Are you really doing the environment a favor by buying and driving an electric car?
The answer may depend on where in the country you live.
New research indicates the impact of electric cars on the environment is much more nuanced than many people realize.
Dartmouth College research Erin Mansur says his analysis shows that electric cars cause more environmental damage than gasoline-powered cars in some areas of the country.
For example, electric cars in Michigan mainly get their power from coal-burning power plants.
Running the plants more in order to charge electric cars puts extra pollutants into the air. So Mansur says in the eastern U.S. and Midwest, "under today's grid, there's more of an environmental footprint from an electric Ford Focus than a gasoline Ford Focus."
In Michigan, Mansur says an electric Focus causes about as much damage to the environment as a new gasoline-powered pickup truck.
In California, however, Mansur says an electric Focus causes significantly less environmental damage than a gasoline-powered Ford Focus.
That's mainly because California gets most of its electricity from cleaner natural gas power plants.
Mansur says another thing people need to realize is that an electric car tends to export its environmental damage to other states.
A car that burns gasoline emits most of its pollution, like nitrogen oxides, into the local environment.
But electric cars plug into a multi-state grid.
"You're getting some of that electricity locally, but some of it is coming from longer distances away," says Mansur.
So an electric car in Indiana might be pulling energy from a coal-burning power plant in Michigan, for example, but Michigan gets the pollution.
Mansur says the current one-size-fits-all $7,500 federal subsidy for buying an electric car may need to be modified to account for this effect, since it may give some states an incentive to export the environmental consequences of vehicles to other states.
Mansur acknowledges the electric grid is slowly becoming cleaner, as coal-burning power plants are shut down. So over time, electric vehicles will have a greater positive effect on the environment.