To paraphrase Leo Tolstoy: Every polluting city pollutes in its own way. Yet until recently, just how and whence Los Angeles, Bangkok, and eight other global cities exhaled their climatec-hanging vapors was a topic shrouded in mystery. Now, a 10- city comparison of greenhouse gas emissions per capita is showing metropolises “exactly where their emissions are coming from,” says Christopher Kennedy, an associate professor of civil engineering at the University of Toronto and the study’s lead author. The research “could also help cities learn from each other,” he adds. Aside from the usual finding that North American cities are the heaviest breathers, Kennedy and his team reveal that each urban area has a distinct emissions profi e. (See these profiles on the graph below.) Mile-high Denver and temperate Toronto burn lots of fossil fuels to generate electricity for their businesses and industries, as well as to stay warm during their frostier months. At the same time, hydropower keeps Geneva’s electricity- related emissions low. Yet cold winters drive up Geneva’s heating oil-induced effluvia, as they do for New York and Prague. But New York spares the air many of its transportation-related fumes with high population density and good public transit, as…