A number of friends of ours have electric cars, and hoo boy are they fun. (Got to drive a Tesla recently and holy smokes does it have some get-up-and-go.) A reader asked me recently how much an electric car–over lifetime–reduces CO2 output versus a conventional car. They wondered whether charging a car with a predominantly hydrocarbon-based energy grid actually helped the environment. It could be a major environmentalist’s dilemma.