the new geography of contemporary urbanization and the environment

EG35CH07-Seto ARI 18 September 2010 7:9

The New Geography ofContemporary Urbanizationand the EnvironmentKaren C. Seto,1 Roberto Sanchez-Rodrıguez,2

and Michail Fragkias3

1School of Forestry and Environmental Studies, Yale University, New Haven, Connecticut06511; email: [email protected] of Environmental Sciences, University of California, Riverside,California 92521; email: [email protected] and Global Environmental Change Project, International HumanDimensions Program on Global Environmental Change, Global Institute of Sustainability,Arizona State University, Tempe, Arizona 85287; email: [email protected]

Annu. Rev. Environ. Resour. 2010. 35:167–94

First published online as a Review in Advance onAugust 13, 2010

The Annual Review of Environment and Resourcesis online at environ.annualreviews.org

This article’s doi:10.1146/annurev-environ-100809-125336

Copyright c© 2010 by Annual Reviews.All rights reserved

1543-5938/10/1121-0167$20.00

Key Words

agglomeration, climate change, drivers of urbanization, urban formand function, governance and institutions, sustainability

Abstract

Contemporary urbanization differs from historical patterns of urbangrowth in terms of scale, rate, location, form, and function. This re-view discusses the characteristics of contemporary urbanization and theroles of urban planning, governance, agglomeration, and globalizationforces in driving and shaping the relationship between urbanizationand the environment. We highlight recent research on urbanizationand global change in the context of sustainability as well as opportu-nities for bundling urban development efforts, climate mitigation, andadaptation strategies to create synergies to transition to sustainability.We conclude with an analysis of global greenhouse gas emissions un-der different scenarios of future urbanization growth and discuss theirimplications.

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Urbanization:contemporaryurbanization includeschanges indemographics, landcover, and economicprocesses andcharacteristics of ageographic area

Urban area: ageographical areacontaining highpopulation andlarge-scaleinfrastructure density;encompasses conceptsof town, city,metropolitan area,megacity, megalopolis,and conurbation

Contents

1. INTRODUCTION . . . . . . . . . . . . . . . . 1682. CHARACTERISTICS OF

CONTEMPORARYURBANIZATION . . . . . . . . . . . . . . . . 1702.1. Changes in Scale . . . . . . . . . . . . . . . 1702.2. Changes in Rate . . . . . . . . . . . . . . . 1722.3. Changes in Location . . . . . . . . . . . 1732.4. Changes in Form . . . . . . . . . . . . . . 1762.5. Changes in Urban Life

and Urban Function . . . . . . . . . . . . 1783. DRIVERS OF CONTEMPORARY

URBANIZATION . . . . . . . . . . . . . . . . 1793.1. Footloose Global Capital . . . . . . . 1793.2. Governance . . . . . . . . . . . . . . . . . . . 1803.3. Institutions . . . . . . . . . . . . . . . . . . . . 1813.4. Agglomeration Forces . . . . . . . . . . 182

4. BUNDLING URBANIZATIONAND SUSTAINABILITY . . . . . . . . . 1834.1. Urbanization as a Trigger for

Sustainability Solutions . . . . . . . . . 1834.2. Urban Land-Use Planning . . . . . 1844.3. Can Rapid Urbanization Save

the Environment? . . . . . . . . . . . . . . . 1865. CONCLUSIONS AND

FUTURE DIRECTIONS . . . . . . . . . 187

1. INTRODUCTION

The geography of urbanization is rapidlychanging and in multiple dimensions. Thesechanges in the characteristics of contemporaryurbanization are fundamentally transformingthe relationship between cities and the globalenvironment. We have now entered the Cen-tury of the City, and urbanization will be adefining social, economic, and environmentalcharacteristic of the new centennial. While sci-entists agree that we are presently living in theera of the Anthropocene, the period in Earth’shistory when humans are altering the function-ing of the global environment, we propose theterm Astycene as a more accurate descriptionof the new urban era where “anthropos” is an

“astos,” a dweller of an urban area.1 The Cen-tury of the City presents both global environ-mental challenges and opportunities.

Urbanization creates the most human-dominated landscapes and drives local andregional environmental changes by trans-forming land cover, hydrological systems, andbiogeochemistry (1). Worldwide, urban ex-pansion is one of the primary drivers of habitatloss and alteration and of plant and animalspecies extinction (2, 3). Yet, the concentrationof people, resources, and economic activityalso presents opportunities for transitions tosustainability. High population densities andcompact urban design are required to supportwalkable neighborhoods and mass transitalternatives to the automobile. Compact urbandevelopment coupled with high residential andemployment densities can reduce energy con-sumption, vehicle miles traveled, and carbondioxide (CO2) emissions (4). Concentratedpopulations can also save land for agriculture,wildlife, and habitat by using less land forurban development. The trade-offs betweenenvironmental challenges and opportunitieswill depend in large part on how and whereurban areas expand, urban lifestyles, andconsumption patterns as well as the abilityof institutions and governance structures toaddress adequately these challenges.

Over the past two decades, there has beenan increase in the number of studies concern-ing the interactions between urbanization andglobal environmental change. There is a grow-ing community of researchers that studies theeffects of urbanization on the global environ-ment and the impacts of global change on urbanareas. These bidirectional interactions betweenurbanization and global change are a core com-ponent of the Urbanization and Global Envi-ronmental Change project of the InternationalHuman Dimensions Program on Global Envi-ronmental Change (5).

The environmental literature of the 1960sthrough the 1980s predominantly viewed

1The term is derived from the Greek words αστυ (asty, city,town) and καινoς (cene, new).

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urbanization and cities as environmentalills, but recent research is revealing a morecomplex relationship between urbanizationand the environment. Some suggest thaturbanization—through the associated eco-nomic development and rises in income—willincrease environmental awareness, protection,and quality; others point to problems with thishypothesis by focusing on the increase in con-sumption of resources and energy associatedwith urbanization, irreversible environmentaldegradation, or even the existence of pollutionhavens (6, 7). This debate about the relationshipbetween economic development and the envi-ronment is decades old, and recent empiricalwork suggests that factors other than income,such as governance, regulation, and technologydiffusion, may drive environmental quality(8–11). In short, past literature is inconclusiveof whether and how urbanization has a clearpositive or negative effect on the environment.

Much has been written about the demo-graphic characteristics of contemporary ur-banization at regional and global scales (12,13). Less has been written about the inter-actions between the social and the physi-cal dimensions of urbanization and the bidi-rectional feedback between urbanization andglobal change. The study of the physical com-ponent of urbanization—the conversion of landcover to urban uses—is not well understood,especially at global scales. Most of our under-standing of urbanization as a land change pro-cess is based on individual case studies of citiesor metro regions (14). What is becoming clearfrom these case studies is that there are sig-nificant differences in urbanization processesamong regions and countries, and even withincountries; urbanization is not a homogeneousprocess. Identifying these differences, as wellas their commonalities, is critical for sustain-ability because different forms of urbanizationhave different impacts on the local and globalenvironment. The spatial configuration of ur-ban land use, urban processes, urban form, andthe rate and scale of urbanization determines

Sustainability:meeting the needs ofthe presentgenerations withoutcompromising thecapacity of futuregenerations to meettheir needs

Institutions: formalrules and informalconstraints that affectstrongly or weakly,directly and indirectlyeveryday behavior andchoices in market andnonmarket settings

Governance: theprocess of governing,such as top-downadministrationthrough national levelor bottom-up fromcommunityorganizations

many of the interactions between urban areasand the environment.

The aims of this review are to discuss the keycharacteristics of contemporary urbanization,with an emphasis on urban land-use change,and to identify their drivers. We draw on theplanning, urbanization, and climate change lit-eratures and make recommendations for win-win strategies for bundling rapid urbanizationand sustainability. In Section 2, we describe themajor characteristics of contemporary urban-ization. The purpose is to identify the multipleand concurrent changes in urban areas to de-velop a more complete understanding of the dy-namics of urbanization trends and their impli-cations for the environment. The effects of ur-banization on hydrologic systems, biodiversity,climate change, and biogeochemical cycles arenot discussed in this review. Rather, we focusour discussion on the impacts of urbanizationon land cover conversion. Section 3 looks at thedrivers of urban growth and specifically focuseson nondemographic factors. We view a discus-sion of nondemographic drivers of urbanizationas important for three reasons. First, the nonde-mographic drivers of urbanization play a signifi-cant role in determining demographic changes,and yet the connections are often not explic-itly discussed. Second, although their effects arelocally specific, nondemographic drivers oper-ate at multiple spatial scales and are not con-tained within an urban area. Third, these non-demographic drivers interact and can amplifytheir individual impacts on urbanization pro-cesses. Section 4 describes the opportunitiesfor bundling urban development initiatives andclimate mitigation and adaptation strategies tocreate synergies to transition to sustainability.We focus on urban land-use planning and waysin which it can foster urban forms that are moresustainable. We conclude Section 4 with ananalysis of greenhouse gas emissions under dif-ferent scenarios of urbanization and populationgrowth over the next 40 years. Finally, Section5 summarizes the findings of this synthesis andsuggests directions for future research.

www.annualreviews.org • Rapid Urbanization and the Environment 169

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City: a subset of anurban area, defined bypolitical administrativeboundaries

Agglomeration: thegeographicconcentration ofeconomic activity thatis observed acrossscales—the formationof urban centers,industrial clusters,hierarchical systems ofcities

2. CHARACTERISTICS OFCONTEMPORARYURBANIZATION

Twenty years ago, Kates et al. (15) wrote thatwe live in a special period in history, call-ing it the “Great Transformation,” one where“the scales, rates, and kinds of environmentalchanges have been fundamentally altered as hu-manity has passed through an era of rapid pop-ulation growth . . . .” We are now in a secondgreat transformation. Humanity crossed a mile-stone in 2008 when the global urban popula-tion exceeded the rural population for the firsttime in history. Short of major health epidemicsand natural hazards that affect large populationcenters, a growing proportion of world popula-tion will live in urban areas for the foreseeablefuture.

This trend is a departure from most ofhuman history when populations were mainlyrural and lived in smaller urban settlements.This new era of urbanization—as both ademographic and land change process—hascharacteristics that differentiate it from otherperiods in history. First, the scale of urban-ization is extraordinary; cities are bigger thanat any other time in terms of their physicalextents, population sizes, economic impor-tance, and environmental impacts. Second,the rate at which populations and land coverare becoming urban is faster than at anyother time in history. Third, the location ofurbanization is changing; the urban transitionin Europe and South America occurred in the1950s through the 1970s. Urban growth in thecoming decades will take place primarily in Asiaand Africa and expand into agricultural lands,forests, and other natural land covers. Fourth,the form of urban settlements is changing.Urban areas have historically been compactand concentrated populations. Urban areasare now increasingly expansive and peri-urbanwith significant differences between developedand developing countries. Fifth, urban functionis increasingly specialized, and this, in turn,has differentiated its effects on the urban laborforce, urban lifestyles, and the environment.

There is perhaps a sixth characteristicof contemporary urbanization: The afore-mentioned trends interact and amplify theirindividual effects. These characteristics areinterrelated, and the processes that drive themco-evolve. Individually, these characteristicssuggest a significant break from periods of rapidurbanization in the past; together, they repre-sent a profoundly new era of urbanization.

2.1. Changes in Scale

Some of the most defining attributes of the newera of rapid urbanization are the absolute sizeof urban areas in terms of their increased popu-lation, their physical extent, and the number ofurban areas. For individual cities, urban popu-lations have reached incomparable scales.

At the start of the 1800s when the worldpopulation was around one billion people, Bei-jing was the only city with a population of onemillion or greater. One hundred years later, atthe turn of the twentieth century, there were 16cities with populations of one million or greater.Forward another hundred years to 2000, andthere were 378 cities with populations of greaterthan one million (16). In India alone, there arenow 40 cities with populations of 1 million; inChina, there are more than 100. By 2025, therewill be about 600 cities of one million or moreworldwide (Table 1).

Not only are there more urban settlements,but there are more very large urban agglomer-ations. In 1900, there were no cities with a pop-ulation of 10 million. By 1950, the New YorkCity metropolitan area became the first urbanarea to reach a population of 10 million (16).Tokyo was the first city to have a population of10 million in 1962. Today there are 19 urbanagglomerations with populations of 10 millionor more, with Tokyo-Yokohama at the top ofthe list with a population of 35.7 million; thecity of Tokyo has 12.8 million people (16).

For years, it was assumed that urban ar-eas were less important in global change stud-ies because total global urban land cover wasa relatively small proportion of Earth’s terres-trial surface—less than 2% (17). Although there


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are estimates of urban population growth atnational and global scales, there is little un-derstanding of how urban land cover has orwill change as a result of urban populationgrowth. Satellite-based studies calculate urbanland cover at 3% to 5% of total land surface,but there remain significant uncertainties withmapping urban land cover and urban expan-sion at global scales (18). In particular, thereare greater variations in estimates of urban areafor Asia than other regions of the world (19).

Individual case studies reveal that urban ar-eas have reached a physical size unparalleled inhistory. The urban extent of Tokyo-Yokohamacovers 13,500 km2, an area that is bigger thanJamaica (11,000 km2). Massive urban land-usechange has occurred all around the world. In theNile Delta, approximately 3,000 km2 of landhave been converted to urban uses over a 30-year period from 1970 to 2000 (20). In PuertoRico, urban sprawl affects 40% of the island andone-quarter of the island’s prime agriculturalland (21). During a 10-year period from 1990to 2000, urban areas in China expanded by more8,100 km2, an area about the size of Puerto Rico(22).

2.2. Changes in Rate

A second characteristic of contemporary urban-ization is the rapidity with which urban popula-tions are growing and land cover is being con-verted to urban areas. High urbanization levelsare a relatively recent occurrence. It took all of

Table 2 Global urban population and time intervals for the additionof 1 billion urban residents

Year attained Global urban population Number of years1960 1 billion 5000+a

1986 2 billion 262003 3 billion 172018 4 billion 152031 5 billion 132044 6 billion 13

aThe longest history of urban population growth dates back to 3,000 BC (147). Thisanalysis extends an earlier study by Satterthwaite (23).

history until 1960 for the world urban popu-lation to reach one billion, but only 26 yearsto reach two billion (Table 2). Since then, thetime interval it takes to add an additional onebillion urban dwellers is decreasing, indicat-ing an increase in the rate of urban populationgrowth. In fewer than 100 years, the urban pop-ulation will grow from one billion to six billion.

Rapid urban population growth is a re-cent phenomenon. Levels of world urbaniza-tion from the first century until the middle ofthe nineteenth century ranged between 4% and7%, and rates of urban population growth wereextremely low. Since the 1950s, global magni-tudes and rates of urbanization have been as-tounding. At early stages of the urban tran-sition, where levels of urban population arelow, rapid urbanization depends on high annualrates of population change. The urban popula-tion rate of growth is slowing down globally(19). From 1950 to 2007, it averaged at 2.6%per year—an average that is expected to drop to1.8% between 2007 and 2025; at this rate, urbanpopulation would double in 38 years (16). Butas the national percentage of urban populationbecomes larger, high annual rates of urban pop-ulation growth are not required for high mag-nitudes of urban population change (Figure 1,see color insert). For example, across all worldregions, urban population annual growth ratesare highest closer to the 1950s and have steadilydeclined since then (Figure 1). But even withdeclining growth rates, the absolute magnitudesof increase of urban populations is at all timehighs. Figure 2 (see color insert) contrasts theurban population growth rates for India andChina with the proportion of urban populationin each country across time. For both coun-tries, the urban population growth rate rangedfrom about 2% to 5% between 1950 and 1970,with significant variability. Since the 1990s, thetrend is declining; circa 2010, these rates werebetween 2% and 3%. However, the propor-tion of the population that is urban is grow-ing in both countries. By 2050, more than 70%and 50% of the population in China and India,respectively, will be urban. In the future, ur-ban population growth rates are expected to be


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twice as high as the world’s population growthas a whole (16). Other analyses of the UN pop-ulation data have similarly concluded that therate and magnitude of urban population growthis unparalleled (12, 23).

As urban populations grow, urban land ex-pands upward or outward to accommodate thenew population. For most of history, the rateof urban land expansion was low, and the phys-ical extent of cities grew slowly. Walled citieswere common from the fifth to the sixteenthcentury in Europe and China, and these barri-ers served to contain the growth of the city aswell as physically separate the city from its en-virons (24, 25). For example, the circumferenceof Beijing was approximately 28.6 km for morethan 300 years from the mid-1200s throughthe mid-1500s (26). Contemporary cities havefew, if any, material boundaries, and many areexpanding unencumbered. Some have shownthat in parts of the United States and Europe,urban land area grows in proportion to ur-ban populations, and a scaling relationship ex-ists between the two (27, 28). Using data for108 cities from two satellite-based studies ofurban land expansion (29, 30), we found thatthe rate of urban land expansion to be fasterthan the rate of urban population expansionfor most cities, suggesting that these urban ar-eas are becoming more expansive than compact(Figure 3).

2.3. Changes in Location

Over most of the last 2,000 years, the world’slargest cities have primarily been in the East-ern Hemisphere (Table 3). Not until 1800did the first European city appear as one ofthe top five largest cities. From 1900 to 1950,the largest cities were located in Europe and theUnited States. In the new era of urbanization,the largest cities will be in Asia and SouthAmerica. Between 2007 and 2050, the world ur-ban population is expected to increase by morethan 3 billion. This scenario assumes a reduc-tion in fertility rates in developing countries;if fertility remains at current levels, then ur-ban populations may increase by as much as T

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5 billion over the next 40 years. The majority ofthis growth will occur in Africa and Asia, wherecurrent urbanization levels are low at 40% and45%, but the increased scale of urbanizationwill be most extraordinary in China and India.

Over the next two decades, the urban pop-ulation in China is expected to exceed one bil-lion, an increase of 400 million, and result in thecreation of at least 30 cities of one million (16).During this same period, the total populationof India is projected to surpass that of China,with its urban population nearly doubling fromtoday’s 350 million to 611 million and with anaddition of 26 cities of one million. The com-bined urban population growth in China andIndia is expected to be more than 700 millionover the coming two decades. Although demog-raphers warn of the uncertainties around thesenational level population forecasts (12) and citysize projections (31), the current and expectedurban transitions in China and India representthe largest scale of urbanization the world hasever experienced. Put into a global context, by2030, nearly one of every three of the world’surban residents will reside in either China orIndia (Figure 4, see color insert).

Historically, urban settlements developednear fertile agricultural lands and water bod-ies. Contemporary urban settlements are nowin the far corners of Earth and have transformedevery type of ecosystem. The global natural re-source supply and distribution chains have en-abled large settlements to develop in arid en-vironments and other resource-constrained re-gions. The rise and extensive development ofcities in the Middle East over the past 20 yearshas been enabled by the development of de-salinization plants; in 2005, 70 of the 100 largestdesalinization plants proposed, in construction,or in operation in the world were in the Mid-dle East (32). In 1975, the population of Dubaiwas only 183,000; by 2009, its population hadincreased ninefold to over 1.7 million.

Whereas in 1950 the geographic distribu-tion of large cities was more evenly distributedworldwide, a majority of the largest cities—andmore than half of the world’s cities with popu-lations of 500,000 and greater—will be located

in Asia (Table 1). The changing geography ofurbanization is expected to have varying im-pacts on ecosystems and land cover. Urban-ization may result in households climbing upthe “energy ladder” and switching from fuel-wood to modern fuel sources, thereby reducingpressure on forest cover (33). Others suggestthat urbanization will reduce pressure on forestsowing to a shrinking rural population and theextent to which these populations cause defor-estation (34). Irrespective of rural consumptionpatterns, the physical expansion of urban areaswill transform land cover and habitat. The ur-ban transformation of Singapore has resultedin a 95% loss of habitat and up to 87% ex-tinction rates for various forest taxa (35). To-day, one-quarter of the world’s protected areasare within 17 km of a city with a populationof 50,000; by 2030, the distance will decline to15 km (2). In the United States, housing de-velopment growth rates near protected areasare higher than national averages and threatentheir conservation value (36). Depending onurban population densities and the rate of ur-ban land expansion, an additional 3 billion ur-ban dwellers may require from 400,000 km2 to1,429,000 km2 of new urban land, equal to anarea four times the size of Germany (37).

2.4. Changes in Form

Although most studies of urbanization and theenvironment have focused on defining the rateand scale of urban land change, fewer studieshave evaluated the changing form of urban ar-eas. Yet, urban form—or urban morphology—is central to the impact of urbanization on theenvironment. Urban form has been studied formore than a century within the fields of ur-ban planning, economics, geography, and so-ciology, which have developed the foundationsabout spatial land-use theory and models (38,39). Since the 1960s, work on urban growthand morphology have been an important sub-ject of interest—not only for geographers andeconomists (40–42)—but also for natural scien-tists and physicists (43).


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The past 125 years have thus resulted in awealth of knowledge on the spatial form of ur-ban systems. We now view the spatial configu-ration of urban areas as a path-dependent pro-cess that is a reflection of past decisions as wellas a manifestation of current socioeconomicand political processes; some of these includeplanning, transportation costs, agglomerationeconomies, and market prices. The interactionbetween these processes and the landscape isimportant in shaping urban form in developedand developing countries. However, poverty,social inequality, and marginalization in devel-oping countries create differentiated outcomesin urban form. This is a relevant issue giventhe rapid pace of urbanization in those coun-tries and the high concentration of future pop-ulation growth expected in those settlements.Still, we also know that urban systems are com-plex adaptive systems, hierarchically structuredat several levels. Urban systems follow powerand scaling laws in their distribution of pop-ulations and area extents. We observe scalinglaws at different geographical scales, from thenational system of cities (44) to urban clusterswithin metropolitan areas (45, 46).

Up until recently, urban land-use changewas primarily explored through one-dimensional measures of area extent orrate of land cover change. However, it hasbeen shown that aggregate measures of urbanextent and growth rates do not quantify criticalcomponents of the urban land change process,such as the degree to which urban expansionis compact or leapfrogging (47). Quantifyingand describing changes in urban land-usepatterns beyond its extent and cumulativegrowth rates requires an explicit look at thelandscape mosaic. Increasingly, urban land-usechange studies use spatial pattern metrics thatoriginate from the field of landscape ecology(48–50). Many of the indices that have beendeveloped to characterize the complexity,shape, and configuration of landscapes (51)are particularly useful to the study of urbanmorphology.

Studies of urban morphology and rates of ur-ban expansion show that contemporary urban-

ization is increasingly disperse and expansive(29, 52). For centuries, cities were characterizedby compact living. Through historical data, weknow that the U.S. system of cities progressedfrom small, compact, dense, coastal develop-ments during the colonial era to larger, com-pact, dense, and further inland developmentby the middle of the twentieth century. SinceWorld War II, urban densities in the UnitedStates have dropped as populations moved fur-ther away from the urban centers, and urbangrowth patterns have become more expansive,which, in turn, has lead to high-consumptionlevels of land, water, and fossil fuels and ad-versely impacted ecosystem services (53, 54).Although these automobile-centric patterns oflow-density suburban development—what Le-ichenko & Solecki call “consumption land-scapes” (55)—have been observed in the UnitedStates for more than half a century, they are arelatively new, but increasingly common, phe-nomenon around the world. Empirical studieshave documented the rise in this type of expan-sive development in many countries, includingIndia (56), China (57), Mexico (58), Brazil (59),Canada (60), and Australia (61).

In addition to widespread suburbanization,which is dominated by single-family residen-tial development, there is also an increase inthe phenomenon of peri-urbanization (62, 63).The peri-urban interface refers to spatially andstructurally dynamic transition zones whereland use, populations, and activities are nei-ther fully urban nor rural. Although it is of-ten assumed that populations and economic ac-tivities can be sharply divided between urban(industrial) and rural (agricultural), peri-urbanhouseholds may be multispatial, with some fam-ily members living in rural areas but not em-ployed in agricultural activities and others liv-ing in urban areas but engaged in agriculture(64). As such, peri-urban areas are hybrid land-scapes: a juxtaposition of traditional and ruralwith modern and urban. In these areas, thereis an intense interaction between rural and ur-ban economies and lifestyles. Peri-urbanizationis usually initiated by an influx of nonlocal cap-ital in industries or housing development and


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can take place as far as hundreds of kilome-ters from the urban core. Peri-urbanization isoccurring throughout the world, but some re-searchers suggest that it is the dominant form ofurbanization in East Asia, and this style of ur-ban development presents new challenges forplanning and governance (65, 66).

2.5. Changes in Urban Lifeand Urban Function

The aforementioned changes in the physicaland demographic characteristics of contempo-rary urbanization are paralleled by significantchanges in urban function and urban life.The term urban primacy refers to the degreeto which a city’s population and economicfunction dominates other cities in a country. Aprimate city is the population, economic, andcultural hub of a country. Bangkok is an excel-lent example of a primate city: Its population of6.9 million is 25 times that of the second largestcity, and its economy generates nearly half ofthe country’s gross domestic product (GDP).Buenos Aires is another example of extremeurban primacy: It is home to one-third ofArgentina’s total population. According to em-pirical evidence, the degree to which a country’spopulational and economic resources is concen-trated in a single city is a function of domesticpolitical stability and the country’s participationin international trade (67). However, histor-ical concentration of political and economicpower in countries’ capital cities continues tostrengthen urban primacy in some major cities.It is equally important to consider the functionof urban areas in the subnational geographicspace. Urban areas are economic, social,cultural, and political centers that also serve ashubs for regional development. They interactdynamically with rural and peri-urban areasthrough the exchange of goods and services,and they create stability to regional structures.A third level of urban function worth consid-ering is intraurban. The dynamic interactionsof economic, social, and cultural processeswithin the urban space are key determinants

of the scale, rate, and geographic patterns ofurbanization.

In terms of urban life, there are clear in-dications that family dynamics are changingin this new era of urbanization. Family sizeis shrinking, and in cultures where multigen-erational housing was the norm, two-personhouseholds are now more common. There isalso a stronger social and economic link be-tween the urban and the rural. This is in partdue to the peri-urbanization process wherebysome family members reside in the city and oth-ers in the countryside. Nevertheless, the point isthat the division between urban and rural is lessdistinct today. Another change in urban livingis the embrace of Western styles of architec-ture and urbanization, which are resource in-tensive and often not adapted to local climates.The North American suburb has gone global,and car-dependent urban developments are in-creasingly the norm. These patterns of sprawleddevelopment have been associated with increas-ing social segregation and reduced communityparticipation, less social involvement, and a dis-ruption of community “boundedness” (68). Theinternational debate on climate change createsa useful framework to consider the real impactof the current Western model of consumptionand lifestyle exported through globalization—even to the most remote regions of the world.

As more world regions move further alongtheir urban transition, Western-style diets arebeing adopted globally. Asian diets have al-ready shifted away from staples and are movingtoward meat and dairy products, vegetables,fruit, fats, and oils (69). It is theorized thatglobalization (through increased trade andflow of products, services, and information),mass-media marketing, the prevalence ofmultinational food corporations in food supplychains, and the increasingly close connectionsin the lives of urbanites are the main forcesdriving the phenomenon (70). Obesity is con-sidered an emerging epidemic in the developingworld, and concerns regarding additional ad-verse health effects and the health inequities ofurban diets in developing countries have startedto materialize (71, 72). Recent research has


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documented the impact of the built environ-ment on lifestyles and suggests that the urbanform can reduce incentives and possibilitiesfor physical exercise within urban areas (73).The research also shows a strong relationshipbetween the mix of land uses and obesity (74).

We know that, viewed as a whole, urban ar-eas show significantly higher levels of wealthbecause of higher productivity levels. However,a big challenge in urban research is the lack ofmeasures of GDP growth at the urban scale. Itis estimated that 30% of national GDP in theUnited Kingdom, Sweden, Japan, and France isaccounted for by London, Stockholm, Tokyo,and Paris, respectively (75). Globally, metro ar-eas drive their national economics, but there aresignificant disparities in the GDP per capita be-tween and within the world’s urban areas (75,76). There is even a bigger disparity betweenthe wealthy and the poor in cities, and this dis-parity is exacerbated by the scale and rapidity ofchange. Economic development and improve-ments in well-being are only part of the urban-ization story: Worldwide, more than 900 mil-lion people live in informal settlements, withmost living under life- and health-threateningconditions (77, 78). Put another way, approxi-mately one out of three urban dwellers world-wide lives in slum conditions, and this ratiois expected to increase in the future. In lightof their importance locally and regionally, andconsidering their size globally, the discussion ofsustainability needs to incorporate approachesthat include and consider informal settlements.

3. DRIVERS OF CONTEMPORARYURBANIZATION

Interacting processes that operate acrossmultiple spatial scales are driving the rapidity,scale, and geographic reach of contemporaryurbanization. These drivers are not limited tothe urban boundary. Our understanding of thedrivers of urban land expansion has developedsignificantly beyond population growth anddemographic trends. In this discussion, wefocus on three nondemographic drivers thatinteract, amplify changes in urban areas, and

are transforming contemporary patterns ofurbanization: footloose international capital,governance and institutional structures, andagglomeration forces.

3.1. Footloose Global Capital

International capital is shaping the expan-sion of urban areas in three ways. First, in-ternational real estate developers and prop-erty management firms have become a ma-jor presence, contributing to the developmentof high-rent industrial and residential facili-ties, built in a geographically indistinguishable“global modern” style that can be found any-where from the San Francisco Bay Area toBengaluru (79, 80). Second, the space, in-frastructure, and human resource demands ofmultinational firms—particularly technologyand science industries—have required the con-struction of facilities with superior physical in-frastructure and particular amenities (81, 82).These may include broadband Internet, un-interrupted electrical power, water, air condi-tioning and computer and telecommunicationsroom cooling facilities, and security. Third,the influx of international capital has changedthe landscape of consumption in urban areasaround the world, as educated workers flowinto the city after returning from extended em-ployment opportunities in the United Statesand Europe, and as rising worker incomes in-crease the demand for higher-end, and oftenimported, consumer goods and services (83).The influx of international capital has pro-duced dispersed urban growth as well as un-planned and uncoordinated urban expansion incities around the world from Warsaw (84) toShanghai (85).

The impact of international capital on lo-cal development and economies is not alwayspositive. For example, the rapid expansion ofindustries in urban and peri-urban areas haslead to the creation of slums to accommodateworkers of those industries. Injections of for-eign capital are also driving changes in housingand lifestyles that conflict with traditional waysof living. Large tracts of land are developed as


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special economic, export, and industrial zoneswith the purpose of developing domestic indus-tries and attracting developers and internationalcorporations. India has 101 special economiczones in operation, and nearly 600 more havebeen approved (86). In China, it is estimatedthat 6% of the country’s arable land was con-verted to development zones between 1986 and1995 (87). Thus, rapid urbanization in many re-gions is at the expense of prime farmland, re-sulting in governments buying or leasing agri-cultural land abroad—what some call a “globalland grab” (88).

3.2. Governance

Urban governance has moved away from a ver-tical and hierarchical system of government to-ward a horizontal network-oriented frameworkwith greater emphasis on democratic participa-tion and decentralization. This has allowed forthe participation of new actors from the pri-vate and social sectors, which, in turn, is ex-pected to lead to new cooperation processes andthe establishment of new negotiation systems(89). There are common characteristics in thenew urban governance and institutional struc-tures but also regional differences. One com-mon element of new urban governance thataffects the path and rate of urbanizationthroughout regions is the effort from national,state, and provincial governments to transfermanagement responsibilities for public servicesto local governments without transferring ad-equate financial resources to take over thoseresponsibilities. Some argue that the increasedparticipation in urban governance from the pri-vate sector and civil society reduces governmentresponsibility for and accountability of urbandevelopment, particularly in the supply of pub-lic services (90, 91).

Since the 1990s, new processes of decentral-ization and regionalization have affected the in-stitutional landscape in the European Union(EU): the wave of territorial reorganizationand major transformations of European states;a new division of labor between states, lo-cal and regional authorities, and decentraliza-

tion; and regionalization or federalization (91).Urban areas are important elements in address-ing those transformations and the challengesof globalization. Urban areas gained increasedautonomy with regard to their national institu-tional frameworks, and the EU promoted sus-tainable urban development and the implemen-tation of the partnership principle, seeking suc-cessful urban governance (92). The reforms ofurban institutions were aimed at optimizing thedelivery of public services, at generating a col-lective dynamic at the urban level, and at cre-ating projects that would bring together a largenumber of local actors from diverse areas ofcivic society (90).

New urban governance regimes have haddifferent effects in other regions. Despite a tra-dition of seeking a broader participation ofcivil society, urban governance in North Amer-ica lacks the financial and institutional supportfrom national governments, and there is nosupranational institution similar to the EU. Ur-ban communities in the United States have di-verse, decentralized, and fragmented models ofdeveloping and financing urban infrastructureand public services. Urban policy makers arenow negotiating with neighboring communi-ties, competitive markets, and citizens in a frag-mented governance system (93). Urban areashave increasingly relied on state governmentsfor assistance in addressing major problems,and their revenue structure has increasinglybecome dependent on user fees and charges.There has been an explosion of public authori-ties and special districts since the late 1950s. Ur-ban areas have outsourced the provision of pub-lic services to authorities and special districtsthat operate separately from the municipal gov-ernment while simultaneously charging citizensfor these services; these include water and sewerservices, mass transit, bridges, tollways, floodcontrol and drainage, housing, and redevelop-ment (94). These new arrangements have fun-damentally changed the process of urbanizationby reducing the effectiveness of local planningand authorities in shaping urban development.

Another significant change in urban gov-ernance and institutions in the United States


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that has affected the pattern of urbanization isthe increase in the formation of “private gov-ernments” through homeowners’ associations(HOAs) during the past 35 years. The numberof people living in HOAs climbed from 2 mil-lion in 1970 to 58.8 million in 2007 (93). ManyHOAs have infrastructure responsibilities, buttheir capacity for integrated and coordinatedaction in a metropolitan area is severely limited.Thus, urban governance in the United States isconfronted by fragmented financial and policy-making systems, and the current models of ur-ban governance have dramatic consequences onthe physical expansion of urban areas (75). Un-fortunately, most of the discussion about urbansprawl in the United States has been detachedfrom the discussion of urban governance. Thechallenge for urban communities is that thefragmented structure of urban governance is anobstacle to creating consensus among a diversearray of actors needed to integrate plans for ur-ban sustainability.

In developing countries, urban governancestrongly relates to problems of political processand limited human, technical, and financialresources to direct urban development. Thechanges, driven by international capital, arebeing played out in the context of the de-veloping countries’ weak regional planninginfrastructures, which historically have focusedon their central cities (95). Changes in urbangovernance and institutions, combined withthe relaxation of economic regulations, areenabling international capital, institutions,and actors to accelerate the process of plan-ning privatization and economic segregation.Foreign capital is effectively trumping publicregional planning owing to changes in urbangovernance and is accelerating the rate of urbangrowth while changing the basic structureand function of urban areas. The results arenew urban artifacts, such as shopping malls,large commercial spaces, industrial estates, andgated communities (96).

Although gated and restricted access com-munities have long been a presence in industri-alized cities, they have emerged as a commonform of urbanization in developing-country

cities and created with them new forms of socialexclusion (97, 98). Conflicts are also arising inperi-urban areas because of competing interestsbetween international firms and local develop-ment. National or state governments identifyland for international investment and urban de-velopment but often exclude local municipali-ties in the decision-making process and expectthem to maintain the projects (84).

The lack of inclusive urban governancehas aggravated the urbanization process incountries characterized by social and physicalmarginalization of large numbers of urban in-habitants, poverty, and environmental degra-dation, with sharp contrasts between the for-mal and informal urban space, the rich and thepoor, the legal and the illegal. Yet, despite thedire situation of the poor and the severe limi-tations of urban governance, some of the mostinteresting and comprehensive initiatives of ur-ban governance emerge from countries, such asBrazil and Thailand (99–101).

3.3. Institutions

Closely related to the issue of urban governanceare the roles of institutions that define thescale, rate, and form of urbanization. Here wehighlight three major—and often interacting—institutions that are central to shaping thecontemporary urbanization process: the real es-tate market, spatial planning, and the voluntarysector. The relations of power among urbanactors significantly influence the urban spaceresulting from those interactions. For example,local real estate markets have traditionally beena major institution in defining urban land-usepatterns. Globalization has transformed thecommercial property market from a local toan international industry (102). In Mexico, theinflux of transnational corporations has createdinefficiencies in the real estate market andintense competition for urban land and urbanservices (103). These market inefficiencies havelead to conflicts and contradictions in accessto urban land and public services, therebycreating fragmented urbanization processesand the rapid spread of informal settlements inMexican border communities.


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An important driver of the rate, scale, andpattern of urbanization are land-use plans de-veloped by local authorities. Irrespective ofnomenclature—comprehensive plans, masterplans, general land-use plans, spatial plans, orregional plans—the primary purpose is thesame: to determine and coordinate the loca-tion and arrangement of the built environment,infrastructure, and natural resources. Land-useplanning tools, such as zoning, attempt to con-trol the degree to which neighborhoods are sin-gle use (residential, commercial, or industrial),define residential and commercial density, af-fect transportation infrastructure, and encour-age the conservation of green space.

Despite the potential power of spatial plan-ning to direct the scale, rate, and form of ur-banization, it has been incapable of controllingand orienting urban growth (104). More than35 years ago, Blair (105) highlighted the defi-ciencies in urban planning approaches. Morerecent research questions the assumption thaturban planning can impose order to the in-herent complexity of the urbanization process(106). In the United States, urban plans havefailed despite more than a century of progres-sive urban planning (107), and urban planning isincreasingly decentralized and privatized (108).In developing countries, international masterplanning consultancies are emerging as power-ful institutions that shape the new urban land-scape. They are brought in at the behest ofeither local or national authorities and oftenthrough international competition. These con-sultancies are planning, designing, and buildingthe new urban landscape around the world, withlocal planning institutions playing a relativelyminor role.

Research over the past decade has alsodocumented an increasing role of the voluntarysector and nongovernmental organizations inshaping the urban landscape, especially in help-ing urban communities mobilize resources toimprove public services and social well-being.The role of the voluntary sector is promoted byinternational organizations, such as the WorldBank and UN-Habitat, as an important steptoward affecting urban governance and the

form and scale of urbanization. In Bangkok,nongovernmental organizations (NGOs) havefacilitated the development of communitycapacity to deal with environmental and urbanproblems in slums (101). NGOs also play animportant role in reconciling informal andformal institutions addressing urban landmanagement in developing countries (109).

3.4. Agglomeration Forces

The classic conceptualization of an urban areais that of a featureless plain, where land usesaround a central business district are the re-sult of the tension between declining land pricegradients and increasing transportation costs(39). Our understanding of urban growth dy-namics has increased considerably, in particu-lar over the past 30 years, and we now havea more complex view of the factors that causecities to expand spatially. One of the emergingthemes is agglomeration forces, that is, factorsthat drive the geographic concentration of eco-nomic activity across different scales. Agglom-eration manifests itself as clustering in neigh-borhoods (at the smallest scale), city formations(at a medium scale), and the core-peripherystructure of nations (at the largest scale). Thisnew economic geography distinguishes forcesthat disperse economic activity, such as landrents and immobile factors (e.g., land and natu-ral resource), from forces that concentrate eco-nomic activity, such as forward and backwardproduction linkages and labor markets (110).Important drivers of the urban growth of citiesare economic activities that are in their geo-graphic proximity and also national and inter-national trade connections.

Many agglomeration drivers have been pro-posed and theorized. These include commu-nication externalities, spatial competition, andincreasing returns to scale in economic activ-ity (111); urbanization (diversity in productionactivities) and localization (specialization in asingle sector) economies (112); spatial competi-tion through individual firm location decisions,large land developer decisions, and the avail-ability of infrastructure (113, 114); local levels


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of creativity and innovation (115); and the pres-ence of multiple central business districts (116).There is still much to study about agglomera-tion processes, but it is already clear that clus-tering is a globally dominant trend that occursat various scales (117).

In their evaluation of the empirical litera-ture of the past 30 years, Rosenthal & Strange(118) find evidence of economic agglomera-tion forces of labor market pooling, input shar-ing, and knowledge spillovers. Furthermore,they also find that natural advantage, homemarket effects, consumption opportunities, andrent seeking all contribute to agglomeration.Although agglomeration forces are theorizedto be at play in all urban areas, several exam-ples elucidate the concepts. The presence ofagglomeration forces at multiple scales can beobserved in cases such as the regional develop-ment of the Manufacturing Belt (or Rust Belt)in the northeastern United States beginning inthe nineteenth century, Italy’s industrial north,and recently the Pearl River Delta in China; atthe lower scale, agglomeration forces drove theformation of clusters like Route 128 in Bostonand the Silicon Valley in Santa Clara County,California, and, more recently, in Bangalore,India (79).

Agglomeration across scales is now a domi-nant trend in driving urban growth. Its effectson urbanization from local neighborhood dy-namics to global clusters of cities have signif-icant implications on the local and global en-vironment. Precisely because agglomeration isboth a global and local phenomenon with noclear geographic boundaries, it accelerates andamplifies environmental changes, such as landconversion and habitat loss. The next sectionidentifies how the drivers of urbanization af-fect consumption and production activities inurban areas and consequently climate change,biodiversity, natural habitats, pollution, andhuman well-being.

4. BUNDLING URBANIZATIONAND SUSTAINABILITYGiven the enormous momentum underway thatdrives urbanization, the challenge confronting

the Century of the City is not whether to ur-banize but how to urbanize in ways that aremore sustainable and with less environmentalimpact. Here, we discuss recent research on ur-banization and global change in the context ofsustainability.

4.1. Urbanization as a Trigger forSustainability Solutions

Cities are agents of rapid change across a widerange of environmental, economic, and socialsystems. Agglomeration presents clear chal-lenges for urban governance, but it also opensup opportunities for sustainability solutions.How can we better assimilate our knowledge onthe new urban economic geography with ourunderstanding of the bidirectional effects be-tween urbanization and the global environmentto articulate a vision of, and action plan for,sustainability? This section integrates empiri-cal findings across different disciplines and sug-gests that increasing the number of urban ag-glomerations and the urban population withinthem can be part of the solution for global en-vironmental challenges.

New research shows several sustainabil-ity advantages of cities and urban areas withlarger populations (119). In addition to theeconomies of scale in terms of providing in-frastructure, education, health care, and san-itation services, there is evidence of increas-ing returns to innovation and wealth creationas urban areas become larger (120). Assumingthat a portion of that innovation will be di-rected toward responding to global environ-mental change, larger urban agglomerationshave higher chances of providing solutions forsustainability through new technological toolsand novel institutional arrangements. Using ascaling relationship between population andCO2 emissions for U.S. metropolitan areas,Lobo et al. (121) find that a 1% increase inpopulation (or economic output) is associatedwith only a 0.92% (or 0.79%, respectively)increase in CO2 emissions. A production-based analysis estimates that urban areas con-tribute to approximately 30% to 40% of total


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anthropogenic greenhouse emissions (122). Incontrast, a consumption-based analysis puts ur-ban contributions at 60% of total, with a fewwealthy cities contributing to a majority of theemissions.

Although agglomeration can present op-portunities for sustainability solutions, expan-sive urban land conversion has significant andfar-reaching environmental impacts. The scale,rate, and form of urban expansion affects lo-cal and regional temperature; precipitation pat-terns (123, 124); habitat and biodiversity (2,125); ecosystem function (53); the loss of agri-cultural land (126, 127); travel demand (128);atmospheric changes (129); and the demand forwater, energy, and agricultural resources (130),among many others. A recent study of globalpatterns of deforestation suggests that urbangrowth and the resulting changes in consumerdemand may drive agricultural exports and de-forestation (131). Thus far, the urbanizationand global change research community has fo-cused on cities as triggers of global environmen-tal change and has identified pathways throughwhich urban areas contribute to climate changewith a focus on carbon emissions (132). Re-search has only recently begun to disaggregatecities and the urbanization process and attributethe source of the problem to underlying factors,such as urban form, urban lifestyles, consump-tion preferences and opportunities, and energychoices (133).

At the same time, as shown in the previoussection, recent understanding from economicgeography suggests that urbanization canfacilitate the flow of ideas, and this, in turn, cantrigger innovation and economic growth. Al-though the connection between geography andgrowth was understood early on, the function-ing of cities was not central in the debates untilrecently (111). In the 1990s, the importance ofcities came to the forefront of economic growthprocesses through more elaborate concepts onthe effects of accumulation of technologies andideas (134) owing to the increased capacity ofhigher flows of knowledge and informationacross agents (135). Since then, empiricalresults heavily underscore the importance of

urban scale and density in increasing the pro-ductivity and creativity of firms and workers.This is an important point given the potentialeffects of a boost in technological, social, andinstitutional innovation processes for develop-ing sustainability solutions (136). Interactingdynamics in urban areas have the potential forbenefitting both urban populations and urbansustainability goals. Recent literature suggeststhat urban agglomerations—at least on thelevel of population—are part of the solution.The key is the arrangement of the ever largerpopulations of urban agglomeration intolocations, forms, and functions that promotesustainability. The next section showcasesexamples from the scientific literature inurban land-use planning of how this can beachieved.

4.2. Urban Land-Use Planning

Although planning institutions have shown lim-ited success in shaping urbanization, there arenew opportunities for them to direct urban-ization toward more sustainable forms, rates,and scales. Recent urban initiatives respond-ing to climate change have led to collabora-tions among local authorities, planning institu-tions, the scientific community, and local stake-holders from both the private and public sec-tors (137). There is an increased awareness ofthe role that cities can play to mitigate climatechange. Disciplinary studies have generated awealth of knowledge about urban areas (e.g.,economics, sociology, geography, climate stud-ies, hydrology, and engineering). However, thelack of integration between urban planning andsustainability concepts has been recognized fornearly two decades (138). Bridging the gap be-tween the science and practice of planning canhelp planning institutions better respond to thechallenges of urbanization in the twenty-firstcentury.

Recently, the planning community has pro-posed strategies to change traditional land-useplanning to incorporate elements of climatechange mitigation, adaptation, and sustain-ability. Tracing the history of environmental


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planning in the United States, Daniels (139)suggests that the current era, with its focus onsustainability and the global environment, willengender a new phase of planning that will gobeyond urban parks and managed growth toencompass a more systemic view of ecosystemwell-being. Global change scientists are alsorecognizing importance of local land-use plan-ning in achieving global environmental goals.In their review of atmospheric pollution innine megacities around the world, Molina &Molina (140) conclude that “Good urban plan-ning is needed to improve megacity air qualityby encouraging people to live closer to wherethey work, developing cost-effective and con-venient mass transit networks, creating eco-nomic activities outside of megacities to reducemigration incentives, and strategically locatingindustries.”

Urban areas contribute to climate change,and climate change is also a major threat forglobal urban areas. A recent study puts globalsea-level rise of 0.8 meters by 2100 “very likely,”with a range between 0.8 and 2 meters (141). Arise of 0.8 meters in sea level would be catas-trophic for many urban regions, not to men-tion the global economy. Urban responses toclimate change have grown rapidly during thepast decade in several parts of the world. Manyof those responses have focused on mitigat-ing the emission of greenhouse gases. The Al-liance for Climate Protection in the UnitedStates includes more than 800 cities that havepledged to reduce greenhouse gas emissions.The Canadian Federation of Municipalitieslists 150 members as part of its national cam-paign. Urban areas in Latin America, Europe,Asia, and Australia have initiated similar climateaction plans (142).

In contrast, fewer urban areas have be-gun to consider adaptation as part of theirresponses to climate change (e.g., London,New York, Chicago, Toronto, Seattle, Den-ver, Manchester, King County in Washing-ton State, Cartagena, Mexico City, Rotterdam,Durban, Cape Town) (142). Although climatechange presents significant challenges for cities,it is also an opportunity to raise political sup-

port and resources, achieve stakeholder partic-ipation in urban governance, and to update andimprove the knowledge and practice of urbandevelopment. Constructing multidimensionalperspectives of urban areas and climate changethrough the collaboration among scientists, lo-cal planners, decision makers, and stakeholderscan provide a solid basis to improve urban re-sponses to climate change and, at the same time,affect the scale, rate, and form of urbanization.

Furthermore, there are clear synergiesamong mitigation, adaptation, and urban devel-opment strategies. However, the focus on cli-mate change impacts obscures opportunities forreducing vulnerability in urban areas. Isolateddiscourses on adaptation and mitigation are un-likely to succeed and threaten to be insignificantif larger development issues are not taken intoaccount (143). To be effective, capacity build-ing for adaptation and development needs tosquarely address the structural inequalities thatcreate and sustain poverty, constrain access toresources, and threaten long-term sustainabil-ity (144). Despite the fact that social change isa central element of development, there is per-haps little attention to livelihoods in the effortsto connect vulnerability, mitigation, adapta-tion, and development. Rethinking frameworksfor development to better understand the com-plexity of global problems (socioeconomic andbiophysical) and their dynamic interaction intemporal and geographic scales with the locallevel is an area where further research is needed(142).

A point of clarification is in order in this dis-cussion. Mainstreaming adaptation and mitiga-tion strategies in urban policies can be achievedthrough formal mechanisms often found in ur-ban planning (building codes, land-use permits)and through economic incentives common inthe formal regulation of the built environ-ment in many urban areas of high-income andmiddle-income countries. However, it wouldbe unwise to neglect informal urban growthin many low-income and middle-income coun-tries. Those communities have some of themost pressing needs in terms of their vulner-ability to and ability to adapt to climate change.


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Creating adaptation and mitigation strategiesin these communities requires different meth-ods because urban growth takes place outsidethe formal framework of urban planning. Infor-mation on future scenarios of climate extremesand adaptation strategies is also a useful plan-ning tool for community-based organizationsand NGOs engaged in improving poor urbancommunities as well as for the local govern-ments that interact with them.

4.3. Can Rapid Urbanization Savethe Environment?

In light of the urbanization processes under-way, can the global environment afford not tourbanize? Put another way, what would be thedifferential impact of 3 to 5 billion new urbandwellers if they lived in different types of ur-ban settlements? To answer this question, weran a simple hypothetical scenario using UNestimates of the size of the new urban pop-ulation between 2010 and 2050. We calcu-lated greenhouse gas emissions from the growthof urban population hypothetically distributedacross three types of cities: high density, mod-erate density, and low density.

We used four total population scenarioswith variants in fertility derived from the UNWorld Population Prospects (145) and theprojected urbanization levels across regions in2050 to derive four possible urban futures. Thelow-, medium-, and high-fertility scenarios as-sume 1.35, 1.85, and 2.35 children per woman,respectively. The constant fertility scenarioassumes that, for each country, fertility remainsconstant at the level estimated for 2005–2010.That is, if the fertility rate for a country is2.1 children per woman during 2005–2010,it remains at 2.1 through 2050. By way ofcomparison, the world total fertility rate for2005–2010 is estimated at 2.56 children perwoman. The four population scenarios onlyassume differences in fertility rates. Otherscenarios exist that make assumptions aboutmortality and migration, but they are notincluded in our analysis. Under these fourfertility scenarios, the growth in global urban

population between 2010 and 2050 rangesbetween 1.9 billion and 4.7 billion people.

We used these estimates of projected ur-ban population growth to develop scenarios ofgreenhouse gas emissions. We used Washing-ton, DC, Toronto, Canada, and Seoul, SouthKorea, as our representative low-, moderate-,and high-density cities, with per capita green-house gas emissions circa 2000 of 19.7, 8.2, and3.8 tonnes, respectively. Using these reportedemissions per capita, we calculated global dis-tribution of total emissions assuming the newurban populations of each region lived in oneof the representative cities (122).

The results of this exercise are shown inFigure 5 (see color insert). The rows showdifferent population scenarios, and the barsshow the emissions associated with the growthin urban population living in different typesof urban settlements; low-, medium-, andhigh-density cities are shown in red, orange,and pink, respectively. Not surprisingly, if thegrowth in global urban populations resultsin low-density cities, this will result in thehighest greenhouse gas emissions. The high-fertility population growth scenario coupledwith low-density urban living leads to worldgreenhouse gas emissions of 786 billion tonnesin 2050. Caution should be given to the case ofEurope where the constant- and low-fertilityscenarios produce a reduction in greenhousegas emissions owing to a decline in total andurban population. Although the European caseshould be investigated further, especially be-cause these estimates do not capture migrationprocesses, the results clearly show that Asiais a major region of concern for the potentialeffects of future urban populations.

The critical point is that the scenarios showthat savings in emissions from different typesof urban development and associated lifestylesare tremendous, irrespective of the fertilityrate. Even with the low-fertility scenario, ifthe growth in urban population over the next40 years leads to low-density cities like Wash-ington, DC, this would result in an increaseof 380 billion tonnes of emissions in 2050.These calculations do not include cumulative


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emissions up to 2050, only emissions in theyear 2050. In contrast, if the growth in urbanpopulations is housed in high-density cities likeSeoul, the high-fertility scenario generates onlya total of 152 billion tonnes in 2050, less thanhalf of the total emissions under a low-fertility,low-density scenario. The constant fertilityscenario coupled with low urban densitiesproduces the highest emissions (937 tonnes),but this is the least likely population growthscenario.

Although this exercise is only illustrative, itis an important first step to asking the ques-tion of “How can we urbanize with less impacton the global environment?” This simple ex-ercise shows the magnitude of the gains—andcosts—associated with different types of urban-ization scenarios. The analysis does not factor inthe environmental and social costs of buildingand living densely. For example, how much landdo we save for nature, agricultural production,forests, and habitat when global populationslive in dense cities? Similarly, the analysis doesnot include all the environmental and socialcosts of building and living densely and the con-sumption effects associated with urbanization.The recent global study on deforestation sug-gests that, although urbanization may save landfor nature, urbanization can also result in anincrease in incomes, which then spurs demandfor agricultural and forests products, therebydriving deforestation elsewhere. There is muchwork in this area across disparate but comple-mentary fields. The challenge moving forwardis to develop multidimensional approaches tounderstanding the relationship between urban-ization and the environment that do not dependon a single solution.

5. CONCLUSIONS ANDFUTURE DIRECTIONS

Urbanization is occurring faster and at greatermagnitudes in geographic locations that are atlower stages of economic development and facerapid demographic changes. This, in turn, isaccelerating global environmental change. Ur-ban systems will continue to disproportionately

affect ecologically fragile areas and contributeto the loss of agricultural land compared toother systems. Urban growth in coastal andarid ecosystems will be particularly sensitive tothe effects of climate change. We project thatsprawling urban development will continue tobe the dominant growth pattern, but factorssuch as energy price shocks or economic down-turns could reverse or halt this trend. Urban-ization hot spots lack balance in their growth,such as adequate durable housing, access to im-proved water, key resources, and sanitation, andare also overcrowded, with high levels of un-employment and social exclusion. Institutionalsettings in such hot spots are weak, lack ac-countability, and face rampant corruption. Allthe above factors, operating in concert with cli-mate change impacts, create “stress bundles”that increase vulnerability to dangerous climatechange (146).

Agglomeration across scales continues to bea dominant global trend, presenting—on a firstlevel—benefits for urban sustainability. Thereare primarily two advantages from urban pop-ulation increase: (a) increasing returns from in-novation and productivity; and (b) economies ofscale in energy use, carbon emissions, and in-frastructure provision. Still, population is notthe only or most important factor shaping therelationship of urban areas with the environ-ment. This article highlights the importance ofother factors, such as urban form and function,institutions, and governance structure. The re-lationships between urbanization and the en-vironment, and thus opportunities for sustain-ability, are largely determined by the spatialityof urban areas. Higher densities of jobs and peo-ple can lead to more walking, less driving, lessenergy, and less carbon emissions. However,such outcomes require investments in publicinfrastructure that encourage transit develop-ment, as well as zoning that allows a mix of landuses (4). Infrastructure planning is also neededat a scale beyond that of an individual city.Rather, we need urban development strategiesthat take a “system of cities” perspective andthat formulate polices at a regional or nationalscale.


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In short, agglomeration cannot operatealone; it is just one piece of the puzzle of ur-ban sustainability. Integrated urban land-useplanning has potential for offering significantsolutions. Urban form and function interven-tions along with good urban governance canfurther assist in enhancing the process of sus-tainable development, but agglomeration playsa big role in putting communities on the rightpath. For the urban settlements that will behome to the 3 to 5 billion new urban dwellersover the coming decades, the challenge ahead isto leverage urban development efforts, includ-ing human and financial resources, to create so-lutions that simultaneously mitigate and adaptto climate change.

The challenge for humanity is how tochange the current scale, form, and rate ofurbanization to build opportunities for sus-tainability in both developed and developingcountries. We highlight in our discussion theneed of multidimensional and multiscale ap-proaches to better understand the complexityof urbanization in the twenty-first century.This is the best way to integrate current andfuture effort to respond (by mitigation and

adaptation) to climate change in urban areaswithin a broader framework of urban sustain-ability that helps build coherence and benefitsin the short- and long-term for societies.

We started this article by stating that we areentering a new era, the Astycene. Urban ar-eas have been a prominent feature of human-ity throughout most of history. Yet, we have ahard time recognizing how urban areas illus-trate the dramatic transformations in societiesduring the last century. The conflicts and im-balances among countries and within countriescreate severe obstacles to building efficient re-sponses to new challenges like climate change.The transition to an urban century illustratesthe need for a new way of thinking and un-derstanding the increasing complexities of oursocieties. Making sense of the new urban re-alities can contribute to a more comprehensiveunderstanding of our common future. Integrat-ing responses to climate change—by mitigationand adaptation—with strategies for urban de-velopment can help us transition to sustainabil-ity but will require multidimensional and multi-scale approaches to the study and managementof urban areas.

SUMMARY POINTS

1. Contemporary urbanization fundamentally differs from historic patterns in its scale, rate,geographic reach, form, and function, and it is characterized by its many interconnecteddimensions.

2. Urban areas are not just about the physical and built environment, but also about insti-tutions, governance, and social processes. We need to view urban processes as part of acomprehensive and complex system.

3. The physical structure and character of contemporary urbanization throughout the worldis increasingly similar to those of North American cities, but at larger scales and occurringwith greater rapidity. These trends are most evident in developing country cities and,if they continue over the next 40 years, will have significant implications for local andglobal sustainability.

4. In addition to demographic and economic forces, agglomeration, changes in governanceand institutions, and international capital are interacting to amplify their individual im-pacts on urbanization processes and are accelerating changes in the physical structureand character of urban areas.

5. Contemporary urbanization has the potential to help the transition to sustainabilitysolutions because of gains from scale in innovation, productivity, and efficiency.


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6. The way the scale, form, and rate of urbanization takes place makes a significant impacton sustainability. However, we need to develop a multidimensional and multidisciplinaryperspective.

7. Historically, urbanization has been viewed as an environmental ill, but rapid urbaniza-tion can actually accelerate a transition to sustainability owing to forces of agglomeration,increased innovation, and increased wealth. However, urban growth needs good gover-nance structures in order to achieve this.

FUTURE ISSUES

1. How can perspectives on and agendas for sustainability explicitly incorporate futureurbanization?

2. What are the most significant opportunities to develop triple-win solutions and strategiesfor climate change mitigation and adaptation and urban development?

3. How will the confluence of contemporary urbanization and global environmental changeexacerbate or accelerate issues of equity?

4. We have a very limited understanding of the dynamic interactions in urban areas. Whatare the complex interactions between institutions, governance, energy choices, and builtspace? What are the social outcomes of the built environment?

5. What forms of urban growth have less environmental impact? And what are the gover-nance and institutional structures necessary to achieve them?

DISCLOSURE STATEMENT

The authors are not aware of any affiliations, memberships, funding, or financial holdings thatmight be perceived as affecting the objectivity of this review.

ACKNOWLEDGMENTS

The authors would like to thank Qingling Zhang and Tianming Chen for help with the figures.

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EG35-FM ARI 18 September 2010 7:49

Annual Review ofEnvironmentand Resources

Volume 35, 2010 Contents

Preface � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �v

Who Should Read This Series? � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �vii

I. Earth’s Life Support Systems

Human Involvement in Food WebsDonald R. Strong and Kenneth T. Frank � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 1

Invasive Species, Environmental Change and Management, and HealthPetr Pysek and David M. Richardson � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �25

Pharmaceuticals in the EnvironmentKlaus Kummerer � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �57

II. Human Use of Environment and Resources

Competing Dimensions of Energy Security: An InternationalPerspectiveBenjamin K. Sovacool and Marilyn A. Brown � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � �77

Global Water Pollution and Human HealthRene P. Schwarzenbach, Thomas Egli, Thomas B. Hofstetter, Urs von Gunten,

and Bernhard Wehrli � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 109

Biological Diversity in Agriculture and Global ChangeKarl S. Zimmerer � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 137

The New Geography of Contemporary Urbanization and theEnvironmentKaren C. Seto, Roberto Sanchez-Rodrıguez, and Michail Fragkias � � � � � � � � � � � � � � � � � � � � � 167

Green Consumption: Behavior and NormsKen Peattie � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 195

viii

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EG35-FM ARI 18 September 2010 7:49

III. Management, Guidance, and Governance of Resources and Environment

Cities and the Governing of Climate ChangeHarriet Bulkeley � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 229

The Rescaling of Global Environmental PoliticsLiliana B. Andonova and Ronald B. Mitchell � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 255

Climate RiskNathan E. Hultman, David M. Hassenzahl, and Steve Rayner � � � � � � � � � � � � � � � � � � � � � � � � � 283

Evaluating Energy Efficiency Policies with Energy-Economy ModelsLuis Mundaca, Lena Neij, Ernst Worrell, and Michael McNeil � � � � � � � � � � � � � � � � � � � � � � � � � 305

The State of the Field of Environmental HistoryJ.R. McNeill � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 345

Indexes

Cumulative Index of Contributing Authors, Volumes 26–35 � � � � � � � � � � � � � � � � � � � � � � � � � � � 375

Cumulative Index of Chapter Titles, Volumes 26–35 � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � 379

Errata

An online log of corrections to Annual Review of Environment and Resources articles maybe found at http://environ.annualreviews.org

Contents ix

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AnnuAl Reviewsit’s about time. Your time. it’s time well spent.

AnnuAl Reviews | Connect with Our expertsTel: 800.523.8635 (us/can) | Tel: 650.493.4400 | Fax: 650.424.0910 | Email: [email protected]

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Annual Review of Statistics and Its ApplicationVolume 1 • Online January 2014 • http://statistics.annualreviews.org

Editor: Stephen E. Fienberg, Carnegie Mellon UniversityAssociate Editors: Nancy Reid, University of Toronto

Stephen M. Stigler, University of ChicagoThe Annual Review of Statistics and Its Application aims to inform statisticians and quantitative methodologists, as well as all scientists and users of statistics about major methodological advances and the computational tools that allow for their implementation. It will include developments in the field of statistics, including theoretical statistical underpinnings of new methodology, as well as developments in specific application domains such as biostatistics and bioinformatics, economics, machine learning, psychology, sociology, and aspects of the physical sciences.

Complimentary online access to the first volume will be available until January 2015. table of contents:•What Is Statistics? Stephen E. Fienberg•A Systematic Statistical Approach to Evaluating Evidence

from Observational Studies, David Madigan, Paul E. Stang, Jesse A. Berlin, Martijn Schuemie, J. Marc Overhage, Marc A. Suchard, Bill Dumouchel, Abraham G. Hartzema, Patrick B. Ryan

•The Role of Statistics in the Discovery of a Higgs Boson, David A. van Dyk

•Brain Imaging Analysis, F. DuBois Bowman•Statistics and Climate, Peter Guttorp•Climate Simulators and Climate Projections,

Jonathan Rougier, Michael Goldstein•Probabilistic Forecasting, Tilmann Gneiting,

Matthias Katzfuss•Bayesian Computational Tools, Christian P. Robert•Bayesian Computation Via Markov Chain Monte Carlo,

Radu V. Craiu, Jeffrey S. Rosenthal•Build, Compute, Critique, Repeat: Data Analysis with Latent

Variable Models, David M. Blei•Structured Regularizers for High-Dimensional Problems:

Statistical and Computational Issues, Martin J. Wainwright

•High-Dimensional Statistics with a View Toward Applications in Biology, Peter Bühlmann, Markus Kalisch, Lukas Meier

•Next-Generation Statistical Genetics: Modeling, Penalization, and Optimization in High-Dimensional Data, Kenneth Lange, Jeanette C. Papp, Janet S. Sinsheimer, Eric M. Sobel

•Breaking Bad: Two Decades of Life-Course Data Analysis in Criminology, Developmental Psychology, and Beyond, Elena A. Erosheva, Ross L. Matsueda, Donatello Telesca

•Event History Analysis, Niels Keiding•StatisticalEvaluationofForensicDNAProfileEvidence,

Christopher D. Steele, David J. Balding•Using League Table Rankings in Public Policy Formation:

Statistical Issues, Harvey Goldstein•Statistical Ecology, Ruth King•Estimating the Number of Species in Microbial Diversity

Studies, John Bunge, Amy Willis, Fiona Walsh•Dynamic Treatment Regimes, Bibhas Chakraborty,

Susan A. Murphy•Statistics and Related Topics in Single-Molecule Biophysics,

Hong Qian, S.C. Kou•Statistics and Quantitative Risk Management for Banking

and Insurance, Paul Embrechts, Marius Hofert

Access this and all other Annual Reviews journals via your institution at www.annualreviews.org.

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the new geography of contemporary urbanization and the environment

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