Urbanization in the 21st century:
Challenges and opportunities for
environmental sustainability
Peter J. Marcotullio and Karen C. Seto
Global trends in urban population
(Source: UN DESA 2012)
Global trends in urban land use
• Current global urban built up area includes 73
million hectares.
• Urban expansion to 2030 may include an
additional 153 million hectares (Seto et al.
2011).
This translates to adding to an an area slightly larger
than the size of Texas, areas the size of another Texas,
California, Montana and Massachusetts
Challenges and opportunities with global
urbanization for environmental sustainability
• Challenges
– Direct impact on environment
• Habitat loss and fragmentation, agricultural land loss,
altered biogeochemical cycles and hydrology from the
creation of urban infrastructure
• Consumption of wood, cement, iron, steel, etc., for the
building of cities
– Provisioning deficient and up-grading
– Indirect impact related to increased consumption,
wastes and emissions from wealthy urban
residents
Global Urban Extent 2030
(Seto et al. 2012. PNAS)
Average (MgC/ha) and total C (PgC) loss
by region within pantropics
Total C loss across pantropics: 1.38 PgC ≡ 0.05 PgC yr−1
∼5% of emissions from tropical deforestation
(Seto et al 2012 PNAS )
Energy consumption with urbanization
Source: Jiang and Lin, 2012 Energy Policy 49(10)
Urbanization and direct materials consumption
+25%
Source:
Shen et al
2005 Cities
22(4)
+28% +41
+345%
+63%
+420%
+29%
+242%
Urbanization and direct materials consumption
Source:
Shen et al
2005 Cities
22(4)
Challenges of urbanization: Providing
infrastructure in the developing world
Informal residential development can be seen expanding into
agricultural lands on the fringe of Cairo, Egypt between 2002 (left) and
2010 (right). (Slide by S. Angel)
Challenges of urbanization: Providing
infrastructure in the developing world
Source: WHO / UNICEF 2012
More people have a mobile than a toilet
Challenges of urbanization: Providing
infrastructure in the developing world
Source: WHO / UNICEF 2012
More people have a mobile than a toilet
Challenges of urbanization: Aging infrastructure
in the developed world
Challenges and opportunities with global
urbanization for environmental sustainability
• Opportunities of urbanization
– Agglomeration economies in production and
consumption
– Low carbon transportation and energy
consumption
– Scaling benefits of increasing urban populations
Urbanization also bring opportunities: economic
productivity
Quigley 1998 Journal of Economic Perspectives 12(2)
Urbanization also bring opportunities: economic
productivity
Labor
productivity
increases by ~ 6
percent with a
doubling of
employment
density.
Source: Ciccone and Hall 1996 American Economic Review 86(1)
Urbanization also bring opportunities: consumer
cities
Glaeser et al 2001 Journal of Economic Geography 1(1)
Urbanization also bring opportunities: consumer
cities
Glaeser et al 2001 Journal of Economic Geography 1(1)
Urbanization also bring opportunities:
innovations
Inventions/person
increase by ~20
percent with a doubling
of density
Source: Carlino et al 2007 Journal of Urban Economics 61(3)
Urbanization also bring opportunities: Less
transportation carbon emissions
http://www.grida.no/
Urbanization also bring opportunities: Less
transportation carbon emissions
•
•
The literature suggests that doubling
residential density might lower
household VMT by about 5 to 12
percent, and perhaps by as much as
25 percent, if coupled with higher
employment concentrations,
significant public transit
improvements, mixed uses, and other
supportive demand management
measures.
Scenarios developed by the
committee suggest that significant
increases in more compact, mixeduse development will result in
modest short-term reductions in
energy consumption and CO2
emissions, but these reductions will
grow over time.
Urbanization also bring opportunities:
Thresholds for low-carbon transportation
Both light and heavy rail
require population
densities around stations to
be cost effective.
In the USA, at the observed average cost of $231 million and $53
million per mile, the average heavy-rail and light-rail systems in
cities need around 45 and 30 people per gross acre around
stations to achieve a high cost-effectiveness rating (Cervero and
Guerra 2011).
Urbanization also bring opportunities:
Thresholds for low-carbon transportation
3.1 SELECTING A SERVICE AREA
“HeatHigher
maps”
combine the following
use bike share stations tend to be located
in higher density areas (i.e. those areas with higher
variables:
population and job rates, and with higher levels of
Population
density
with high levels of pedestrian
activity), and
commercial
activity. Topography is also an important consideration
Employment density
related to servicearea siting. Implementation of a system
in jurisdictions with steep (or
be more complicated
mayProximity
to Universities
even rolling) terrain. Jurisdictions with steep slopes
bicycle
to the degree that this is possible,
want to consider,
mayAvailable
initial implementation in parts of the community that
infrastructure
are relatively at. Finally, the size of the service area will
Existing
of the jurisdiction.
sizetourist
on theto
be dependent
Proximity
locations
bike share programs in the U.S. that were part of this
area coverage of 1.5 square
include a service
analysis
Available
transit
miles (Spartanburg, SC) to 36 square miles (Washington
area).
DC Topography
33
Figure 15: Heat map analysis (City of Pittsburgh)
Source: Feasibilit y Study for a pot ential bike share program in the
city of Pittsburgh
34
Available bicycle infrastructure: Bicycle lanes,
Many bike share programs have developed “heat maps”
bike boulevards, cycle tracks and shared use paths
that help to de ne the initial service areas for the system.
Source:
US
DOT,
2012
provide supporting infrastructure for bike share
e following are typical factors in the development of
users and should be included in the analysis.37
these maps:
Urbanization also bring opportunities:
Thresholds for low-carbon transportation
Citi Bike hit 100,000 customer mark
in just 10 days after initiation of the
program. During this period, these
riders traveled more than 270,000
miles — greater than the distance to
the moon.
Source: Daily News, 2013
More compact urbanization brings lower energy
consumption and emissions
Life cycle assessment of 2 neighborhoods in Toronto
Source: Norman et al 2006 Journal of Urban Planning and Development 132(1)
Urbanization also bring opportunities: Lower
emissions…in highly urbanized systems
Africa
Urban
Non-urban
Asia
Urban
Non-urban
Latin America
Urban
Non-urban
Europe
Urban
Non-urban
North America
Urban
Non-urban
Oceania
Urban
Non-urban
World
Urban
Non-urban
Developing
Urban
GHG emissions
(tons CO2-eq./capita)
2.1
1.5-2.1
2.1-2.3
3.8
3.3-4.2
3.6-4.1
5.0
2.4-2.8
7.3-7.8
11.4
8.7-10.7
12.4-15.3
23.8
15.9-23.5
24.5-45.7
20.6
11.6-19.2
22.2-31.0
5.7
5.2-6.9
4.9-6.1
3.43
2.6-3.3
Source: Marcotullio et al Climatic Change
(under review)
Increasing urban population can bring
opportunities: Scaling functions
These results indicate that scaling is indeed a pervasive property of urban organization.
Source: Bettencourt, L., et al., 2007 PNAS 104(17)
Caveat: Efficiency gains can be overshadowed by the
scale of urban expansion
35% decrease
82% increase
(Guneralp and Seto. 2012. Applied Geography)
Caveat: Efficiency gains can be overshadowed by the
scale of urban expansion
More space
to cool
(Guneralp and Seto. 2012. Applied Geography)
Caveat: Efficiency gains can be overshadowed by the
scale of urban expansion
(Guneralp and Seto. 2012. Applied Geography)
Caveat: Efficiency gains can be overshadowed by the
scale of urban expansion
A 300% increase in annual CO2 emissions due
to concrete used in building construction.
A 25% decrease in energy required
per tonne of concrete in China.
(Guneralp and Seto. 2012. Applied Geography)
Future urbanization provides opportunities for
building better cities
(Seto et al. 2012. PNAS)
65% of the urban land cover on the
planet in 2030 have yet to be built