Electric cars’ global-warming benefits are small. It is advertised as a zero-emissions car, but in reality it only shifts emissions to electricity production, with most coming from fossil fuels. As green venture capitalist Vinod Khosla likes to point out, “Electric cars are coal-powered cars.”

The most popular electric car, a Nissan Leaf, over a 90,000-mile lifetime will emit 31 metric tons of CO2, based on emissions from its production, its electricity consumption at average U.S. fuel mix and its ultimate scrapping. A comparable diesel Mercedes CDI A160 over a similar lifetime will emit 3 tons more across its production, diesel consumption and ultimate scrapping.

The results are similar for the top-line Tesla car, emitting about 44 tons, about 5 tons less than a similar Audi A7 Quattro.