Global Cities and Greenhouse Gas Emissions: U of T study of 10 cities ranks Toronto third after Denver, Los Angeles, and Barcelona lowest

Friday, December 4, 2009 11:00:00 AM

The world's population is now over 50% urban, and cities make an important contribution to national greenhouse gas (GHG) emissions.  Many cities are developing strategies to reduce their emissions.  Christopher Kennedy, Associate Professor in U of T's Department of Civil Engineering and graduate faculty member at the Centre for Environment, and colleagues ask how and why emissions differ between cities.  The study of ten global cities, recently published in the October 1 issue of Environmental Science and Technology1, shows how a balance of geophysical factors (climate, access to resources, and gateway status) and technical factors (power generation, urban design, and waste processing) determine the GHGs attributable to cities.  Within the overall trends, however, there are differences between cities with more or less public transit; while personal income also impacts heating and industrial fuel use.  By including upstream emissions from fuels, GHG emissions attributable to cities exceed those from direct end use by up to 25%.  With high population density, low heating requirements, and relatively clean electricity, Barcelona was found to have the lowest per capita emissions (4.2 t e CO2/cap.). Whereas Denver, having the highest per capita emissions for electricity, heating/industrial fuels, and ground transportation, was found to be the top emitter (21.5 t e CO2/cap.).  The next two highest cities were Los Angeles (13.0 t e CO2/cap.) and Toronto (11.6 t e CO2/cap.).

(This is an excerpt from the study available online at

C. Kennedy et al. 2009. Greenhouse Gas Emissions from Global Cities. Environmental Science Technology 43 (19): 7297-7302.