go, but the forest cover of a region overall can remain relatively constant. This raises a question as to whether a city needs a larger system in place that can neutralize the impact on the overall system of major disturbances inside the city. One outcome of the research by ecologists in this domain is that movement across scales brings about change, which is the key process in multi-scalar systems: it is not only a question of bigger or smaller, but rather that the phenomenon itself changes. Biological processes are good examples: the pest that is experienced as pure damage at one scale becomes the food for another species and is experienced as benevolent at that scale. In the case of cities, we can return to the previous example of buildings and heat islands as one illustration. This multi-scalar dynamic also allows us to recognize that an unstable system at a given scale can be a condition for stability at a lower or higher scale. We can extend this process of changing valence, or the capacity of one thing to react with or affect another, to other features of systems: bottom-up control turns into top-down control; competition becomes less important. This also is suggestive for thinking about cities as the solution to many types of environmental damage: what are the scales at which we can understand the city as contributing solutions to the environmental crisis?

Relating some of these analytic distinctions to cities suggests that one way of thinking of the city as multi-scalar is to note that some of its features, notably density, alter the nature of an event. The individual occurrence, e.g. a high-rise building, is distinct from the aggregate outcome, e.g. density. It is not merely a sum of the individual occurrences, i.e. a greater quantity of occurrences. It is a different event. The city contains both occurrences and aggregate outcomes, and in that regard can be described as instantiating a broad range of environmental damage that may involve very different scales and origins, yet still become manifest in urban terms. For instance, CO2 emissions, produced on the micro-scale of vehicles and coal burning by individual households, become extensive air pollution that covers the whole city, with effects that go beyond CO2 emissions per se. Air and water-borne microbes materialize as diseases at the scale of the household and the individual body, and become epidemics thriving on the multiplier effects of urban density - capable of destabilizing firms whose machines have no intrinsic susceptibility to the disease, but which are dependent on humans who might be infected.

A second way in which the city is multi-scalar is in the geography of the environmental damages it produces (Girardet 2009; Rees 2006). Some of it is atmospheric; some of it internal to the built environment of the city, as might be the case with much sewage or disease; and some of it is in distant locations around the globe, as with deforestation. The case of ozone holes is one of the most serious instances of scale-up: the damage is produced at the micro-scale of cars, households, factories, and buildings, but its full impact becomes visible and measurable over the poles, where there are no cars and buildings.

A third way in which the city can be seen as multi-scalar is that its demand for resources can entail a geography of extraction and processing that spans the globe - though it does so in the form of a collection of confined individual sites, albeit sites distributed worldwide. (Girardet 2009; Rees 2006). This worldwide geography of extraction instantiates in particular and specific forms, such as furniture, jewellery, machinery and fuel inside the city. The city is one moment-the strategic moment-in this global geography of extraction, and it is different from that geography itself. A fourth way in which the city is multi-scalar is that it instantiates a variety of policy levels. It is one of the key sites where a very broad range of policies - supranational, national, regional and local - materialize in specific procedures, regulations, penalties, forms of compliance and types of violations (Satterthwaite et al. 2007; Low and Gleeson 2001; Etsy and Ivanova 2006). These specific outcomes are different from the actual policies, since they are designed and implemented at other levels of government.

It is also important to factor in the possibility of conflicts in and between spatial scales. Environmentalists can operate at broad spatial and temporal scales, observing the effects of local activities on macro-level conditions such as global warming, acid rain formation and global despoliation of the resource base. Environmentalists with a managerial approach often have to operate in very short time-frames and confined levels of operation, pursuing clean-ups and remedial measures for a particular locality - remedial measures that may do little to affect the broader condition involved. Indeed, they may diminish the sense of urgency about larger issues of resource consumption and thereby delay much-needed responses. On the other hand, economists or companies will tend to emphasize maximizing returns on a particular site over a specific period of time.


As I stated previously, it is not urbanization per se that is damaging, but rather the mode of urbanization, which extends to the adoption of environmentally harmful production processes in rural economies, such as the overuse of chemicals and deforestation, or air-conditioned buildings that worsen ozone holes, and other such interactions. Yet it is the complexity of cities that is also part of the solution.

The complexity and diversity of cities can help us engage the legal systems and profit motives that underlie and enable many of the environmentally damaging aspects of our societies. The question of urban sustainability cannot be reduced to modest interventions that leave major urban systems untouched; further, the actual features of urban systems vary across countries, and across cities within countries. While for some environmental issues, such as protecting the habitat of an endangered species, we can make considerable advances simply by acting on scientific knowledge, such is not the case when dealing with cities, or with society at large. Non-scientific elements are a crucial part of the picture: questions of power, poverty and inequality, ideology and cultural preferences, are all part of the question and the answer.

The spaces where environmental damage takes place often differ from the sites where responsibility for the damage lies - such as the headquarters of mining corporations - and where accountability should be demanded. A crucial issue is the massive worldwide investment promoting large projects that damage the environment. Deforestation, mining, and construction of large dams are perhaps among the best-known cases. The scale and the increasingly global and private rather than public-sector character of these investments suggest that citizens, governments and non-governmental organizations all lack the power to alter these investment patterns or influence their implementation.

However, particular kinds of cities that I call "global cities" should actually be seen as structural platforms for acting on and contesting irresponsible and powerful corporate actors (Sassen 2005; 2001). This is because the geography of economic globalization is strategic, especially when it comes to managing, coordinating, servicing and financing global economic operations. According to two major studies (MasterCard 2008; AT Kearny 2008), about 75 cities worldwide contain almost all of the headquarters of globally operating firms. There are sites - the network of global cities - in this strategic geography where the density of economic transactions and top-level management functions come together and constitute a concentrated geography of global decision-making. We can also see it as a strategic geography for demanding accountability from major corporate headquarters about environmental damage. For instance, a firm may have hundreds of mines across the world, but its headquarters might be in one, or perhaps a few, global cities.

The global economic system is characterized by enormous concentration of power in a limited number of large multinational corporations and global financial markets; for precisely this reason, it also concentrates rather than disperses sites where accountability and the changing of investment criteria can be demanded. Engaging a company's headquarters is actually easier than engaging the thousands of mines and factories in often remote and militarized sites, or the millions of service outlets of such global firms. Direct engagement with the headquarters of global firms is facilitated by the recognition among consumers, politicians and the media of an environmental crisis. Certainly, dealing with the headquarters of large firms leaves out millions of independent small local firms responsible for much environmental damage, but these are more likely to be controllable through national regulations and local activism.


Today the city is a strategic space for the direct and often brutal encounter between forces that are enormously destructive of the environment and of increasingly acute needs for environmental viability. This points to two critical dimensions. One is that urban governance must correspond with the development of environmentally sustainable urbanization. Secondly, this correspondence should maximize recognition of the multiple ecologies in cities and nature, respectively. Each point in these ecologies should be a bridge articulating the city and the environment.

Diverse empirical conditions both push towards and enable this complex articulation between cities' and nature's ecologies. For instance, most international and national environmental standards will also have to be implemented and enforced in cities, in addition to being enforced at national and international levels. This is partly because cities incorporate a large share of all environmentally destructive processes, including many that are not exclusively urban, and partly because the multi-scalar character of cities entails incorporation of national and global processes. The obverse of this specificity is that each city's mix of elements has a certain particularity - as does its mode of insertion within local and regional ecosystems. Out of this particularity comes place-based knowledge, which can then be scaled up and contribute to the understanding of national and global conditions.

All of this matters because it is now urgent to make cities and urbanization part of the solution: we need to use and build upon those features of cities that can re-orient the material and organizational ecologies of cities towards positive interactions with nature's ecologies. These interactions, and the diversity of domains they cover, are themselves an emergent socio-ecological system that bridges the city's and nature's ecologies. Part of the effort is to maximize the chances of positive environmental outcomes. Specific features of cities that may help include economies of scale, density and the associated potential for more efficient resource use, and, important but often neglected, dense networks of communication that can facilitate environmentally sound practices in cities. More analytically, insofar as cities are constituted through various processes that produce space, time, place and nature, cities also contain the transformative possibilities embedded in these same processes. For example, the temporal dimension becomes critical in environmentally sound initiatives: thus, ecological economics helps us recognize the efficient and value-adding character of the longer temporal frames of environmentally sound criteria. Conventional market criteria, with their ever-shorter temporal evaluation frames, might characterize much of this as inefficient or value destroying.

A city is a microcosm of the complex mix of variables we need to factor into our programs of change. Urban systems entail systems of social relations that support the current politico-economic organization, systems which we will have to dismantle partially or wholly in some cases. Cities are complex systems in their geographies of consumption and of waste-production: this complexity also makes them crucial for producing solutions. Some of the geographies for sound environmental action in cities will also operate worldwide. The network of global cities described earlier becomes a space at the global scale, not only for managing current investments, but also potentially for re-engineering environmentally destructive global capital investments into more responsible ones. It contains the sites of power of some of the most destructive actors, but potentially also the sites for demanding accountability of these actors. The scale of the network is different from the scale of the individual cities constituting this network. The circular logic that environmentalists want to introduce in the functioning of cities, i.e. maximum re-use of outputs to minimize waste, will entail spatial circuits that operate at different scales. Some will be internal to households, others will be citywide, and yet others will go beyond the city and run through sites around the globe.


Many of the biophysical stocks, flows and functions that we use are difficult to quantify and price through conventional understandings of markets, and others are simply invisible to conventional analysis: these are the issues taken up by ecological economists, beginning with the work of Rees (1992; 2006), Schulze (1994), Daly (1977), Daly and Farley (2003), among others. In contrast with neoclassical economics, ecological economics seeks to move away from models of infinite economic growth that separate the economy from the environment and move towards a model of sustainable growth that integrates social, built, natural and human capital components (Gund Institute 2009). Ecological economics rejects the belief that economic growth alone can lead to development. It seeks to incorporate measures of quality of life and environmental sustainability alongside GDP in assessing how development contributes to human well-being; it rejects the idea that new technologies can overcome all limits to growth, instead suggesting that there are real, insurmountable environmental limits to growth; and it emphasizes allocative efficiency over market efficiency (see Gund Institute 2009).One of the key propositions of ecological economics is that humans derive benefits from the ecosystem and from ecological processes. The value of these benefits - referred to as ecological or ecosystem services (ES) - is recognized and factored into ecological economic models as a non-marketed wealth underpinning marketed economic wealth (Porter et al. 2009). Ecological services include food (including agriculture), water, flood and disease control, recreational and spiritual benefits, and the cycling of nutrients that maintains conditions for life on earth. To measure economic development in terms of "real, sustainable well-being" instead of market growth alone (GDP), one needs to measure nonmarketable contributions to human well-being, such as those from nature, social relationships, health and education (Beddoe et al. 2009). In order to account for non-marketable contributions to human well-being, ecological economists have suggested alternative measures of development. Another key proposition of ecological economics is that there are limits to infinite growth. Whereas neoclassical economics assumes technological solutions to environmental limits, ecological economics sees these limits as real and ultimately insurmountable. Rather than increasing quantities of growth, then, ecological economists have suggested increasing qualitative improvements to generate greater economic welfare from fewer resource inputs -- in other words, increasing efficiency (Beddoe et al. 2009).