The cool car: electric vehicles show possible benefit to combat global warming

Figure courtesy of geograph.org.uk

Figure courtesy of geograph.org.uk

Electric vehicles have been touted as a revolution waiting to happen to our transportation grid, just as soon as we can make a battery that provides long-range travel between charging stops.  They are also sold as a way to avoid pollution and curb global warming since they don’t emit carbon dioxide from gasoline combustion.  But their pollution-free label isn’t entirely true.  Electric cars cost more to make, and actually pollute more than normal cars during manufacturing.  This begs the question of whether we should wait to push them to market until we have more environmentally friendly ways of making them.

A new article from Scientific Reports, however, suggests we should still try to replace current cars with electric varieties due to hidden benefits of electric vehicles that haven’t been talked about before.  In short, they’re cooler!  This ends up providing a net effect of reducing greenhouse gas emissions from air conditioners that are used to counteract the heat increase from conventional cars.  A collaborative effort between researchers at Michigan State University and in China, the report is extremely short with some simple math to explain the argument, so I recommend giving it a read!

The argument revolves around a phenomenon known as the urban heat island effect.  In cities and urban environments, black, dry roads and buildings have replaced normal vegetation, which leads to sunlight increasing the temperature of these areas much more easily (I think mainly due to lack of water in these regions, which can take in substantially more energy without increasing its temperature).  In addition, the huge number of cars congested in urban areas release heat during gasoline combustion, and air conditioners also release heat during operation.  All these factors leading to 5-7 F (1-3 C) increase in temperatures in urban regions compared to the surrounding rural parts, as shown below:

Figure courtesy of wikipedia.org

Figure courtesy of wikipedia.org

Here’s where electric vehicles can help.  Electric motors are intrinsically more efficient than their internal combustion counterparts, and therefore the energy they release over the same mileage driven is much less.  According to calculations in the report, this leads to electric vehicles emitting only one fifth the heat energy of conventional vehicles.  This means less heat emitted in urban environments, which means air conditioners need to do less work to reduce temperature.  This in turn would require less electricity from fossil fuel plants that are required to run the air conditioners, and thus less CO2 emissions emitted into the atmosphere that lead to global warming.  This general pattern of relationships is shown in the diagram below, where HII is a measure of the heat island effect commonly used in the literature and measured in degrees C:

Figure courtesy of [1]

Figure courtesy of [1]

This is the essential argument worked out mathematically in the paper, so I’ll leave it to you to check out the numbers if you’re interested.  The analysis used Beijing as an example city for the calculations and required the authors to combine data from many other research articles, such as the total electricity consumption in Beijing, heat release from power plants per unit energy created, etc.  They seem accurate, if maybe a bit too general and hand-wavy.  There are many other factors that could affect the urban heat island effect, such as aerosol pollution in the atmosphere and how different surfaces absorb more or less heat.  The authors acknowledge these other variables but don’t include them in any analysis.

I think the take-home message is still important: there are many interrelated factors that will be affected by shifts in the transportation economy from conventional, gasoline-powered cars to electric ones.  It is crucial to assess environmental impacts across the lifespan of any consumer good, from manufacturing to maintenance to removal, and it is this type of analysis that shows that electric vehicles do pollute during manufacturing.  However, downstream effects of their addition to the economy as shown here indicate the hidden benefits.  This is mainly because of more efficient energy generation in electric vehicles that leads to reduced heat release.  On the scale of cities with millions of potential drivers, the benefits from this more efficient engine can add up to take sizable chunks out of our greenhouse gas emissions.

References

1)

Li C, Cao Y, Zhang M, Wang J, Liu J, Shi H, & Geng Y (2015). Hidden benefits of electric vehicles for addressing climate change. Scientific reports, 5 PMID: 25790439

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