American Electric Vehicles
Courtesy of Carnegie Mellon University
What time of day the recharging electrons flow form a wall plug into an electric car’s batteries also matters in this calculation. Nighttime is often when the wind blows but it is also when utilities like to run only their coal-fired power plants. A recent study found that an electric car charged by utilities at night in the regional grid that stretches across Ohio, Delaware, Pennsylvania and Virginia creates more greenhouse gas pollution than if owners plugged in their vehicles at random times throughout the daytime, when the utility fuel mixes are more varied.
The same argument applies worldwide. Driving an electric car in China, where coal is by far the largest power plant fuel, is a catastrophe for climate change. And if the coal plant lacks pollution controls—or fails to turn them on—it can amplify the extent of smog, acid rain, lung-damaging microscopic soot and other ills that arise from burning fossil fuels. The same is true in other major coal-burning countries, such as Australia, India and South Africa.
The good news: the U.S. is making a tectonic shift from burning coal to produce the majority of its electricity to using cleaner natural gas. The changeover produces less CO2, making electric cars cleaner across the country, roughly equivalent to a hybrid. On the other hand, the primary constituent of natural gas—methane—is itself a potent greenhouse gas. If methane leaks from the wells where it is produced, the pipelines that transport it or the power plants that burn it, the climate doesn't necessarily benefit.
In short, electric cars are only as good as the electricity that charges them. (A fuel’s source also matters for conventional cars; gasoline derived from tar sands is more polluting than that from most other petroleum resources, for example.) In the absence of clean electricity, hybrid cars that can travel 50 or more miles on a gallon of gasoline produce the least emissions.
Electric cars still constitute less than 1 percent of U.S. car sales, and even less of the global fleet that is now approaching two billion vehicles. So their environmental benefit—dubious for now, until more power plants get off coal—is not very worrisome. The current shift back to SUVs that guzzle much more petroleum than other cars, prompted by low gasoline prices, is a more worrisome sign for future climate change. Perhaps by the time electric cars are ubiquitous, pollution from generating electricity will be zero.