Battery-electric cars produce no direct carbon emissions from driving, but those are not the only potential source of emissions related to these vehicles.
The lifetime carbon emissions of electric cars seem to be the question that launches a thousand studies.
Critics of electric cars have suggested that emissions related to their construction are higher than those of gasoline cars, and thus can cancel out emissions saved by actually driving them.
Now, yet another study has refuted that notion.
Electric cars do indeed have higher manufacturing-related emissions than gasoline cars, but lower overall lifetime emissions, according to a Union of Concerned Scientists (UCS) study issued last November.
Researchers compared an 84-mile Nissan Leaf to a comparably-sized gasoline car averaging 29 mpg, and compared a 265-mile Tesla Model S to a similarly-sized gasoline car getting 21 mpg.
Manufacturing-related emissions were found to be 15 percent higher for the Leaf, and 68 percent higher for the Model S.
The largest single source of emissions in this area was battery manufacturing, which accounted for 24 percent of the Leaf's total, and 36 percent of the Tesla's total.
But the electric car's "cradle-to-grave" carbon emissions remained much lower than those of gasoline cars.
The Leaf had 51 percent lower emissions over an assumed lifetime of 179,000 miles than a comparable gasoline car, while the Model S had 51 percent lower emissions.
That's because the battery-powered cars consumed far less energy while being driven--a benefit that becomes apparent almost immediately.
The Leaf's extra manufacturing-related emissions were offset within 4,900 miles of driving, or about six months of ownership, assuming sales-weighted electricity emissions based on where electric cars are sold today.
The Tesla's manufacturing-related emissions could be offset within 19,000 miles of driving, or about 16 months of ownership.
Both figures could increase or decrease, depending on whether the cars are charged using clean renewable energy, or higher-carbon sources for their electricity.
That's also true of manufacturing; the UCS said manufacturing-related emissions could vary by up to 30 percent, depending on the sources of electricity used to power factories.
The next area for inquiry would appear to be how plug-in hybrids with various ranges and drive cycles compare to pure battery-electric vehicles.
Plug-in hybrids have smaller battery packs, which would lower the main source of manufacturing-related emissions for electric cars.
And they can still drive on electric power some or most of the time--perhaps enough to lower driving-related emissions and close the gap with all-electric cars.
That's another study for another day, it seems.
This article first appeared at GreenCarReports.