Using the city of Toronto as a case study, this article examines impacts of energy stocks and flexible demand in the urban metabolism on the resilience of the city, including discussion of directions for further study of the resiliency of the urban metabolism. An important element developed is the nominal residence time of the energy stocks. This value defines how long an energy stock lasts under typical patterns of energy use. The findings suggest that the residence times of many sources of energy overcome vulnerability when energy supply shocks last on the order of hours or a few days, but that the measure is limited to assessing only certain types of commonly used energy sources in aggregate terms. Discussion is included on the uncertainty of this measure and on the metabolic and resiliency implications of new technologies intended to reduce energy use and improve sustainability of cities and the use of the urban metabolism as a means of comparison. The methodology employed highlights how waste energy could be used to increase the resiliency of the city's water supply, but also how the study of the urban metabolism would benefit from a more disaggregate form in the study of sustainable and resilient cities.

SummaryThis forum article explores thermodynamic understanding of the growth of cities, including theoretical foundations, observations, and analysis. The general theory of nonequilibrium thermodynamics is reviewed, recognizing differences in interpretation between Prigogine and Schneider and Kay as well as discussing the hypothesis of maximum entropy production. Calculations of exergy gradients in a few cities and settlements, along with measures of anthropogenic heat loss in further cities, support the notion that cities are dissipative structures. The observation that primary energy use per capita increases in Singapore and Hong Kong as they grow is further evidence to support the thermodynamic understanding of the growth of cities, indicative of an increasing rate of entropy production. At the global scale, the strong linear relationship between global urban population and total global energy use, and the distribution of city sizes according to Zipf's law, can be understood as emergent results based on thermodynamics. Parallel results might be derived from models that represent underlying microscale processes, several of which are reviewed. Issues for future research include: development of nonequilibrium thermodynamic models specific to city growth; further study of exergy flows of cities with consistent methodology, including attention to solar energy exchanges in cities; and further exploration of links between thermodynamic and economic models of urban growth.

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Summary The seasonal and hourly variation of electricity grid emissions and building operational energy use are generally not accounted for in carbon footprint analyses of buildings. This work presents a technique for and results of such an analysis and quantifies the errors that can be encountered when these variations are not appropriately addressed. The study consists of an hour‐by‐hour analysis of the energy used by four different variations of a five‐story condominium building, with a gross floor area of approximately 9,290 square meters (m2), planned for construction in Markham, Ontario, Canada. The results of the case studied indicate that failure to account for variation can, for example, cause a 4% error in the carbon footprint of a building where ground source heat pumps are used and a 6% and 8% error in accounting for the carbon savings of wind and photovoltaic systems, respectively. After the building envelope was enhanced and sources of alternative energy were incorporated, the embodied greenhouse gas (GHG) emissions were more than 50% of the building's operational emissions. This work illustrates the importance of short‐time‐scale GHG analysis for buildings.