Today we review a more sophisticated estimate of the ecological footprint of a city using a 3rd generation urban metabolic model called UM-LCA for short. The model is applied to five cities with different characteristics: Cape Town, Toronto, Beijing, London and Hong Kong and the resulting estimates reveal large differences in per capita contributions to global warming and energy flows, showing once again the destructive outcomes from sprawled cities and private vehicle use such as Toronto and of the relative emissions from residences and industry.
“The contribution of cities to a number of global environmental pressures such as climate change, water stress, biodiversity loss and resource scarcity is recognized to be strong…These pressures will likely increase vastly.. the percentage of urban dwellers worldwide is predicted to swell from 50% currently to 70% of total population by 2050”
“UM [urban metabolism] refers to a broad range of quantitative methods that attempt to conceptualize urban areas as organisms, requiring goods and energy to maintain functionality and support growth, while emitting waste as a byproduct”
"For all of the cities except Beijing embedded mass flows accounted for more than 60% of the total mass flows resulting from the cities’ metabolic activities,”
“Energy consumption through the cities showed a similar trend, with the embedded energy flows contributing between 48% (Toronto) and 76% (Hong Kong) of the cities’ total life cycle energy requirements.”
“The per capita GWP [global warming potential] for the cities, according to the UM–LCA model, are: 10.2 tons for Hong Kong, 11.2 tons for Cape Town, 12.2 tons for London, 17.2 tons for Beijing and 18.0 tons for Toronto”
“For the wealthier cities, Toronto as an example, the largest contributing factors to the GWP are transport (27%) and building energy (24%), with waste disposal also playing a large role (21%) due to the city’s composting activities that generate methane… GWP from transport stems primarily from the high usage rates of private automobiles in the city”
“Wealthier case cities tend to mitigate air pollution issues through the use of cleaner technologies in energy generation, consistent with the theory that local environmental pressures are inversely related to the wealth of the potentially affected population”
“The conceptual UM–LCA model has the potential to provide an improved assessment tool for urban environmental loading beyond earlier UM methods through inclusion of the environmental pressures embedded in the goods that cities consume and by offering a clear set of communicative indicators.”
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