INTRODUCTION: CITIES AND THE URGENT CHALLENGES ■ 5metropolitan area, or a functional economic space. In many developing country
cities, the availability and reliability of data also present a challenge.
Th e chapter in this volume by Kennedy and others, “Greenhouse Gas Emis-
sions Baselines for Global Cities and Metropolitan Regions,” addresses these
issues directly and reviews existing methodologies and available published
results for various cities. Using a consistent, harmonized methodology, the
authors have calculated per capita emissions for more than 40 cities around
the world. Th is demonstrates that consistency and comparability are possible
and constitutes a seminal contribution to the joint eff ort among the United
Nations Environment Programme (UNEP), the United Nations Human Settle-
ments Programme, (UN-HABITAT), and the World Bank to advance an open,
international standard to measure GHG emissions from cities. Unsurprisingly,
the results reveal that per capita emissions tend to be higher in the cities of
industrialized countries compared with developing country cities. Further-
more, although these results show that per capita emissions in cities are gener-
ally lower than corresponding national per capita emissions, recent research on
U.S. cities suggests that when emissions embodied in materials consumed in
cities are taken into account, city per capita emissions are in fact very close to
national per capita emissions (Hillman and Ramaswami 2010).
Factors Infl uencing City Emissions
A variety of factors infl uence a city’s emissions profi le in complex ways. Th ese
factors include urban form and land use patterns, climate, building design and
technology, transport modes, and income levels. One would naturally expect
lower per capita emissions in a city with more energy-effi cient buildings, higher
rates of public transport use, or lower income levels. Th e relative importance of
such factors is explored by Croci and others in their chapter, “A Comparative
Analysis of Global City Policies in Climate Change Mitigation,” which includes
case studies of London, New York City, Milan, Mexico City, and Bangkok. Th e
authors identify income levels as a major factor in explaining the level of city
emissions, while also noting a number of methodological issues in calculating
emissions—Bangkok, for instance, estimates transport emissions from fuels con-
sumed within the city, whereas the other cities use vehicle-kilometers traveled.
Th e emissions profi les of cities can be very diff erent depending on specifi c
city contexts. Croci and others point this out clearly in their comparison of
cities across industrialized and developing countries. Th e largest contributor
to emissions in Bangkok is the transport sector, but in London and New York
City it is the buildings sector—specifi cally energy consumption in residential
and commercial buildings, with transport coming second. Bangkok’s climate,
income level, urban form, and transport systems are all factors that explain this