What does it take to produce a low-carbon city? First, it should be compact. The average resident of Barcelona emits about a tonne a year of carbon dioxide equivalent (CO2e), while a New Yorker emits about one and a half and someone from Denver emits well over six. Torontonians emit about 4 tonnes of CO2e per year, from ground transport. This suggests that high-density urban planning might be a realistic component in climate change mitigation plans.
Secondly, it helps to be located in a temperate climate and to rely on low-carbon forms of electricity, such as hydro and nuclear. The worst thing to be is spread out, located in a very cold or very hot climate, and powered by coal. Phasing out coal globally should probably be our #1 climate priority.
Of course, tomorrow’s low-carbon cities will need to do dramatically better. Those annual ground transportation emissions are higher than the acceptable level for total emissions per capita by 2050.