An all-electric Chevrolet Bolt, for instance, can be expected to produce 189 grams of carbon dioxide for every mile driven over its lifetime, on average…

On the other hand, if the Bolt is charged up on a coal-heavy grid, such as those currently found in the Midwest, it can actually be a bit worse for the climate than a modern hybrid car like the Toyota Prius, which runs on gasoline but uses a battery to bolster its mileage. (The coal-powered Bolt would still beat the Camry and the F-150, however.)

“Coal tends to be the critical factor,” said Jeremy Michalek, a professor of engineering at Carnegie Mellon University. “If you’ve got electric cars in Pittsburgh that are being plugged in at night and leading nearby coal plants to burn more coal to charge them, then the climate benefits won’t be as great, and you can even get more air pollution.”
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