The study was performed by researchers at the University of Toronto, and compared ten global metropolises.
"Dr Christopher 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."