29

Does Urbanization Matter for Developing Long-term
Climate Scenario?
Shinji KANEKO1*, Satoru KOMATSU1, Phetkeo POUMANYVONG 1,
Latdaphone BANCHONGPHANITH1, Makoto CHIKARAISHI2 and Akimasa FUJIWARA1
1

Graduate School for International Development and Cooperation, Hiroshima University,
1-5-1 Kagamiyama, Higashi-hiroshima, Hiroshima 739-8529, Japan2
Department of Urban Engineering, The University of Tokyo,
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan*e-mail: kshinji@hiroshima-u.ac.jp

Abstract
Although cities already contribute to a large portion of global CO2 emissions and the significance of
localized counteractions and policies against climate change is recognized under the concept of polycentric
governance, urbanization has not been explicitly considered in most models used in constructing climate
scenarios. Its explicit incorporation into future climate scenarios would be most relevant in Asia where future
potential urbanization is enormous because of the region’s characteristics as a growth engine and as the mostpopulous region in the world. While reviewing the existing literature, this paper summarizes the relevant findings and arguments useful for exploring the possibility of proposing alternative methods of coping withurbanization when constructing climate scenarios. The study found that the available findings from individual
city-specific analyses at the micro scale and from cross-country analyses present seemingly contradictory
conclusions: the former appear to support the finding of improved efficiency reducing CO2 emissions withurban development; while the latter claim that urbanization leads to increased CO2 emissions at the national
level. This paper argues that the effects of urban density and the stage of development on the relationshipbetween urbanization and national CO2 emissions need to be studied further and the direct and indirect CO2
emissions of cities need to be elucidated to fill gaps in knowledge. The argument is also made that models
treating urbanization as a mediator and/or moderator may allow us effectively to separate the effects ofurbanization on energy use or emissions from those attributable to other socioeconomic factors.
Key words: carbon footprint, mediation, migration, moderation, urbanization

1. Introduction
Urbanization has been observed as a transitional
process of societal modernization involving multidimensional changes, particularly in social, economic and ecological dimensions. Socially and economically, it is aprocess of concentrating population and economic activity in areas defined as “urban” by each country. Ecologically, it is an expansion process of built-up areas thatinvolves land use and land cover changes, thereby affecting the functioning of ecosystems. To operationalize
urbanization, however, a demographic indicator, i.e., thepercentage share of urban population among the total
population, has been widely used. According to the UN(2010), almost 3.5 billion people were living in urban
areas in 2010, accounting for over half of the world’s
population. High concentrations of human and economic
activity are often associated with high levels of energy
consumption, a key driving force of carbon dioxide
Global Environmental Research
17/2013: 29-38
printed in Japanemissions (hereafter CO2 emissions). Cities and towns
consume an estimated 67% of global primary energy, andare responsible for 71% of energy-related emissions (IEA,
2008).
As one of the world’s most populous regions, Asia has
experienced the most rapid urbanization during the last
decade driven by better economic performance. This is
expected to continue further for at least a couple more
decades, as the share of urban population in Asia has justreached half the total, and hence it still has a large future
potential for urbanization. In fact, most of the additional
growth in the global urban population in the next four
decades will occur in Asia (UN, 2010). Moreover, many
extremely large cities are also located in Asia, and thenumber of such cities is also expected to increase.
Therefore, Asia is confronted with the problem of copingwith how to construct new cities and how to manage
existing cities properly from the perspective of climatechange.
©2013 AIRIES

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S. KANEKO et al.

Despite the aforementioned policy needs at the citylevel, apart from very recent literature such as O’Neillet al. (2012) and Shrestha and Shakya (2012), a limited
number of existing modeling techniques used inconstructing future climate scenarios have explicitly
considered the effects of urbanization on CO2 emission
trajectories. In exploring the possibility of proposing
alternative construction methods for climate scenarios
which explicitly consider the effects of urbanization, thispaper aims at reviewing existing literature and summarizing the issues which have relevance to further research.
In this paper, urbanization is defined solely on the basisof spatial properties, as most existing studies have done,to avoid confusion. More specifically, urbanization ismeasured by the percentage of the total populationaccounted for by urban dwellers.

2. Seemingly Contradictory Findings between
Two Perspectives
2.1 City growth, energy use and carbon emissions
Despite several challenges posed by urban development, it offers potential benefits to sustainable development as the increased concentration of people and theirrelated activities in relatively compact settlements may
bring the advantages of economies of scale in deliveringurban amenities and promote the efficient utilization ofnatural resources, thus minimizing the adverse effects ofconsumption and production on the environment (OECD,
2008; UNFPA, 2007). In fact, the IEA (2008) estimatedthat primary energy use per capita in cities in the UnitedStates, European Union and Australia was slightly lower
than their national averages. On average, city residents inthe European Union consumed 6% less primary energy
than the average European resident. In contrast, in China,
city residents consumed about 82% more than the
average Chinese resident in 2006 (IEA, 2008). Thisimplies that better forms of city development might leadto improved efficiency in energy consumption andconsequently lower carbon emissions.
Likewise, based on several published papers andcommissioned reports, Dodman (2009) observed that the
total CO2 emissions per capita of several wealthy European, North American, Latin American and Asian cities
appeared to be lower than their national average. For
North America, this difference was attributed mainly to
two causes. First, most of these cities have highly densebuilding forms with small average dwelling sizes, possibly requiring less energy to heat, light and cool than thosein suburban or rural areas. Second, they are equippedwith extensive public transport systems which reduce carownership levels below their national average. Nonetheless, it should be noted that the estimation results by the
IEA (2008) were for only the year 2006, while the findings by Dodman (2009) were obtained from a single-year
analysis in different periods with several uncertainties incity emissions accounting. While no benefits result fromcity growth or urban development automatically, careful
exploitation and planning are required (UNFPA, 2007).

2.2 Urbanization, national energy use and national
carbon emissions
When cities in a country develop and grow and eachof them improves its energy efficiency and mitigates its
carbon emissions, what are the overall impacts of thisphenomenon on national energy use and carbon emissions? The influence of urbanization on national energy
use and emissions has been increasingly examined using
various types of data (cross-sectional, time-series andpanel data) and methods (some studies have used energy
use or emissions per capita as their dependent variable,
while others have employed total energy use or emissions
as their dependent variable) in recent year. Jones (1991)
estimated the impact of urbanization on national energy
use per capita using cross-sectional data of 59 developing
countries in 1980, while Parikh and Shukla (1995) investigated the impact on both energy use and CO2
emissions per capita using a panel dataset of 78 developed and developing countries over the period
1965-1987. The results from both studies suggested thatwhile urbanization facilitated the transition from traditional fuels to modern fuels, it increased energy use andCO2 per capita. They attributed this positive correlation
mainly to an increase in direct and indirect transportenergy use, in energy intensive production and in accessto urban amenities as a result of urbanization. Some ofthese arguments were later supported by Holtedahl and
Joutz (2004), who conducted a time-series analysis for
Taiwan and found a positive correlation between urbanization on national electricity consumption per capita.
They further noted that urbanization implied increased
access to electricity and stocks of electric home appliances.1)
Like the energy use per capita analysis, a positive
correlation between urbanization and total energy use has
been reported by York (2007), who analyzed a panel
dataset of high-income countries, and by Jorgenson et al.
(2010), who studied a sample of developing countries.
The urbanization elasticity of national energy use fromthe former appeared to be noticeably higher than the one
from the latter. However, Liddle (2004) claimed thathighly urbanized societies were associated with low roadenergy use per capita. In relation with this claim, the IEA(2008) indicated that each urban dweller consumed 11%
less transport energy than the average US resident. This
seems to imply a negative correlation between urbanization and road energy use per capita. Nonetheless, thestudy by Liddle (2004) was based upon a relatively small
panel dataset of a single wealthy country at ten-year
intervals without controlling for economic activity
variables other than income, while the results from the
IEA (2008) were estimated only from data of the year
2006 with several assumptions.
Using total CO2 emissions data, many existing studies
show that urbanization influences national emissions
positively. For instance, based upon a panel dataset of 89
developed and developing countries over the period
1975–1998, Cole and Neumayer (2004) concluded thaturbanization increased national emissions because ofDoes Urbanization Matter for Developing Long-term Climate Scenario?

high pollution-intensive behavioral patterns of urban
residents. The findings are also supported by recent
studies by Menz and Welsch (2011), who found a positive correlation between urbanization and national emissions for a sample of 26 OECD countries during the years
1960-2005. They further noted that the positive correlation could be due to the notion that urbanization is a
proxy for low-density settlements of wealthy countries,
which are often associated with energy-intensive behavior. Similarly, Jorgenson and Clark (2010) suggested thaturbanization increased national emissions in both developed and developing countries. In a time-series data
context, Alam et al. (2007) found that urbanization had
contributed to an increase in Pakistan’s emissions per
capita. Using national data over the period 1992-2009, Li
et al. (2011) also concluded that there was a positive
correlation between urbanization and national emissions
for China.

3. Clues to Filling the Gap
3.1 Does urban density matter?
It has been observed that as populations of cities grow,so do the cities’ areas. In many cases, the growth of thelatter tends to be faster than the growth of the former(Angel et al., 2005; Hankey & Marshall, 2010), possibly
implying that urbanization contributes to urban sprawl ora decline in urban density (population/urban built-up
areas). This could pose a greater challenge to mitigating
CO2 emissions. Over the past two decades, considerable
efforts have been made to study the relationships among
urban density, energy use and emissions in various sectors, particularly transport and residential sectors. Usinga simple regression and a sample of 32 large, wealthy
cities in 1960, 1970 and 1980, Newman and Kenworthy(1989) found a negative correlation between urban density, road energy use and emissions per capita. Theysuggested that high urban density helped reduce car dependency, promoted the use of public transport andshortened travel distances. A similar conclusion was
drawn by Ewing et al. (2008) and Karathodorou et al.
(2010). However, this general conclusion is not freeof criticism. After reinvestigating Newman and
Kenworthy’s data using clustering and the Co-Plot technique, Mindali et al. (2004) suggested that there was nodirect correlation between overall urban density (population/built-up areas) and road energy use per capita.
Instead, the negative correlation seemed to be due toother density attributes such as inner area density andcentral business district employment density. Similarly,
Bento et al. (2005) noted that urban household vehicle
miles traveled per vehicle were influenced by population
centrality, job distribution, city shape and road density.
In the residential sector, high urban densities could
possibly imply large economies of scale in deliveringurban amenities and compact residential building forms,
which tend to be associated with less exposed wall areaand less heat loss through the roof or floor (Chen et al.,2008). Applying the correlation matrix technique to data31

on 45 core Chinese cities in 2002, Chen et al. (2008)
found that urban density helped reduce household natural
gas and electricity consumption per capita, while it
increased air pollution and noise and reduced green space.
Based upon US household survey data from 50 states anda multivariate analysis, Ewing and Rong (2008) also
showed that average residential energy use per householdin compact counties was significantly lower than in
sprawling ones because of attached housing and smaller
dwellings. In addition to the residential sector, Lariviereand Lafrance (1999) suggested that there was a moderately negative correlation between urban density andannual city electricity consumption (excluding electricity
used in the industrial sector) per capita in Canada. Usinghousehold survey and prefectural-level data, input-output
and multivariate analyses, Lenzen et al. (2006) found thathigh population density negatively influenced total
household energy requirements per capita in Australia,
Brazil and Japan, whereas total household energy
requirements per capita appeared to be higher in metropolitan areas of India than in her non-metropolitan areas.
Despite some disagreements, city growth or urban
population growth is likely to increase city energy use
and CO2 emissions because urbanization appears to contribute to a decline in urban density. Therefore, formulating policies and strategies to mitigate urban sprawl orreverse the current development trend deserve greaterattention.
3.2 Does the development stage matter?
Urbanization is driven by natural population growthin urban areas, changes in administrative boundaries andnet rural-to-urban migrations. Various empirical findingssuch as Kojima (1996) and Tiwari (2008) suggest that
migration plays an important role in promoting urbanization in developing countries. The share of net rural-tourban migration on urban population growth in Asia has
increased from 40.4% in the 1960s to 46.7% in the 1970s
and 63.6% in the 1980s (Skeldon, 1998).2)
In developing countries, rural-to-urban migrants areconfronted by relatively large differences in accessibility
and availability of energy resources before and after theirmigration, hence they significantly alter the patterns ofresidential energy consumption compared to those indeveloped countries. Rural residents commonly depend
more on traditional biomass-origin fuels such as
firewood, straw, and animal dung, depending on the surrounding natural conditions. Contrarily, natural resources
are less available in urban areas but modern energy
sources such as kerosene and LPG (Liquefied Petroleum
Gases), which are produced from fossil fuels are moreeasily attained. Cai and Jiang (2008) compared residential energy consumption in rural, peri-urban and urban
areas of China and concluded that urbanization resulted
in a shift in energy structure from traditional biomasses tocommercial fossil fuels at a macro scale. Strong dependence on traditional energy resources in rural areas andmore reliance on modern energy in urban areas are also
reported in other developing countries such as India

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(Ekholm et al., 2010) and Bangladesh (Miah et al., 2011).
Besides energy accessibility, changes made byrural-to-urban migrants extend to various aspects of lifestyle. In most cases, the migrants successfully increase
their cash income for a certain period of time after
migration, while their family size decreases. Moredependency on electric home appliances and modern
cooking devises is accelerated as a result of increased
income, leading to more fossil energy consumption andcarbon emissions. On the other hand, changes in family
size influence the efficient use of energy on a per capita
basis. Using micro-level surveyed data in India, Pachauri(2004) indicated that an increase in the number ofhousehold members reduced the per capita total household energy requirements. This implies that householdenergy consumption becomes less efficient with migration.
Regarding the relationship between energy consumption and energy access, resource endowments and lifestyle, the “energy ladder model” gives theoretical underpinnings for examining changes in household energy use
through urbanization. Heltberg (2004) noted that theenergy ladder model conceptualized fuel choice into
three phases. In the first phase, residents universallydepend on biomass resources and in the second, households switch their fuels to “transition” fuels such as
kerosene, coal and charcoal in response to higher household income, urbanization and biomass scarcity(Heltberg, 2004). In the final phase, households switch
further to LPG, natural gases or electricity for cooking(Heltberg, 2004). The empirical evidence suggests the
major factor encouraging households to move up theenergy ladder is primarily the affluence of the households
as measured by income or expenditures (e.g., Hosier &Kipondya, 1993; Sovacool, 2011; Davis, 1998), but resource availability (e.g., Peng et al., 2010; Sovacool,2011), and the relative price of respective fuels (Hosier &Kipondya, 1993; Peng et al., 2010) also influence thechoice of energy resources. Therefore, households do notmonotonically climb up the energy ladder with income
level. Empirical evidence suggests that more modern
fuels are consumed by relatively affluent segments ofhouseholds but firewood is still used by richer families(Hiemstra-van der Horst & Hovorka, 2008; Bensel &Remedio, 1995) although firewood utilization is notnecessarily the same among the rich and poor; the poor
require it as a general and basic need whereas the rich use
it for special purposes such as barbeques and space heating. Heltberg (2004) concluded that fuel use resembled aportfolio menu choice in which households used both
high- and low-cost items depending on their budgets,
preferences and needs. This indicates different implications of migration (urbanization) on changes in energy
use and carbon emissions between developing anddeveloped countries. This would pose a clue as to how to
see the impacts of urbanization differently elucidated
according to stage of economic development in order tofill the knowledge gap in the seemingly contradictory
mixture of findings.

To date, very few studies have rigorously investigateddifferent potential implications of urbanization for energy use and emissions at different stages of economic
development. Different levels of development imply
different energy compositions, different lifestyles, anddifferent levels of access to urban infrastructure andamenities, energy efficiency, vehicle ownership andurban density. These differences are likely to cause theinfluence of urbanization on energy use and emissions tovary across countries at different stages of development.
Our suspicions are indirectly reflected in some existing
literature. For instance, York (2007) reported that theurbanization elasticity of national energy use was 0.53
for a sample of 14 wealthy European countries, while
Jorgenson et al. (2010) illustrated that the elasticity was
0.369 for a sample of 57 less developed countries,
Regarding national emissions, based upon a sample of 88
developing countries, Martínez-Zarzoso and Maruotti(2011) argued that there was an inverted U-shaped
relationship between urbanization and national emissions.
In contrast, using a sample of 26 OECD countries, Menz
and Welsch, (2011) found that the urbanization-emissions elasticity was linearly positive (0.31).
The empirical evidence of differential impacts ofurbanization on national energy consumption and emissions has been further substantiated in two recent studies,
Poumanyvong and Kaneko (2010), and Poumanyvong
et al. (2012) (see Fig. 1). The former systematicallyinvestigated the effects of urbanization on nationalenergy use and emissions using a sample of low, middle
and high income countries over the period 1975-2005,
while the latter used a similar sample and method, but
focused on the transport sector. Poumanyvong and
Kaneko (2010) found that the effects of urbanization on
national energy use and emissions varied across thestages of development. It reduced energy use in low
income countries, while it increased energy use in middle
and high income countries. To a large extent, a large
positive elasticity coefficient of energy use with respect
to urbanization in high-income countries seems to beconsistent with the study by York (2007), while a negative correlation in low-income countries likely relates toefficiency gains from fuel switching (i.e., from biomass
to modern fuels) as a consequence of urbanization. The
influence of urbanization on national emissions also differs, but is positive for all the income groups. In highincome countries, a 1% increase in urbanization raises
national emissions by 0.358%. This elasticity coefficient
is lower than that of the other income groups, but it isvery close to the one obtained for a sample of OECD
countries by Menz and Welsch (2011).
Similarly, the impact of urbanization on transport androad energy use varies among low-, middle- and highincome countries (Poumanyvong et al., 2012). The
urbanization elasticity of national transport and roadenergy use in high-income countries tends to be noticeably greater than that in the other groups. This can possibly be attributed mainly to the fact that high-income
countries have higher levels of vehicle ownership, larger

Does Urbanization Matter for Developing Long-term Climate Scenario?

shares of private motorized modes, and lower levels ofurban density with a faster rate of sprawl compared withthe other groups. Furthermore, it has been observed thatthe average weight and engine power of new cars in several high-income countries have risen in recent years(Schipper, 2011). This not only offsets efficiency gained
from technological progress, but also potentially increases energy use. Surprisingly, the urbanization-road
energy use elasticity in middle-income countries appears
to be smaller than that in low-income countries. Thisphenomenon may occur for some of the following
reasons. First, middle-income countries are currently inthe process of public transport development, while
low-income countries are shifting from non-motorized
towards motorized modes. Second, the average annual
decline rate of urban density in low-income countries isfaster than that of middle-income countries. For instance,
between 1990 and 2000, the average annual decline rateof urban density in the former was 2.5%, while in thelatter it was only about 1.5% (adapted from Angel et al.,2005). It is worth noting that the results of the urbanization-transport energy use relationship can be generalized

Fig. 1 A summary of urbanization (percentage of urban
population) elasticities of national energy use (a) andemissions (b) (adapted from Poumanyvong & Kaneko,
2010; Poumanyvong et al., 2012).

33

to the urbanization−transport emissions relationship, as
energy used in the transport sector is highly homogenous(i.e., the share of petroleum products in the road energy
use is over 95%).
3.3 Carbon accounting of cities as open economies
In the last several years, data on CO2 emissions from
cities and regions have become available through either
research articles or documents/websites of municipal
governments. For example, the former includes Brown
et al. (2008) for one hundred large municipal areas in the
US; Dhakal (2009) for four megacities in China: Beijing,
Shanghai, Chongqing and Tianjin; Gomi et al. (2010) for
Kyoto; Phdungsilp and Dhakal (2009) for Bangkok; andthirteen global cities by Kennedy et al. (2009) among
others, examples of which include MOEWR (2008) for
Singapore, TMG (2007) for Tokyo, BMA (2007) for
Bangkok, PLANYC (2007) for New York, London(2007) for London, and Chicago (2008) for Chicago.
Although these estimates fundamentally follow theterritorial principle of the IPCC Guidelines for Greenhouse Gas Inventories and hence account for CO2 emissions from their administrative boundaries, indirect CO2
emissions embedded in electricity and heat are considered in most cases. Cities, however, have open
economies with intensive cross-boundary linkages formoney, services, goods, materials and humans. Changes
in cities quickly and vigorously spill over into the outside
world. Cities are also at the frontier of industrial transformation, which typically follows the pattern known as
Petty-Clark’s law from an agrarian economy to a service-oriented one passing through manufacturing industries. This implies a shift from a production-oriented
economy towards a consumption-oriented one, whichlargely depends on and induces indirect CO2 emissions
embodied in the commodities imported to meet thedemand in cities.
The degree of external dependency of cities can beevaluated by their ecological footprint, which is estimated to be 180 times greater than its land area for Vancouver as an example (Rees & Wackernagel, 1996).
Similarly, the ecological footprint for London required
for food and forest products and carbon assimilation was
120 times greater than the area within its administrative
boundaries in 1995 (IIED, 1995) and worsened to 293
times in 2000 (IWM, 2002). This is generally applicableto the issues of energy consumption and CO2 emissions,although empirical evidence is very limited. While there
is a large volume of published literature on embodied
energy, comparing direct and indirect energy using input-output (I-O) economic tables, material flows and life
cycle analyses for whole economies and for specificsectors and products, their application to the evaluationof energy and carbon footprints of cities is rarely madeexcept for a few cases in the past (Shulz, 2010; Lenzen
et al., 2004; Troy et al., 2003).
When cities are developed, their external dependencies on carbon emissions increase whereas even direct
carbon emissions in cities decrease. More empirical

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S. KANEKO et al.

studies on direct and indirect CO2 emissions of cities
from these perspectives can fill the gap in our knowledge
on these seemingly contradictory findings. Furthermore,
the need for further studies is supported from the viewpoint of policy perspectives. In the policy community,
carbon emissions or the carbon footprint still means the
direct emissions plus emissions embedded in electricity
and heat only, despite the material and ecological footprints of cities being well acknowledged. From the management viewpoint, it is also a matter of accounting
systems whether to allocate emissions at point of consumption or point of production for efficient management. It is also a matter of allocating responsibilities
whom we should make responsible for what with regard
to urban carbon. The question of responsibility is
being debated in many publications (see IEA, 2008;
Satterthwaite, 2008) and policy forums recently and there
have been informal calls to develop a common reportingand evaluation system for cities. The bottom line of any
debate is that material uses, urban lifestyles, extent ofenergy uses, and CO2 emissions are all closely interrelated; therefore, due attention by city authorities fortheir upstream emissions impacts can greatly help toalleviate the burden of large CO2 cutbacks at the point of
production.

4. Urbanization as Mediation or Moderation
Effects
It is known that there are three different types of
causal assumptions: direct causal effect, mediated causal
effect, and moderated causal effect (Wegener & Fabrigar,
2000). Most existing studies mentioned above have assumed that urbanization directly contributes to carbon
emissions, where “urbanization” is defined using spatial
indicators such as urban population (% of total) and urban densities. On the other hand, when the urbanization isdefined solely on the basis of such spatial properties, theassumption of a direct cause-effect relationship between
urbanization and carbon emissions inevitably involves
problems of distinguishing between socioeconomic actors and urbanization. This is because, in principle, thedirect factor causing carbon emissions is human activities
rather than the spatial conditions of cities/countries, andthus spatially-defined urbanization should be regarded as
an approximate indicator of human activities that may beaffected by spatial conditions. To avoid such approximation, we may have to (1) look for more appropriate
urbanization indicators which reflect changes in humanactivities caused by changes in spatial conditions, or (2)clearly deal with interactions between spatially-definedurbanization and human activities. Because the first
option might be unrealistic in empirical analysis due todata limitations, this section focuses on the second option
and revisits the relationships among urbanization, humanactivities and carbon emissions from the viewpoint ofdeveloping a long-term climate scenario. As indicated in
the introduction, urbanization must be defined solely on
the basis of spatial properties to be consistent with mostexisting studies.
In general, a direct causal effect is employed when the
independent variable can be assumed to affect the dependent variable directly. On the other hand, a mediatedcausal effect is introduced when an analysis attempts to
identify the intermediary process that leads from theindependent variable to the dependent variable (Muller
et al., 2005). Or more simply, under the assumption ofmediation causal effect, the independent variable is presumed to determine the mediator, and in turn, the mediator determines the value of the dependent variable (Wu &Zumbo, 2008). For example, it can be expected thaturbanization causes changes in human activities, andchanges in human activities affect carbon emissions. On
the other hand, a moderated causal effect is introduced
when an analysis attempts to identify a modification
process in which a moderator adjusts the strength ordirection of a causal relationship between the independent variable and dependent variable. For example, it canbe expected that even identical economic activities cancause different amounts of carbon emissions dependingon the urbanization level, i.e., urbanization can moderate
the links between human activities and carbon emissions.
Both mediated and moderated effects are often referred
to as third variables, since these variables are placedin between the dependent variable and independent
variable.
Considering these three cause-effect relationships, we
could assume at least five possible cause-effect relationships among urbanization, human activities, and carbon
emissions (Fig. 2): (A) Urbanization as a direct influential factor, (B) Human activities as a mediator, (C) Urbanization as a mediator, (D) Human activities as a moderator, and (E) Urbanization as a moderator. The question
here arises of how to choose the appropriate cause-effectrelationship. Regarding this, Wu and Zumbo (2008) gave
an important insight. They pointed out that cause-effectrelationships are distinct in concept and design, and thus
the appropriate role of each variable in the wholemodeling system should be determined primarily by the
researchers’ substantive theory and appropriate operationalization, rather than by some statistical testing.
As mentioned above, theoretically the direct influential factor affecting carbon emissions is human activities,
not urbanization. Specifically, urbanization defined byspatial population distributions and urban boundaries
might be a contextual or background factor, rather than adirect influential factor. In this sense, cause-effect relationships (A), (C), and (D) are assumed, where the direct
urbanization impacts carbon emissions, and are kinds ofsimplified relationships where the process and mechanisms of urbanization are not taken into account. The
next question is whether the assumption of such directcause-effect relationships is oversimplified or not. The
answer might depend on the purpose of the analysis. For
example, if our research question is “whether there is acertain impact of urbanization on carbon emissions ornot,” then such simplification may be acceptable. On theother hand, when we try to develop a long-term climate

Does Urbanization Matter for Developing Long-term Climate Scenario?

scenario, some theoretical explanations on the process
and mechanisms of urbanization may certainly berequired. For example, the following research questions
may become more important: (1) Does urbanization
increase the amount of economic activities? (2) Does
urbanization change industry structure? (3) Does urbanization increase the environmental efficiency of economic
activities? And, (4) Does technological innovation become more important along with the advancement ofurbanization to reduce carbon emissions? The first andsecond questions can only be examined by introducing
cause-effect relationship (B), and the third and fourthquestions can only be examined by introducing causeeffect relationship (E). At least it is certainly necessary toconfirm whether such mediated or moderated effects ofurbanization exist or not and whether or not they are
relevant to the development of long-term climate scenarios, before choosing one of these cause-effect relationships. However, few studies have focused on the
mediation and/or moderation effects of urbanization.
Developing relevant methodologies and accumulating
empirical results are important future tasks to beconsidered.

5. Concluding Remarks
If we can construct new cities and manage existing
cities in more climate-benign ways collectively, howmuch change in the future pathways of overall CO2
emissions can be expected? In order to find some clues tothe answer of this rather big question, this paper summa-

35

rizes what can be learned from past experience in theliterature and identifies future research agendas.
First, the available findings from city-specific analyses at the micro scale and those from cross-country
analyses present seemingly contradictory conclusions:the former support efficiency improvements in CO2emissions with urban development; while the latter claimthat urbanization leads to an increase in CO2 emissions at
national level. Much knowledge and empirical evidence
need to be accumulated to account consistently for thoseconclusions. In particular, for better climate policies in
Asia, where future urbanization will have great potential
to affect emissions scenarios, such research would be
beneficial. We argue that such examples include themarginal effects of rural-urban migration on CO2 emissions, the effects of development stage on the relationship between urbanization and national CO2 emissions
and direct and indirect CO2 emissions of cities.
We also propose that models treating urbanization asa mediator and/or moderator may allow us effectively toseparate the effect of urbanization on energy use and CO2
emissions from that attributable to other socioeconomic
factors. If it can be properly done, we believe it will bepossible to step further from empirical studies of the past
to the future scenario development. However it should be
acknowledged that empirical analyses are restricted inapplication to relatively shorter scenario constructions,where the future is highly path dependent on the previous
trends, so they cannot be used to develop longer-term
future scenarios where prescriptive or normative changes
are assumed.

Fig. 2 Possible cause-effect relationships among urbanization, human activities, and carbon emissions.

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Acknowledgements
We would like to thank the two referees for theirconstructive comments and suggestions for improving
the quality of our manuscript. This research is supportedby the Environment Research and Technology Development Fund (S-6) “Establishing of Methodology to
Evaluate Middle to Long Term Environmental Policy
Options toward Asian Low-Carbon Society” from the
Ministry of the Environment, Japan.
Notes
1)

2)

The discussion of the effect of urbanization on energy use by
Holtedahl and Joutz (2004), and Parikh and Shukla (1995)
seems to capture partially the effect of changes in income after
migration to urban areas. Nonetheless, Jones (1991) argued that
although urbanization coincided with economic development,
it exerted an independent influence on energy consumption.
The numbers are calculated from total effects of natural growthand net-migration, and the effect of reclassification of administrative areas is omitted because it is difficult to identify theeffects of reclassification quantitatively (Skeldon, 1998).

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Shinji KANEKO
Shinji KANEKO graduated from Kyushu University, Japan, and obtained his Doctorate in Engineering in 2001. He is now a Professor and Associate
Dean of the Graduate School for International
Development and Cooperation, Hiroshima University. Since 2005, he has also served as a START
Research Fellow at the Global Change SysTem for
Analysis, Research and Training (START) in the US. He has also served asa Research Fellow at the LBJ School, University of Texas, Austin, since2008, and a Visiting Professor at Beijing Normal University since 2010. He
has worked as an external evaluator for the post-evaluation of ODA projects
in Japan. He has authored many papers in international journals for which
he also serves as a reviewer. He has been awarded paper prizes from theJapan Society of Civil Engineering. He serves as an Editorial Board
member for Environmental Policy and Governance and several otherdomestic societies. His research interests revolve around environmental
and resource economics and energy-related issues, including climatechange, input-output analysis, renewable energy, urban air pollution andwater resource management, mainly in the Asian region.
Satoru KOMATSU
Satoru KOMATSU graduated from Hiroshima
University, Japan, and earned his Ph.D. in March
2009. He is now working as an Assistant Professor
at the Graduate School for International Development and Cooperation, Hiroshima University. In
the past, he has worked at the JSPS (Japan Society
for the Promotion of Science) as a research fellow(DC), and at the Graduate School for International Development andCooperation, Hiroshima University, as a Post-Doctoral Research Associate.
Currently he is serving as a reviewer for journals such as Energy Policy,
Environment Development, Sustainability, and others. His research interests include economic evaluation of the environment and natural resources,
evaluating rural electrification policies using solar photovoltaic energy indeveloping countries, and sustainable urban development in Asian megacities.

38

S. KANEKO et al.
Phetkeo POUMANYVONG

Akimasa FUJIWARA

Phetkeo POUMANYVONG received his Ph.D. from
Hiroshima University in 2011 under the supervision of Professor Shinji Kaneko. His doctoral
dissertation was entitled “Impacts of Urbanization
on National Energy Use and CO2 Emissions: A
Cross-country Analysis.” After graduating, heworked as a Research Associate in a project
entitled “Establishing Methodology to Evaluate Middle- to Long-term
Environmental Policy Options toward an Asian Low-Carbon Society(S-6),” funded by the Ministry of the Environment, Japan, from April 2011
to March 2012. Since then, he has been working at Hiroshima University as
an Assistant Professor for the Global Environmental Leaders Education
Program for Designing a Low-Carbon World. His primary researchinterests include demographic change, urbanization and their implications
for energy consumption and climate change.

Akimasa FUJIWARA graduated from Hiroshima
Unjiversity, Japan, in 1983 and obtained his
Doctorate of Engineering in 1993. He is now a
Professor and the Dean of the Graduate School ofInternational Development and Cooperation,
Hiroshima University. He serves as Chairman of
the International Scientific Committee of the Eastern Asia Society forTransportation Studies, and is an acting member of the Transport Research
Board, the Association for European Transport, the International Association for Travel Behavior Research, the World Conference on Transport
Research Society and several domestic societies in Japan. He is also a
reviewer for journals such as Transportation, Transportation Research
Record, and others. He is actively involved in academic and management
units such as the Engineering Ethics Education Committee of the JSCE andthe City Planning Council of Hiroshima City as a Chairperson, and the
JABEE Committee of the JSCE and the Transport Policy Council of the
MLIT as a member. He was awarded the Yasoshima Prize (Best Paper
Prize) of the Eastern Asia Society for Transportation Studies. His researchinterests cover a range of traffic and transport-related areas, includingtransportation planning and policy evaluation, activity-based travel demandmodeling, sustainable urban and regional development, and evaluation/
design of innovative urban and transportation policies. He has authoredmany papers in related fields which were published in reputed internationaland national journals.

Latdaphone BANCHONGPHANITH
Latdaphone BANCHONGPHANITH was bornin Vientiane, Laos. She was awarded a
Monbogakusho Scholarship to continue her
graduate studies at the Graduate School ofInternational Development and Cooperation,
Hiroshima University, in April 2005. She conducted research on virtual water and its economicand environmental implications in Beijing in her Ph.D. courses andreceived her doctorate in March 2010. After graduation, she worked as a
research fellow for the project of “Establishing Methodology to Evaluate
Middle- to Long-term Environmental Policy Options toward an Asian
Low-Carbon Society (S-6),” funded by the Ministry of the Environment,
Japan, based at the Graduate School of International Development andCooperation, Hiroshima University. Her main responsibilities in the project
were to deal with carbon inventories in three Asian mega-cities: Beijing,
Shanghai and Jakarta, bu applying environmental input-output model. In
April 2012, she returned to her home country, Laos, after shi finished her
contract with the project.
Makoto CHIKARAISHI
Makoto CHIKARAISHI received his Ph.D. at theGraduate School for International Development
and Cooperation, Hiroshima University, under
Professor Akimasa Fujiwara’s supervision in
March 2010. His doctoral thesis was entitled“Changes in and Variations of Acitivity-Travel
Behavior.” His major research interests include
travel behavior modeling, travel survey designs, mobility issues of seniorcitizens, and uncertainty in transportation planning. From April 2010 toMarch 2012, he was working at Hiroshima University for the Global
Environment Leaders Education Program for Designing a Low-Carbon
World. Since April 2012, he has been a JSPS post-doctoral research fellow(PD) at the Department of Urban Engineering, the University of Tokyo.

(Received 18 July 2012, Accepted 20 November 2012)