Yale School or the Environment

YSE study finds electric vehicles provide lower carbon emissions

A Yale School of the Environment study found the total indirect emissions from EVs pale in comparison to the indirect emissions from fossil fuel-powered vehicles.

January 12, 2022

New major spending packages are investing billions of dollars in electric vehicles (EVs) in the U.S. and analysts have raised concerns over how green the EV industry actually is, focusing particularly on indirect emissions caused within the supply chains of the vehicle components and the fuels used to power electricity that charges the vehicles.

 A Yale School of the Environment study published in Nature Communications found the total indirect emissions from EVs pale in comparison to the indirect emissions from fossil fuel-powered vehicles. The direct emissions from combusting fossil fuels at the tailpipe for conventional vehicles or at the power plant smokestack for electricity generation show EVs have a clear advantage emissions-wise over conventional vehicles.

“The surprising element was how much lower the emissions of electric vehicles were,” says postdoctoral associate Stephanie Weber. “The supply chain for combustion vehicles is just so dirty that EVs can’t surpass them, even when you factor in indirect emissions.”

Weber was part of the study led by Paul Wolfram ’21 PhD, a postdoc with the Joint Global Change Research Institute at the University of Maryland, YSE economics professor Ken Gillingham and former YSE faculty member Edgar Hertwich, who is now an industrial ecologist at the Norwegian University of Science and Technology. The research team combined concepts from energy economics and industrial ecology carbon pricing, life cycle assessment, and modeling energy systems to find if carbon emissions were still reduced when indirect emissions from the electric vehicle supply chain were factored in.

“A major concern about electric vehicles is that the supply chain, including the mining and processing of raw materials and the manufacturing of batteries, is far from clean,” says Gillingham. “So, if we priced the carbon embodied in these processes, the expectation is electric vehicles would be exorbitantly expensive. It turns out that’s not the case; if you level the playing field by also pricing the carbon in the fossil fuel vehicle supply chain, electric vehicle sales would actually increase.” 

The study also considered future technological change, such as decarbonization of the electricity supply, and found this strengthened the result that electric vehicles dominate when indirect supply chain emissions are accounted for. 

The research team gathered data using a National Energy Modeling System (NEMS) created by the Energy Information Administration, modeling the entire U.S. energy system using information from the current domestic energy system and a forecast of the future of the electric system. Wolfram completed a life cycle assessment that provided outputs of indirect emissions, which were then plugged into the NEMS model to see how a carbon tax on these indirect emissions would change the behavior of consumers and manufacturers. Weber assisted in modifying the NEMS code. 

According to Wolfram, the study shows that “the elephant in the room is the supply chain of fossil fuel-powered vehicles, not that of electric vehicles.” He notes that the faster we switch to electric vehicles, the better in countries with a sufficiently decarbonized electricity supply like the U.S. 

Gillingham, whose research focused extensively on alternative energy adoption in transportation, says this research provides a better understanding of how comprehensive carbon pricing which includes the full supply chain can shift consumers toward electric vehicles.