Electric Cars Can Make Cities Cooler

Electric vehicles have gotten a lot of support because they have the potential to reduce air pollution and greenhouse gas emissions. Now it seems these cars may have another benefit—cooler cities.

A conventional gasoline engine is incredibly inefficient. Most of the energy produced by the tiny explosions inside is actually lost as heat. The engine that runs an electric car, by contrast, is much more efficient and loses far less energy to heat. The difference is enough that if all the cars in Beijing were replaced with electric versions, the city would be almost 2 degrees Fahrenheit cooler in summer, researchers conclude today in Scientific Reports.

This is especially important in metropolitan regions that experience the urban heat island effect, when cities are hotter than the surrounding countryside because all those buildings and concrete interfere with how efficiently the region can release heat into the air. “The stronger the urban heat island effect, the greater the benefits,” says study leader Canbing Li of Hunan University and Michigan State University.

Li and his colleagues investigated how switching to electric vehicles would affect the urban heat island of Beijing. In that city, which has experienced temperatures as high as 122 degrees in past summers, half of the excess heat comes from vehicles and building air conditioners. In 2012 in Beijing, an electric vehicle emitted on average only 19.8 percent as much heat as a conventional vehicle, the researchers found. Some heat would still be generated by the power plants that produce energy for electric cars, though that didn’t matter so much since these sites are usually far from city centers. But there would also be a feedback when it came to air conditioning—lower heat emissions from vehicles would reduce city temperatures, so people wouldn’t have to use so much AC.

Overall, replacing conventional gas-guzzlers with electric cars would save some 14.4 million kilowatts of energy each day and reduce carbon dioxide emissions by nearly 12,000 tons daily, the researchers calculate. And instead of Beijing being 5.4 degrees warmer than the surrounding countryside, it would be only 3.7 degrees hotter. Li says he expects that other cities would see similar benefits.

That doesn’t mean that everyone should run out and buy a Tesla. Even Li doesn’t intend to buy an electric vehicle until his car reaches the end of its service life. And he and his colleagues note that there is an increasingly heated debate on whether the replacement of conventional vehicles by electric ones should be delayed or accelerated, because the manufacturing processes for new technologies are more costly and cause more pollution than those for conventional cars.

In addition, the benefits for battling climate change and reducing pollution aren’t all that clear at this time. There are challenges to switching from engines and furnaces that burn fossil fuels to ones that run on electricity, such as the environmental impacts of battery disposal and costs, University of Toronto civil engineer Christopher Kennedy noted in a recent commentary in Nature. The root source of energy for a vehicle’s batteries makes a huge difference. A study published in Environmental Science & Technology in 2011, for instance, concluded that electric cars in China actually generated more harmful air pollution than gasoline cars because the country's electricity came largely from coal-fired power plants.

Kennedy notes that greenhouse gas emissions also “are only reduced under electrification strategies if the displaced fossil fuels are replaced by electricity of suitably low carbon intensity.” In other words, the electric car scheme only works for lowering pollution and preventing climate change if the vehicles draw their energy from renewable sources like wind and solar.

The reduction in summertime city temperatures, though, would be a nice benefit.

Sarah Zielinski | | READ MORE

Sarah Zielinski is an award-winning science writer and editor. She is a contributing writer in science for Smithsonian.com and blogs at Wild Things, which appears on Science News.