This is interesting: WorldChanging: How the West was warmed.
The conclusion seems to be that per capita people in cities emit less CO2 than less populated areas.
Of course it can be very misleading to focus only on direct emissions. When we consume things then there are CO2 emissions throughout the items lifecycle and for people in the cities much of this will be elsewhere (eg electricity generation, production of cars, transportation of all we consume, …).
Still worth doing and reflecting on.