1. Determinants of cities’ emissions: a comparison of seven global cities
3rd International Scientific Conference on
“Energy and Climate Change”
Athens
7th-8th October 2010
Edoardo Croci

2. Context
Significant contribution of major cities to global GHG emissions, in particular of carbon dioxide
(UNEP, UNHabitat, 2005: urban activities responsible for 80% of global CO2)
Differences in urban absolute/per capita emissions among cities from industrialized and developing countries (and within each “category”)
Increasing voluntary commitment of city governments to emissions reduction targets

3. Research questions - Which basic factors underlie urban emissions?
- Which urban features interact in influencing these factors…
…and can be considered as ultimate determinants of emissions?

4. Choice of case studies Criteria:
focus on global cities (at least population > 1 million)
availability of detailed emissions inventories
availability of data on selected urban indicators
representitiveness of different world areas (climate; economic performance)
-> Bangkok, Chicago, London, Madrid, Mexico City, Milan, New York City
Main bias: consistency of urban data used (methodology; territorial coverage)
-> definitions of urban areas may differ among countries and accordingly to criteria used

5. Methodology -> Focus on residential emissions and ground transport
Data availability
Two main sectors in most of urban inventories
Steps:
1) Disaggregation of emissions into main factors
(emissions factors; activity data)
2) Analysis of emissions determinants
qualitative comparison + quantitative indicators on urban features such as: climate, morphology, infrastructure, technology, economic activities in place, income, prices, culture…

6. Main factors: Built sector
Eb = emissions from energy used in buildings
Qi = quantity of “i” fuel consumed directly for various purposes (i.e. heating, water heating, cooking...) for unit of built surface (kWh/m2)
EFi = emission factor of “i” fuel (CO2/kWh)
Si = floor space consuming “i” fuel (m2)
f = 1, … 8
1 = natural gas
2 = oil
3 = LPG (Liquefied Petroleum Gas)
4 = coal
5 = waste used as fuel
6 = biomass
7 = energy from renewable sources
8 = other
Qe = quantity of electricity consumed for various purposes (i.e. heating, water heating, cooking, air conditioning, use of electric appliances...) for unit of built surface (kWhe/m2)
EFe = emission factor of electricity purchased in the city (CO2/kWhe)
Se = floor space consuming electricity (m2)

7. Main factors: Built sector
Residential sector:
- significant differences in fuel and electricity consumption per housing unit (e.g. Chicago, highest values; Bangkok, Mexico City, lowest values)
emissions factors have secondary relevance (apart from E.F. of electricity)
Qi = fuel consumption
(kWh/housing unit)
Qe= electricity consumption
(kWh/ housing unit) Qi Qe
Qi+Qe
Bangkok
(2005)
1.194 
4.657
5.851
Chicago
32.224
5.751
37.975
London
(2003)
18.056
4.418
22.474
Madrid
8.766
3.249
12.015
Mexico City
(2000)
4.369
1.391
5.759
Milan
15.275
2.375
17.649
New York City
14.283 
 6.319
20.602
EF. e.e.
(gCO2/kWh)
Bangkok
509
Chicago
664
London
430
Madrid
404
Mexico City
684
Milan
311
New York City

8. Main factors: Ground transport
Where:
Tj = number of passengers’ trips with “j” mode
Lj = average length of a single trip with “j” mode (passengers km)
lf = load factor of “j” mode (n. passengers/vehicle)
EFji = emission factors of “i” fuel with “j” mode (gCO2/vehicle km)
f = 1, … 6
1 = gasoline
2 = diesel
3 = LPG
4 = electricity
5= other
6 = no fuel
VKTzi = kilometres travelled by freight vehicles of “i” fuel and of “z” mode (vehicle km/inhabitants)
EFzi = emission factors of “i” fuel with “z” mode (gCO2/vehicle km)
z = 1,…3
1 = light duty vehicles (and sub-categories)
2 = heavy duty vehicles (and sub-categories)
3 = rail
m = 1, … 6
1 = foot
2 = bicycle
3 = subway/rail
4 = bus
5 = passenger car
6 = motorcycle

9. Tj (number of passengers trips per inhabitants per year)
Main factors:
Ground transport
Ground transport:
relevant role of private cars (Chicago) and freight (Chicago; Bangkok) in cities with higher emissions
relevant role of non-motorized modes (New York City) and public transport (London; Madrid; Mexico City) in containing emissions
Passengers transport
Tj (number of passengers trips per inhabitants per year)
Year
Foot
Bicycle
Subway/rail
Buses
Pass. Cars
Motorc.
Bangkok
2005
14% - 3%
37%
46%
Chicago
2001 5% 1% 6%
88%
London
2003
21%
18%
16%
44%
Madrid
26%
0,3%
22%
51%
Mexico City*
2002
64%
Milan
10%
19%
12%
50%
New York City
*For Mexico City data on foot/bicycle trips are not available

10. Main factors: Ground transport
significant differences in the carbon intensity of the private and commercial vehicle stock
e.g. Bangkok: very inefficient public and commercial fleet
Chicago: carbon-intensive stock of passenger cars
London, Milan: very low carbon intensity for passenger cars
Year
Buses
(gCO2/km)
Pass. Cars
Bangkok
2005 -
Chicago
579
London
2003
1200
176
Madrid
Mexico City
2004
800
377
Milan
1398
212
New York City

11. Main determinants Built sector
Residential emissions:
climate, primary determinant: entails more relevant energy consumption levels for those cities having higher heating needs (e.g. Chicago, London, New York City) or cooling needs (Bangkok, as emerges from electricity consumption levels).
Qi (kWh/ h.u.)
HDD
Chicago
32.224
3.610
London
18.056
2.679
New York City
14.283 
2.641
Milan
15.275
2.157
Madrid
8.766
1.891
Mexico
City
4.369
584
Bangkok
1.194 
Qi = fuel consumption
(kWh/housing unit)
HDD= Heating Degree Days

12. Main determinants: Built sector
- features of the residential stock:
cities with a dense built environment consume lower energy quantities per housing unit
better energy efficiency relevant in explaining lower energy consumption level
- level of economic welfare: determinant for electricity use
Qi+Qe
Density
(p/ha)
New York City
20.602
104
Chicago
37.975 15
GDP p.c. (000$)
Qe (kWh/h.u.)
New York City
52,8
6.319
London
46,2
4.418
Madrid
29,0
3.249
Mexico City
14,3
1.391

13. Main determinants: Ground transport
Ground transport emissions:
form and density, primary determinant shaping modes in use and emissions:
high density: relevant quota of passenger demand satisfied through non-motorized transport (New York City) and public transit (New York; London; Mexico City; Milan)
lower density: significant use of private cars and higher emissions (e.g. Chicago)
Car
trips
Foot
Density
(p/ha)
Mexico City
236,1
n.a.
125
New York City
310,3
708,1
104
Milan
637,8
131,0 72
Madrid
508,4
255,5 56
London
554,0
272,0 55
Bangkok
313,8
95,5 36
Chicago
929,4
58,4 15

14. Main determinants: Ground transport
Ground transport emissions:
- technology and features of vehicle stock: determinant for cities where the stock is very inefficient (e.g. Bangkok) or very efficient (e.g. Milan).
Average age of fleet
(n. years)
Emissions
Transport
(tCO2/per capita)
buses
passenger
cars
trucks
Bangkok
3,74
14 (local)
7,5 (local)
12 (local)
Milan
1,10
6,3 (local)
8,8 (national)
7,2 (local)

15. Future research
need to collect more specific data at city level in order to support observations
e.g. built sector:
- typologies of housing units and commercial buildings
- heating/cooling systems in operation within the city
diffusion of electric appliances in households/offices and average energy efficiency
e.g. ground transport:
more detailed insight into the vehicle stock (private, public, commercial)
data collection on specific urban features, in order to verify their link with the degree of use private cars/public transit (i.a. urban walkability; accessibility; integration of the public transport network)
identify linkages between urban determinants of emissions and policies/measures
evaluate trends of urban emissions through cities’ updates of emissions inventories