Carbon In, Carbon Out

This morning the Union of Concerned Scientists, an environmental advocacy group, will release a report that compares the carbon footprints of electrically powered cars with gasoline models. On this map, the numbers following the city names represent, as a miles-per-gallon equivalent, the amount of greenhouse gases generated in charging the battery of an electric Nissan Leaf in that city.
The darkest regions on the map are served by utilities burning a high percentage of coal to generate power; in those regions, charging an electric car sends as much carbon dioxide into the atmosphere as driving a car rated at 31 to 40 m.p.g., about the same as a current compact model. In the lightest areas of the map the electricity is generated by cleaner fuels, so the equivalent miles per gallon is higher than the best of today’s hybrids.
Cities marked with an asterisk are served by utilities that are situated in a different electrical grid region. Readers in those cities can use the ZIP code lookup tool on the Energy Department’s Alternative and Advance Vehicles Web page to determine the fuels used to generate local power

http://www.nytimes.com/interactive/2012/04/13/automobiles/Sorting-Out-the-Power-Grid.html