Global suburbia and the transition century: Physical suburbs in the long term

Over the current century, when the world’s population will grow by some billions, much of the increase in the human population will be housed in suburbs. However, sometime after the middle of this century the world’s total population is also likely to level off, increasing in some areas while declining in others, causing new challenges. In this transition century, suburbs are a key technology and setting for managing a number of public concerns and problems: population change, aging, environmental issues, and tensions between continued poverty and expectations of affluence. Suburbs are very diverse internationally but share some common problems and opportunities related to their relative newness and outer location. Although planned solutions to suburban growth are important, a great deal of work in the coming century will be retrofitting opportunistic suburban development. A global view of suburban growth is important because physical planning and urban design have long shared ideas internationally, and because of global economic, environmental and cultural linkages.


Introduction: The Importance of Suburbs
Beyond the core of every large urban area is a band of development called suburbs. What proportion of the urban or metropolitan area is seen as suburban depends on how one defines suburbs and such definitions are numerous. What is certain, however, is that over the current century, when the world's population will grow by some billions, a substantial part of the increase in the human population will be housed in suburbs. However, the story is complicated as toward the middle or end of this century the world's total population is also likely to level off, increasing in some areas while declining in others, causing new challenges for a planet that has become accustomed to growth. This decline is already happening in some metropolitan areas.
In this transition century, suburbs are a key setting and technology for managing a number of public concerns and problems about urban development. However, they are also where many people seek to live out their dreams and aspirations at the individual and household level. What are the opportunities and challenges posed by this coming wave of suburbanization, suburban shrinkage and suburban redevelopment? In a century it is possible to alter what is the commonsense in terms of urban development but by then a very large amount of suburban development will be already builtis what is being put into place now adaptable to the future century's needs?
The article first outlines how suburbs can be defined in a way that makes sense internationally focusing on location and newness. It then examines potential changes in the patterns of urbanization globally, and the role of suburbs in facing a slowing of growth, population aging, environmental problems and issues of inequality. Planners have differing ideas about how to tackle these challenges. Although there is something of a consensus vision in many urban design and planning circles of a sustainable, multi-centered, participatory metropolitan area that concentrates developments in accessible districts and respects the landscape, there is a lot of current and likely future suburban development that will not take that form (Forsyth and Crewe, 2009;Loukaitou-Sideris, 2012). The article reviews the range of common physical planning and urban design approaches to improving suburban areas at a smaller scale, the district, showing their diversity. It then proposes long-range global scenarios as tool that could be more widely used to imagine plausible futures and assess the quality of planning and design solutions at the building, district and regional scales. Future suburbs need to be adaptable for growth, decline or both over time. Urban designers need to understand and engage with these issues to be part of a continuing global conversation.
To make this argument I have to confront three potential objections. First, it can seem as if all (suburban) development is local so that a global view of suburbs is overdrawn. Suburbs are diverse enough within one country, let alone internationally. However, it is also obvious that local activities are connected not only nationally but in the global economy, the global environment and in global culture. Patterns of development in one place have effects elsewhere. Planning, design and development ideas are shared internationally among professionals, activists and the wider public. Certainly some aspects of suburban development are very specific to a time and placefor example the substantial power of US suburban governments to shape educational opportunities. But other topics are usefully examined in a global context, for example how to redevelop existing suburbs to be more sustainable or create new outer areas in a polycentric city. The problems and opportunities of outer location and relative newnesskey features of suburbshave certain similarities in many places (Harris, 2010).
The second problem is that to make this kind of argument I have to draw on (at least) three substantial bodies of literature that are often independent. First is the work on suburbanization and suburban character. This typically focuses on more affluent countries and includes scholarship from urban planning, history, sociology, geography, economics and political science. 1 Second is the literature on urban development in lower-and middle-income countries. This work often talks about peri-urban development or decentralization rather than suburbanization; discussions of suburbanization are often restricted to more affluent 'Western' or 'US-style' suburbs which are seen as an expression of elite business practices and cultural influences. Finally, the literature on global futures that seldom focuses on specifically urban futures. The differences in perspective are substantial. At least part of many interdisciplinary projects involves translating what is brutally obvious in one field into terms understandable in another and this is certainly the case here. However, to solve important problems, scholarship (and practice) need to engage with these multiple dimensions. This will require some rapprochement from all sides although there are many encouraging signs (for example, Beard et al, 2008;Wu and Phelps, 2008;Gans, 2009;Song and Ding, 2009;Watson, 2009;Clapson and Hutchinson, 2010;Harris, 2010;Audirac et al, 2012;Chattopadhyay, 2012).
The third issue is the ambivalence of many urban scholars and urban designers about suburbs. For example, the substantial boom in housing production in the 1950s -when units constructed in the US more than doubled over their levels in the half century before (Hise, 1997) in turn sparked a more international wave of criticism of suburban culture, seen as conformist, isolating and visually ugly. Titles like Lonely Crowd (1950), Organization Man (1956), Australian Ugliness (1960), and Feminine Mystique (1963) exemplified the general tone of such criticisms (Riesman, 1950;Whyte, 1956;Boyd, 1960;Friedan, 1963). A little later more practical concerns emerged about the problems of Traffic in Towns (1963) combined with larger discussions about Limits to Growth (1972) and the environmental and economic Costs of Sprawl (1974) (Ministry of Transport, Great Britain, 1963;Meadows et al, 1972;Real Estate Research Corporation, 1974). By the end of the century debates encompassed all these dimensions and had moved to an even more global stage with particular concerns about congestion, social connectedness (some saying there was too much in suburbs and others too little), social exclusion, conspicuous consumption, health and placelessness (see reviews in Eichler and Kaplan, 1967, pp. 4-10;Popenoe, 1977, pp. 2-8;Gans, 1963;Forsyth, 2005;Harris, 2010). Of course some have defended suburbs either as a type or in terms of the more glaringly one-sided attacks (Breugemann, 2006;Barker, 2009).
Certainly these criticisms and defenses have been usefuloften highlighting real concerns about suburban development or important blind spots and biases in debates. However, solving the problems of first housing substantial increases in urban residents and then managing suburbs with flat or declining, and aging and impoverished, populations requires more than critique. It also requires a view that looks beyond just the examples of the United States and Western Europe, or even of economically and culturally important global cities worldwide.

What Suburbs Are
Many people, of course, have fairly fixed views of what suburbs are, imagining rows of cookie cutter houses filled with nuclear families owning 2.1 cars. However, such locations are only a small proportion of suburbshow small a proportion depends on the specific definition of suburbs one is using. For many people suburbs are defined by their built environment or activities, for example as places with many detached houses, as mainly residential in land use, or that are automobile-oriented (Turcotte, 2008). Others emphasize a culture, social order or way of life (Harris and Larkham, 1999, p. 8;Johnson, 2006). In the United States, suburbs are frequently defined as metropolitan municipalities outside the core city (Teaford, 2008). Others perceive suburbs as essentially white and affluent, making some think they are less deserving of attentioneven though a vibrant literature on suburban history and sociology has pointed out the many exceptions to this characterization (Nicolaides and Wiese, 2006). Some environments from squatter settlements in poorer countries to elite architect-designed houses in richer onesare not considered by some writers to be suburban, even if they are clearly such in terms of location (Davis, 2006;Neuwirth, 2006).
In the international urban studies literature, locational or temporal definitions of suburbs are often prominentparticularly definitions related to outer location, relative newness and lower density (Forsyth 2012;Harris, 2010). The first two characteristics in particular can be used to identify suburbs globally as they take into account the variety of suburban types from industrial suburbs to ethnoburbs (though they need to be stretched a bit to take account of older villages and towns swallowed up in suburban development). These dimensions lead to a number of similar characteristics of suburbs, for example problems with regional accessibility and the need to establish new social connections and physical infrastructure (either over time of at substantial initial cost) (Harris, 2010).
This article takes this broader, more international view, defining suburbs in terms of their location and newness. In terms of location suburbs are on the outer parts of metropolitan areas, although that can be a very wide band in larger cities. They are new in the sense of most of their fabric having been built since widespread use of automobiles, motorcycles, motorized buses and trucks. This provides a focus on what would often be called middle and outer rings of suburbs, and the suburban fringe. These are the frontiers of developmentat the urban edge but also existing suburbs where the built fabric is aging or under stress. From cheaply built subdivisions, to large and hard-to-maintain custom houses, under-serviced squatter settlements, aging high-rise social housing, and prefabricated warehouse space designed for use over a short time period, there are substantial mismatches between current or future needs and existing environments. However, whether one defines suburbs broadly or narrowly (for example, as automobile-based outer residential development) there will be many suburbs built new, and still more redeveloped, in the current century. 2

The Transition Century
Facing uneven growth These challenges that will be faced in suburbs in this century are in many ways unprecedented. The past century brought a massive increase in population from about 1.6 billion in 1900 to over 6 billion in 2000 (see Figure 1). In 1900 the average human lived just 31 years (50 in richer countries such as the United States) (Cohen, 2006;Prentice, 2006). By 2000 average life expectancy had more than doubled (to 62 years for males and 67 for females) reaching more than 20 years beyond that in highly urbanized places such as Japan, Singapore and Australia (UN, 2004;CIA, 2011). 3 Significant aspects of life that seem normal todaythe presence of grandparents or long marriageswere not part of a world where most people died young. During the twentieth century an increasing proportion of the world's growing population moved to all parts of urban areas, including suburbs, rising from around 15 per cent of the world's population in 1900 to about 50 per cent today (Satterthwaite, 2007a, p. v). By 2010 there were perhaps 50 000 'urban' settlements worldwide, where urban is defined as relatively compact settlements of at least a few thousand people with specific definitions varying by country (Satterthwaite, 2007a, b, pp. 4-5). In 1900 there were only 16 or 17 metropolitan areas of a million people or more (Chandler, 1987;Harvey, 1996, p. 403;Satterthwaite, 2007a, pp. 6-7). Even using a restrictive UN estimate, by 2010 450 metropolitan areas had populations of a million or more (Satterthwaite, 2007a, p. 10;Satterthwaite, 2007b, p. 12). 4 However, importantly for my argument there are literally thousands of settlements over 100 000 in population, making up approximately two thirds of the current world urban population (UN, 2010a, p. 5). These metros are quite large enough to have suburbs.
Much attention in urban scholarship focuses not on the many ordinary cities that house most of this urban population however, but on two other types, megacities and global cities (Robinson, 2002). Megacities, those with 10 million or more people, made up only 5 per cent of the world's population in 2000 (10 per cent of the urban population) and the proportion is not likely to increase much in coming decades (Satterthwaite, 2007b;UN, 2010a, p. 5). 5 Something similar can be said about the important economic and cultural centers or 'global cities', locations such as Mumbai, New York, Tokyo, Sydney, Singapore and Beijing (Global and World Cities, 2008; AT Kearney, 2010). Such places will certainly grow and have suburbs, have benefited greatly from globalization of the economy and culture (even if internally unequal), capture much academic attention, and have pleasant tourist bubbles. However, they will house a relatively small proportion of the world's population particularly relative to the large amount of attention they garner in the press and in scholarly circles (Robinson, 2002).
It is notoriously difficult to project future populations and the past is littered with examples of over and under estimates. 6 The UN projects that world population will increase by a middle value of 2.3 billion between 2009 and 2050, but that urban areas will gain 2.9 billion with the balance due to rural to urban migration. At that time the world would be almost 70 per cent urban (Montgomery et al, 2003, p. 4; UN, 2010a, p. 1; Figure 2). Assuming cities and towns maintain their positions as sources of job growth, most growth in the early part of the century will be in urban areas in low and middle income countries (see Figure 3). Asia already has half the world's urban population and Africa has more urban residents than North America. Looking a bit further in the future about one-third of urban population growth from 2009 to 2050 will be in India and China (36 per cent to 2025, 31 per cent  from 2025 to 2050) (Satterthwaite, 2007a, p. 3; UN, 2010a, p. 12; Table 1). 7 The exact cities that grow will depend on many circumstancesfrom patterns of global investment to the shocks of natural hazards. 8 But the basic point from lists such as those in Table 1 is that many of these fast growing cities are not household names. This is more so the case with the many smaller cities not in this list because they were not yet at 750 000 population in 2009 when the data were compiled. And such metros will have suburbsboth broadly and narrowly definedand including both economic activity (jobs) and residences (Hall, 1999). Figure 4 provides evocative examples of fast growing, cities that are not household names globally.
Although projections assume that populations will increase in the near term, many 'middle' and 'low' projections also chart a challenging new course where sometime between the middle and end of the century a new trend will emergeglobal population growth will slow and perhaps even stop (Montgomery et al, 2003;UN, 2004, p. 2;Satterthwaite, 2007a, b, p. 28). Population shrinkage is already being faced in some metropolitan areas, due to uneven patterns of investment, but may well become pervasive (Martinez-Fernandez et al, 2012). 9 Certainly even with a flat population people could move to locations with more opportunities and household size could drop, necessitating more building, but the last century's pattern of relentless expansion will slow. The world has been growing for the contemporary planning profession's entire historyand certainly for the briefer history of the contemporary form of urban designthis transition is a major change (Krieger, 2006). Suburbs, which have often grown at the expense of core cities, will themselves shrink.

Challenges for suburbs
Combined with the other global problems of environmental damage and inequality, these demographic changes present four major sets of challenges that will have key sites in suburbs.

Uneven growth
Whether short-term (30-year) urban growth is enormous or just very large, metropolitan areas will face difficulties. Many will grow, a lot, and then slow; a few will decline in population fairly constantly; some will have uneven expansion. In a world that has been rapidly growing for over 200 years this is a fundamental change. Many of the places that face these challenges will be smaller metropolitan areas or suburban municipalities. Even in richer countries they may not have fully developed urban governance with implications for providing infrastructurefrom clean water to transportationand coordinating regional growth (Satterthwaite, 2007b, p. 57). Urban design interventions are likely to be piecemeal and fragmented.
Practically, it is complicated to plan for both growth and continuity or decrease but the time horizon is long. Some decline will be dramaticlike the loss of population in New Orleans after Hurricane Katrinabut many other examples will involve slow emptying of populations as in parts of the former Soviet Union or the US rustbelt. For a while, the incredible growth in places such as China will be hard to ignore. Growth is captivating. It needs to be put in perspective, however.

Longer lives
The twentieth century brought dramatic changes in women's roles; in the twenty-first century there are likely to be equally major changes around aging (Castells, 1997). In 2000, 10 per cent of the world's population was over 60. The medium UN projection is for 30 per cent in 2100 with an average Source: Developed using UN (2010b).
Global suburbia and the transition century life expectancy in the 80s. The ratio of children and elderly to working aged people (15-59) will increase from 0.67 to 0.88 over the century (UN, 2004, annex). In a world where social, and urban, systems have been set up under the assumption that there will be many working aged people for every retired person this is a change. 10 By the end of this century basically all locations in the worldeven Africa, a demographically young continent -will likely have a population dominated by those over 40 and with substantial numbers in their 70s, 80s and above. Around the world suburbs have offered younger people less expensive housing; in a world where most people are older they will have a different role. 11 Even with healthier aging this is a large changein family life, social support, retirement incomes, and in how people interact with places including suburbs. Here outer location is likely the most crucial issue; some suburbs will be well placed for older people who can no longer drive or who need other support. Houses might be large enough for intergenerational or group housing; many suburbs have vibrant and convenient town centers. They can be redeveloped at a human scale. But many suburbs will need extensive retrofitting and some may be just too expensive to service with implications for the possibilities of aging in place.

Damaged natural environment
Environmental damage has been a key concern of urban planning for some decades. Environmental planning is a major specialty in most professional programs. As such there has been substantially more thought paid to it than the population transitions above (Chapin, 2012).
However, this area has some specific interactions with suburbsnew suburbs bring people closer to rural lands and natural areas, providing a naturalistic urban design character, but they also use up such areas. Development in suburbs will have implications for energy use, levels of local pollutants and opportunities for sustainable employment (Newman and Kenworthy, 2000;Berke, 2008). Probably the strongest and most internationally valid critique of suburbs is that they overuse resourcesland, energy, water.
City: Ghaziabad India (#2*) is a satellite city of Delhi (20km away) and soon to be linked through the new metro system. With a population of about 1 million it is a manufacturing center that was named the "hottest city" in India in 2006 by Newsweek (Raaj 2006;National Informatics Centre 2011). Illustrations show advertisements for new high rise housing, a garbage dump in the middle of the built-up area, and a new shopping mall.
City: Heze China (#68*). The population of the actual city is not clear but it is part of a larger City of Heze region of over 12,000 square kilometers with a population of over 9 million (many Chinese Cities have such generous boundaries [Cohen 2006, 66]). Located mid-way between Shanghai and Beijing it has a number of industries including agriculture; manufacturing; oil, coal, and gas mining (Shangdongbusiness.gov.cn n.d.). Illustrations show local farmers selling vegetables in a vacant lot, new development on the urban edge, and vendors outside automobile show rooms on the urban edge. Solutions, however, cannot realistically just involve re-urbanizing the core cities but will also involve work in suburbs; and ideas for ecologically sustainable suburbs, while provocative and useful, have not yet grappled enough with other trends such as aging (Pillemer et al, 2011).

Continuing poverty and heightened expectations
Since 1980, according to some accounts, there have been reductions in the number of very poor worldwide, and global income inequality has declined slightly. However, wages are becoming more unequal globally (wages are only part of household income) and there is increased within-country inequality in several major nations including the United States, China and India (Dollar, 2005). Many hundreds of millions of urban dwellers still lack clean water and connections to sewer systems; others live in crowded conditions and shacks or on land subject to flooding and landslides.
Globally many of the poor live in suburbs due to the lower cost of land. The international suburban and housing literatures has a long tradition of work on suburban disadvantage and isolation (for example, Maher, 1994;Orfield, 2002;Moran, 2011;Audirac et al, 2012;Hebert et al, 2012).
However, much of the recent literature specifically on suburbs in a global perspective has focused on elite, gated and what are termed 'USstyle' suburbs (Fishman, 2003;Leichenko and Solecki, 2005;Xue and Zhou, 2007;Lara, 2011). These represent substantial affluence, are typically inhabited by people aware of global trends, and are certainly important. Business growth relies on selling more things and experiences to more people (Castells, 1997;Marcuse and van Kempen, 2000;Knox, 2005). Suburbs are important locations because they are areas where extensive development occurs and dwellings are typically larger than in core cities. Even in more modestly produced areas suburban development can absorb a lot of products.
However, while such elite suburbs are important both poverty and affluence will play a role in suburbs. I call this issue one of inequality but it is much more than that in realityit is part of an uneven economic landscape (Marcuse, 2006). That both poverty and affluence happen in suburbs muddies international discussionsparticular debates tend to focus on one or the other. But both are strongly present in suburbs and provide important, though different, challenges for urban designers and planners.

Evaluating the Physical Planning Toolkit: Built Environment Framing implementable answers
What can urban designers and planners do to meet the challenge of this suburban future? What are the special implications for suburbs beyond those generally brought about by urbanization as a whole? In the physical planning and urban design toolkits, what strategies are available? Can suburbs, as major growth components of urban areas, be developed and redeveloped to provide solutions for these urban challenges that will work in enough places to make a difference? This is not a situation with very easy answers. As has been demonstrated in numerous fields, from history to game theory, important human aims -such as global sustainability and personal aspirations for a good life -are not intrinsically in harmony. This creates the potential for a significant clash between, in this case, what people need to flourish in the way they have come to understand that term, and what the planet needs to survive in a way that is relatively intact (Ignatieff, 1984). Around the world there are obvious examples of this problemeroding landscapes, lost habitat, polluted water and social dislocation. Some places manage to coordinate growth in a way that provides opportunities and a high quality of life for most residents, but many do not (Hall, 1999;Watson, 2009). This inquiry is both helped and made more complex by the substantial variety among existing suburbs from elite suburbs in global cities to self-build homes and mass produced apartments. People with low incomes can buy inexpensiveif unserviced and inaccessiblesuburban land and build a home gradually. Affluent people can buy large amounts of land for uniquely designed homes close to natural features. There is a long tradition of transitoriented suburbs served by trolleys, railways and special buses; densities in these areas can be very high. Some suburbs are very diverse physically and sociallywith ethnic clusters, diverse incomes or lifestyle enclaves. Some suburban areas started up as independent towns but came to function as suburbs as they were surrounded by development. There are many variationsdifferent in look, amount of development, regulations, income level, social arrangements, and so on (Forsyth, 2012).

Solutions also differ in several other important dimensions:
• Scales of activity: the region or metropolis, the district, and the building. These scales involve different actorsfrom residents to regional governmentsand different strategies from green building to regional plans. Innovative ideas that may be achievable at a small scale and attractive to a select group of people may not sell to tens or hundreds of thousands of people or, if regulations, may not have the potential to be applied broadly beyond one neighborhood or city. • Types of development: these include completely new land conversion, replacement of existing buildings, and renovations or adaptations. Using data from 2000, Nelson (2004) projected that by 2030 nearly half of the buildings in the United States would have been built in the previous 30 years and almost 40 per cent of this would be replacement of existing structures; commercial and industrial buildings in particular tend to have short lives (see Figure 5). Although likely delayed by the recession, this demonstrates the huge scale of potential development in coming decades even just looking at replacement; in growing areas the extent of development is even larger. • Adaptability to change over time: As changes occur, built places need to be flexible enough to allow other uses, amenable to being efficiently rebuilt, or perhaps designed to be gracefully abandoned. Basically all of the well-loved urban places in the world have gone through multiple stages of rebuilding or have inbuilt flexibility (think of the ways urban cores have been redeveloped numerous times, for different users and purposes, with the same street patterns and even the same basic building types). Regulation may stifle positive change; a lack of it can provide so little coordination that there is a lot of waste.

Current options
Worldwide there will of course continue to be a great deal of opportunistic development that is minimally regulated or reflects political and economic connections over the public interest (Watson, 2009). It is not just a matter of McMansions sprawling across farmland in the United States but of high-rise apartments popping up in unserviced paddy-fields elsewhere. There is a lot that is positive about self-built housing in suburbs but also long-term challenges in providing services and real problems if such housing is built on hazardous land. In areas where suburbia has lower densities some solutions may need to reduce densities even more and take some forms of development back to nature. In places where suburbs have very high densities the problem to solve may be providing adequate infrastructure and retrofitting universal design as people age (not as simple as it sounds in many locations). There will be much of this kind of opportunistic development in coming decades so finding solutions to retrofitting it will be important. When looking at more planned responses to suburbanization, however, urban planners and designers are also divided on how to improve upon this current situation. In this section I look at the scale of the districtbetween the building and the region. These last twothe building and the regionare very important. The district scale, however, is a key part of public and professional debates (for example, it is a scale that design professionals understand and journalists write about). It also arguably has less of a consensus compared with arguments for green and efficient buildings on one hand and coordinated regional plans (with multimodal transportation corridors in a multi-centered urban form respecting important landscape features) on the other (Forsyth and Crewe, 2009). Of course divided opinions are often for good reasons, because different places have different challenges. But they may also represent the mismatch between traditional scholarship and practice in this area, and the fast pace and global reach of this change. In Table 2, I list a number of the most common approaches to improving areas at this scale, and assess their problems and benefits. In doing this I look back to the four challenges for suburbs (uneven growth, aging, environmental damage, inequality) and the implementation issues of scale, development type and adaptability (Table 2; see Figure 6, for examples of current suburbs).
Some planned approaches are more incremental though conforming to some set of overall regulations, or regional plans. Approaches that intensify development in particular areas, perhaps those well serviced by public transport, can help make development more efficient. Intensification strategies lead to less need for new suburbs. Around the world, even in richer countries, many  Grant and Mittelsteadt (2004), Hall (2002), Krieger (2006), Lang (2005), Osborne and Whittick (1977), Newman and Kenworthy (2000), Newman et al (2009), UN Habitat (2010. a There is also a great deal of work that develops one building at a time to reflect individual preferences. b See section on 'Challenges for Suburbs' and 'Framing Implementable Answers' for explanation. Global suburbia and the transition century suburbs have been developed with rather modest initial services and these were upgraded later. For example, both in the United States and Australia, many suburbs of the 1940s and 1950s were developed using septic tanks that were then replaced in a more coordinated manner (Hayden, 2003). Although more expensive to retrofit, and not taking full advantage of the potential for infrastructure to shape suburban form, it has a long history. Better approaches will be needed internationally for such upgrading.
Urban designers thinking about solutions to urban problems often think of more focused solutions such as those in the second half of the table. These try to solve key perceived problems of suburbs such as placelessness, homogeneity, a lack of appropriate services or a lack of jobs (for example, Vall-casas et al, 2011). They create imageable places and can be highly influential, though to make a major positive difference in suburbs they typically need to be part of a larger regional system. 12 They are not all equivalent, however. Those seeking or promoting access to nature, a sense of place or economic growth alone can command many resources and have a big impact without engaging much with the challenges of aging, environmental damage (particularly efficient transportation) or inequality.
There is also of course a range of community development, social life and governance-focused approaches not listed in Table 2 from suburban poverty alleviation and participatory budgeting to small business training and land regularization. Given the large social changes envisaged, these non-physical methods will be important and perhaps easier to implement than changes to the built environment. However, assessing which ones will be effective in improving suburbs is still a problem (Watson, 2009).

Testing scenarios
Rather than try to evaluate approaches such as those in Table 2 in terms of abstract principles, one can also think about how they might engage alternative possible futures. Of course, there have been many inaccurate predictions about the future. A town centre in outer suburban Sydney, Australia. One approach to managing this situation is to create plausible scenarios about a range of possible futures and design strategies that can cope with both the alternative general futures and the specific suburban challenges: uneven growth, longer lives, environmental damage and the tensions around inequality. Better suburban solutions would be able to weather the worst scenarios and help fulfill the best. What might a very long-term scenario look like? A number of bodies build such scenarios that combine projections and forecasts with stories about possible futures (Myers and Kitsuse, 2000;Quay, 2010). I use just two existing examples to show some of the range. Royal Dutch Shell is famous for creating scenarios so it can plan its very long-term land and infrastructure investments (Wack, 1985). It does these fairly frequently and in 2008 developed its 'scramble' and 'blueprint' scenarios for 2050.
• Scramble: Countries focus on their own energy security with bilateral deals; coal and biofuels increase; carbon production increases; and climate and political instability result. • Blueprint: This scenario involves more regulation, initially led by specific cities and regions, and carbon trading matures early. This is a more stable scenario with more affordable energy prices (Shell, 2008).
These are not necessarily desirable futures but rather possible ones that a company needs to be ready for. By 2050 blueprint uses only 15 per cent less energy than scramble, however (Shell, 2008, p. 46). The Global Scenario Group run by NGOs in Sweden and the United States has worked on a wider range of scenarios ending in 2100.
• 'Market forces' and 'policy reform' have much in common with scramble and blueprint in that the world evolves 'without major surprise[s]' (Raskin et al, 2002, p. 14). • Two more focus on deteriorating situations -an authoritarian and gated 'fortress world' and a more dramatic 'breakdown' where multiple crises lead to the collapse of institutions, economies and cities. • A final two, that they call 'great transitions', are more focused on sustainability: 'eco-communalism' is a vision of local democracy and bioregionalism; 'new sustainability' is more positive about urban life and global links and will be more recognizable to planners (Raskin et al, 2002; see similar range in Newman et al, 2009).
Obviously, these scenarios are developed at least in part to promote the last two rather than to have people prepare for literally all of them. These are certainly not the only possible scenarios but they give a sense of the range of current scenario thinking. Could urban designers and planners do better than this in imagining multidimensional urban (including suburban) futures at a global scale? Sure. Have they? Not yet.
Generic suburban growth would be somewhat different under each of these possible futures. For example, it may be more unequal under 'fortress world' and to some extent 'market forces'. In this situation planners would be challenged to promote equality in a context hostile to it. Suburban growth would be more regulated under 'policy reform' and 'new sustainability'. Under 'breakdown' and 'eco-communalism' there is a great deal of decentralization (though it is more orderly in the latter scenario). Currently such scenariosoften focused on the big environmental and political trends of the time -deal rather less with issues such as aging populations or the details of development within cities. However, one could imagine that the approaches under the ideas of infrastructure improvement, efficiency and diversity in Table 2 would fit well with 'new sustainability' while some of those focused on ideas related to nature and commonality would mesh with eco-communalism.
One challenge for urban designers and planners would be to judge how far their professions should push toward making a scenario come into beingsuch as policy reform or new sustainability -or to focus energy on creating resilient places that can cope with any of the futures. A long-term and more global view does provide an important filter, however. Can environments be adapted as populations age or resources become more constrained? Which of these models will use fewest resources if people choose to age in place? Is a gated enclave a blip when examined in a global perspective, just one end of a very long continuum of levels of enclosure, or the leading edge of a larger trend toward inequality (Grant and Mittelsteadt, 2004;Charmes, 2010)? Which of the current options for urban redevelopment, such as those indicated in Table 2, are most resilient?

Why the Global Suburban Future Matters
The twentieth century brought dramatic changes in cities and regions that resulted in the rise of the planning profession internationally, followed by the rise of the contemporary field of urban design (Ward, 2002;Birch and Silver, 2009). The twentyfirst century will have changes that equal, if not exceed, it in impact: populations that likely grow then decline, a substantially older population, environmental stress, and an ongoing tension between poverty and expectations of affluence. In a hundred years, of course, it is possible to change what seems to be normal or commonsense. People now expect to use motorized transportation to move around a citythat took far less than 100 years to achieve. With increasing life expectancies over the past century, the meaning of family has been dramatically reshaped; it will need to be again with suburban implications. There are cautionary tales from the history of design, however, of visionary changes that led to later problems.
These trends matter for urban design and planning globally. Planning and urban design have a long history of international transfer of ideas. For example, a century ago the Garden City idea developed by a British thinker drew on experiences in the United States and Australia and was fairly quickly transferred to built projects in Japan and continental Europe among other locations (Ward, 2002;Forsyth, 2005). More recently, the international influence of the Curitiba and Bogota examples of bus rapid transit shows how an idea that was implemented in a middle-income country became part of general knowledge elsewhere. For better and worse there are numerous other examples of such planning, design and policy transfers from new towns to open space preservation (Osborn and Whittick, 1977;Watson, 2009;Frenkel and Orenstein, 2012). Connections between different parts of the world are now very obviousfrom climate change to corporate investment. While each place is of course unique, these global links mean that around the world urban designers and planners are facing some similar challenges and where the challenges are different, it is important to fully understand those differences (Watson, 2009).
As comprehensive thinkers engaged with multiple public problems, urban designers and planners are well placed to deal with these issues as they relate to places. It can be hard for urban designers and planners to grasp the situation even within one country, let alone take a global perspective. However, the complex global nature of these topics challenges us to do just that, look beyond a traditional 'commonsense' to engage with global change in this transition century. this 'window' stage from 1950 until recently; Africa is not projected to enter it until after 2045 (UN, 2004, p. 2). 11 Of course in the twentieth century people have already changed their approach to aging dramatically (Costa, 1998;Bissonnette and van Soest, 2011). 12 Regionally there are a number of viable options from highly dispersed to highly concentrated urban formsalthough all are likely to be polycentric and have employment not only in the core.