Cars are not the problem, there is no one thing that is the problem. Simply being alive and doing things uses energy, there is no way around that.
And BTW if you do the math a bicyclist (in the US, eating a typical US diet) emits more CO2 per mile than a small car. Assumptions: The bicyclist is riding in addition to any exercise, the riding is not exercise, and the bicyclist eats normal food. A bicyclist who prefers organic, or local, would definitely emit more (both of those emit more CO2 in the growing than regular food).
It's a surprising result, I know. But it's because humans are not very efficient in turning food energy into miles, and cars are reasonably efficient. It doesn't help that growing food takes a lot of energy, especially if you force yourself to only eat local, if you do that energy really goes up.