Cite as: Mohareb, E.A. & Kennedy, C.A., 2012. Greenhouse Gas Emission Scenario Modeling for Cities using the PURGE Model – a Case Study of the Greater Toronto Area. Journal of Industrial Ecology, 16(6), 875 – 888. 1 Greenhouse Gas Emission Scenario Modeling for Cities using the PURGE Model - a Case Study of the Greater Toronto Area Eugene A Mohareb & Christopher A Kennedy. Acknowledgements This study received financial support from people of Canada, through the Natural Sciences and Engineering Research Council. The authors appreciate the data provided by L. Bond, K.Crate, J. Humphries, L. Lewis, M. Nehme, R. Persaud, and J. Webster, as well as the comments provided by C. Andrews, D. Harvey, H. MacLean, and K. Pressnail. Introduction Cities face an ongoing challenge to decouple their growth from their resource consumption (Kennedy et al, 2007). One consequence of this is that greenhouse gas (GHG) emissions from cities will continue to rise unless the technology stock of cities no longer relies on fossil fuels to provide energy services. Technological solutions are routinely suggested as a means for reducing the emissions of GHGs contributing to climate change (e.g., Pacala and Socolow, 2004). These technological measures include fuel switching (i.e. coal to natural gas), adoption of renewable energy sources, the pursuit of carbon sequestration and the transition to higher efficiency conversion technologies. The gaps that these technologies must bridge are expansive; Meinshausen et al (2009) suggest that a peak CO 2 e concentration of 450 ppm would likely limit warming to below 2 o C, avoiding some of the most severe consequences of climate change. The IPCC suggests that to achieve this concentration, Annex I nations need to reduce their GHG emissions by 80-95% from 1990 levels by 2050 (Box 13.7; IPCC, 2007). Hence, there is value in modeling the impact of technological changes from now until 2050. This article describes an urban-scale model where temporal considerations of GHG emission reductions associated with transitions to low-carbon technologies can be examined. The Pathways to Urban Reductions in Greenhouse gas Emissions (or PURGE) model focuses on the principal sources of GHG emissions attributable to cities: buildings, transportation, and waste. The rate of building stock change, as well as the adoption of and decisions for retrofitting, are applied to the model for different eras of construction. The adoption of vehicles powered through alternate propulsion systems (i.e. those with electric motors) is also examined, reducing reliance on petroleum fuels. Total annual electricity demand is likely to increase due to the anticipated reliance on