Urban Metabolism

A great concept that can be used by Indian cities to compare their carbon footprint.

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Sep 28th 2009  From

Cities can learn from comparing their carbon footprints

HOW and why do greenhouse-gas emissions differ between cities? Since more than half of the world’s people now live in such metropolitan areas, that is an important question. If the worst could copy the habits of the best, climate change might be slowed significantly.

To address this question a team of researchers led by Christopher Kennedy of the University of Toronto has compared the emissions of ten conurbations. Four were in North America (Denver City and County, Los Angeles County, New York City and the Greater Toronto Area). Four were in Europe (Barcelona City, the Canton of Geneva, the Greater London Authority area and the Greater Prague Region). The other two were in Asia (Bangkok) and Africa (Cape Town).



Dr Kennedy and his colleagues tried to quantify the contributions of heating, transport and waste disposal, among other things, to the emission of greenhouse gases in each of these cities, and to calculate the emissions per person that resulted. They also included in their calculations some emissions that took place outside the city limits, such as those associated with the production of fuel that was consumed in the cities in question.

The results, which will be published in the October 1st issue of Environmental Science and Technology, showed that the total emissions of the ten chosen cities varied considerably, ranging from 4.1 tonnes of carbon dioxide per person in Barcelona to 21.5 tonnes in Denver. Other low emitters included Geneva and Prague; Los Angeles, Cape Town and Toronto were among the high emitters. The rest fell in between.

Given this variation, Dr Kennedy recommends that city mandarins compare building codes and other policies, to identify environmentally friendly practices. Of course Denver, with its snowy winters and warm but wet summers, cannot learn much from Barcelona, with its Mediterranean climate, because they are so dissimilar. But it might learn from Toronto, which emits 11.6 tonnes of carbon dioxide per person and is closer to Denver in climate and population density.

Meanwhile a separate piece of research published on September 28th in Environment and Urbanization concludes that, in contrast to a study your correspondent reported recently (see “Fewer feet, smaller footprint” September 21st), population growth itself does not drive the growth of greenhouse-gas emissions. David Satterthwaite of the International Institute for Environment and Development, a British think-tank, reckons that it is, rather, the growth in the number of consumers and in their levels of consumption that drives emissions growth. An obvious point, perhaps, but as advisers preparing to meet at the United Nations Climate Change Conference in Copenhagen can attest, even getting people to acknowledge the obvious can be an uphill struggle.

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