Newswise — One motivation for driving an electric car (or a plug-in hybrid in electric mode) is that it doesn't spew climate-warming carbon dioxide from its tailpipe. But for most people, such a vehicle would still cause the release of considerable CO2--at the power plant that generates the electricity used to recharge. To assess the green credentials of an electric car or PHEV then, you have to examine the carbon intensity of your local electric grid.

On average in the United States, driving a car that runs on grid-produced electricity generates slightly less carbon dioxide than driving a conventional hybrid (or similarly economical combustion-only vehicle). But in some states, where the grid creates a lot more CO2 per kilowatt than the national average, driving an electric car is not the greenest choice. The same holds for most places in China, for example, where the electric grid is powered chiefly by coal-fired power plants. So caution is warranted: Perhaps China should not embrace electric vehicles for the time being and only do so after it has cleaned up its domestic power grid.