A new working paper by a team of economists has recently been characterized as showing that electric vehicles (EVs) are worse than gasoline vehicles (for example: “Electric Cars: Not So Environmentally Friendly After All?”). On the one hand, this study reiterates what we and others have said: plug-in electric vehicles have greater air quality and global warming emissions benefits when they are charged using sources of electricity cleaner than coal, like natural gas or renewables like wind and solar. Unfortunately, however, the authors’ conclusions that EVs are worse than gasoline vehicles are based on questionable assumptions about electricity sources, air pollution sources, and vehicle characteristics that bias their overall results against electric vehicles.
Source: Flickr
Here are a couple of the shortcomings:
- Pollution from producing gasoline is not accounted for
An important missing piece in the analysis are the “upstream” emissions. These are the global warming emissions and air pollution generated during the extraction and processing of fuels. Both electricity and gasoline have upstream emissions (like coal mining, crude oil production, gasoline refining, and trucking of fuel to the gas station), and they can be significant. For gasoline vehicles, 22% of global warming pollution, 44% of particulate matter, 59% of nitrous oxides, and almost all of the sulfur oxides are produced in these upstream processes, so ignoring them gives an incomplete picture. The location of the upstream emissions would also change the results of this study, as not all of the gasoline emissions would occur in the counties where the vehicles are driven.
- Gasoline vehicles are driven in cold weather too
There is also a questionable assumption about vehicle performance. The authors argue that electric vehicles are less efficient in low temperatures and therefore reduce the electric vehicle efficiency in regions with colder climates. This is a correct assumption, but they neglect to perform a similar correction for gasoline and hybrid vehicle performance. Since all vehicles are less efficient at colder temperatures, applying this penalty only to electric vehicles biases the results to favor gasoline vehicles.
- The electricity grid is changing
Finally, the analysis is based on historical emissions from fossil fuel powered electricity generation. This ignores both the on-going shift away from coal-powered electricity and the current policies that encourage and require less coal and more renewable power. For example, the paper does not consider the caps on both air pollution and global warming emissions in several regions. In the future we can expect to see both cleaner electric power and also policies and technologies that link electric vehicle charging to renewable energy availability.
So what would changing these assumptions do to the results? We can’t know exactly, but the researchers did examine the sensitivity of their results to some of these assumptions.
In the baseline case, the average environmental benefit is calculated to be equal to -0.46 cents/miles (that, is gasoline cars are cleaner). However, removing the temperature penalty from electric vehicles increases their benefits by 0.14 cents/mile. We can’t tell what the impact of considering both electricity and gasoline upstream emissions is, but they do calculate that doubling the gasoline emissions would change the results so that gasoline vehicles and EVs would be approximately equal. Most importantly, the paper also examines a future power scenario where both somewhat cleaner power is available and more efficient gasoline vehicles are the norm. In this case, electric vehicles have a net benefit of 0.64 cents/mile. Taking into account upstream emissions, vehicle performance, and future cleaner power would likely show a benefit across much more of the country. It also highlights the importance of moving forward with both electric vehicles and renewable electricity, two technologies that are available and expanding in the United States.
Outside of the technical assumptions, I also have to question the comparison of the single vehicle environmental benefit to the federal and state purchase incentives. As the authors note, “The subsidies reflect beliefs that electric vehicles generate a range of benefits including: decreased reliance on imported oil, insulation from oil price shocks, and a reduction in environmental impacts.” Yet, only this last benefit is assessed in this study, so it’s unclear why the total subsidy is used as the comparison.
Moreover, the current electric vehicle incentives are not just designed to sell cars today. The more important effect is to spur research, build demand for electric vehicle charging infrastructure, and increase awareness of petroleum-free transportation options.
We need both clean electricity AND clean vehicles and that’s why we advocate for both. Currently, the average electric vehicle results in lower global warming emissions when compared to the average new gasoline car, no matter where in U.S. it’s recharged. In many places EVs are better than the most efficient gasoline car. And as the production of electricity becomes cleaner, so will electric cars.
Update: Eric Jaffe at CityLab just wrote an excellent piece covering some of these same issues. Find it here.