Electric cars may end up being worse for the climate and for human health than gasoline-fueled vehicles, depending on whether coal or some other source is being used for electricity generation, according to a study conducted by researchers from the University of Minnesota and published in the Proceedings of the National Academy of Sciences in December 2014.
Ethanol-fueled vehicles are also worse than gasoline-powered ones, the study found.
“A lot of the technologies that we think of as being clean … are not better than gasoline,” co-author Julian Marshall said.
“Unfortunately, when a wire is connected to an electric vehicle at one end and a coal-fired power plant at the other end, the environmental consequences are worse than driving a normal gasoline-powered car,” said Ken Caldeira of the Carnegie Institution for Science, who was not involved in the study.
Coal is primary U.S. electricity source
Studies conducted by Climate Central in 2012 and 2013 had showed that the greenhouse gas emissions of vehicles running off electricity sourced from coal were worse than those of gasoline-powered vehicles. The new study confirmed those prior findings and also expanded them to encompass health impacts of various energy sources.
The researchers examined 10 different ways to power automobiles, including gasoline, diesel, liquid biofuels, compressed natural gas and electricity from a variety of sources, both conventional and alternative. They then calculated all the air pollution emitted from the process of producing the fuels (or batteries or electricity), as well as the pollution emitted during the vehicle’s operation. They then estimated the health and climate effects of these emissions.
Researcher Jason Hill emphasized that just looking at the emissions from a vehicle’s tailpipe can dramatically underestimate a fuel source’s health and environmental impact. For example, ethanol fuels are also responsible for air pollution released from the vehicles used to grow the corn, from the soil following the application of fertilizer, and from the process of fermenting and distilling the corn into ethanol.
When it come to electric vehicles, the source of the electricity is the key question. According to the U.S. Department of Energy, 39 percent of the country’s electricity comes from coal, 27 percent from natural gas, about 20 percent from nuclear power, 7 percent from dams or water turbines, and 6 percent from all other sources.
Coal, ethanol more lethal than gasoline
The researchers found that electric cars run from coal actually kill 360 percent more people than cars run from gasoline, due to increased soot and smog emissions. They also emit significantly more carbon dioxide, a greenhouse gas.
In contrast, natural gas-powered electric cars would only kill half as many people as gasoline-powered cars. Electric cars powered from wind or water energy would cause only 25 percent as many air-pollution-related deaths. Hybrid and diesel engines were also lower-impact than gasoline engines.
Ethanol, in contrast, causes 80 percent more air pollution-related deaths than gasoline, and also emits more greenhouse gases.
“If we’re using ethanol for environmental benefits, for air quality and climate change, we’re going down the wrong path,” Hill said.
“Any honest accounting of greenhouse gas mitigation strategies must… consider the possibility of unintended consequences,” said Timothy Johnson of Duke University, who was not involved in the study.
Johnson noted that other impacts of different energy sources might include local environmental effects of producing or using the fuels, such as increased air pollution from truck traffic to ethanol refineries.
“While these considerations go beyond the paper’s focus on air quality, the study reminds us that we need to widen our analytical boundaries if we are going to address greenhouse gas emissions sustainably,” Johnson said.
Another impact might be destruction of water supplies due to mining for raw materials for solar panels, batteries or other alternative energy sources.