Electric cars have no tailpipe emissions when running.

But unless they're charged entirely on renewable energy—still statistically unlikely today—there are emissions associated with generating the electricity used to charge their batteries.

For several years now, rigorous "wells-to-wheels" analyses of the carbon-dioxide emissions associated with electric-car use have shown it's far lower than that of the average vehicle sold today.

DON'T MISS: Different map shows electric cars are cleaner

The Union of Concerned Scientists released an updated version of its MPG-equivalencies map last week, showing what fuel efficiency would be necessary in a gasoline car to equal the carbon footprint of an electric car on different U.S. regional electric grids.

The group explains in detail the methodological changes it made to its latest estimates, but the crucial point remains the same: the grid mix varies considerably from state to state and region to region.

The West Coast and the Northeast have the lowest-carbon grids, meaning gasoline cars would have to get 70 mpg or better to be as clean as electric cars in those regions.

2017 Chevrolet Bolt EV

2017 Chevrolet Bolt EV

Other grids have lower equivalencies, but only one—in the Rocky Mountains—is below 40 mpg, using the most recent grid data (from 2014) and a sales-weighted average of 2016 electric-car sales. 

Six regional grids fall between 41 mpg and 50 mpg, and everywhere else is higher than 50 mpg—with the best, in New York state above New York City, at a whopping 160 mpg.

In other words, to emit as little carbon per mile as an electric car charged on the New York state grid, a gasoline car would have to be rated at 160 miles per gallon. Which will never happen without a plug.

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The data also lets us calculate the percentage of U.S. residents who live in areas where electric cars will always be better than non-electrified gasoline cars (which excludes hybrids).

For 2017, the most fuel-efficient non-hybrid vehicle sold in the U.S. is the Mitsubishi Mirage minicar equipped with a continuously variable transmission, at a combined 39 mpg.

The UCS calculates that only 3 percent of U.S. residents live in a place where that Mirage would be better on carbon than an electric car. (Not to mention that many buyers won't even consider a car that small and slow.)

2016 Toyota Prius Two Eco

2016 Toyota Prius Two Eco

2016 Toyota Prius Two Eco

2016 Toyota Prius Two Eco

2016 Toyota Prius Two Eco

2016 Toyota Prius Two Eco

In other words, 97 percent of U.S. buyers will emit less carbon if they drive an electric car instead of any non-hybrid gasoline car.

It's more complicated when you include hybrids. The UCS chose 50 mpg or better as its cutoff because Toyota Prius models from 2010 through 2016 were rated at 50 mpg combined.

For 2017, the two highest-mileage hybrids on sale (without a plug) are the Toyota Prius Two Eco at 56 mpg combined and this year's champ, the Hyundai Ioniq Blue at 58 mpg combined.

CHECK OUT: In Just One Year, Electric Cars Have Gotten Cleaner: How'd They Do That? (Dec 2014)

MPG equivalencies run between 40 mpg and 50 mpg for another 27 percent of U.S. residents, and three regional grids in Texas and the southeast fall between 50 and 60 mpg.

For buyers in those regions, driving a hybrid—today—will be slightly better on total wells-to-wheels carbon emissions than driving an electric car.

However, even for them, that number won't stay static for long. Across the country, coal plants continue to be retired in favor of natural-gas generation, and renewable energy usage grows every year.

BMW i3 and Volkswagen e-Golf electric cars using Combined Charging System (CCS) DC fast charging

BMW i3 and Volkswagen e-Golf electric cars using Combined Charging System (CCS) DC fast charging

So the hybrid that's better today may not be better a few years down the road, because the grid is getting cleaner, but that hybrid will always emit what it did the day it rolled off the assembly line.

To reiterate the point of the map above, then: 97 percent of U.S. buyers today can emit less per mile by buying an electric car over any non-hybrid gasoline or diesel vehicle.

And that's just using grid data from 2014. Consider how much cleaner some of these grids will have gotten over the years you own your next car!


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