Earth Protect Blog

Few people are fooled by Nissan’s claim that the LEAF is a zero emissions vehicle.  Zero tailpipe emissions does not mean zero emissions.  “Electric vehicles just shift emissions from the tailpipe to the smokestack,” many critics claim.  Both of these claims oversimplify the issue and do not accurately reflect the potential impact of electric vehicles on greenhouse gas emissions.

In reality, electric vehicles shift emissions from the tailpipe to the smokestack, nuclear reactor, hydroelectric dam, wind farm and many other sources of electric power.  Ultimately, the impact of electric vehicles on greenhouse gas emissions is a function of the electric generation mix in a given region.  In the United States, the generation mix is nearly 50% coal and an additional 22% comes from natural gas and other fossil fuels (see image below, courtesy of MIT Electric Vehicle Team Blog).

With this generation mix, Samaras and Meisterling (2008) report that the average life cycle greenhouse gas intensity of electricity generation in the United States is 670 g CO2-eq/kWh.  At this level of greenhouse gas intensity, Samaras and Meisterling estimate that plug-in hybrids produce nearly 40% less lifecycle greenhouse gas emissions than conventional gasoline vehicles (see image below).  Even at the greenhouse gas intensity of coal, plug-in hybrids produce less lifecycle greenhouse gas emissions than conventional gasoline vehicles.

In comparison to conventional hybrids, plug-in hybrids produce slightly less lifecycle greenhouse gas emissions.  At the greenhouse gas intensity of coal, plug-in hybrids produce more lifecycle greenhouse gas emissions than conventional hybrids.  Therefore, in coal dependent states like West Virginia, buying a conventional hybrid as opposed to a plug-in hybrid will lead to a larger reduction in greenhouse gas emissions.  See the image below for a state-by-state summary of generation mixes (courtesy of MIT Electric Vehicle Team Blog).

Over the next few years, availability and purchases of electric vehicles will be concentrated in the northeast and west coast, where coal is a small fraction of the generation mix.  Most of these states have an average life cycle greenhouse gas intensity of electricity generation lower than natural gas.  Therefore, electric vehicles in the United States will lead to significant reductions in greenhouse gas emissions.  Electric vehicles are not zero emissions vehicles, but their potential impact on greenhouse gas emissions is significant enough to justify generous government rebates and all the attention they are receiving.