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A photo of an electric car

A Nissan Leaf charges at an electric vehicle charging station in Portland, Oregon. But without steps to clean up power plant pollution, EVs won't drive down carbon emissions, a new study concludes.


Josie Garthwaite

for National Geographic

Published February 25, 2014

Electric cars can help limit reliance on imported oil and take a bite out of air pollution from urban traffic jams. But as sure-fire ammunition against climate change, a new study finds, they come up short.

The study attempted to take a big-picture view, analyzing the ripple effects of electric vehicles on the U.S. energy system, including possible changes in emissions of key air pollutants like heat-trapping carbon dioxide. The team of researchers, led by Joseph DeCarolis, assistant professor of civil, construction, and environmental engineering at North Carolina State University, created a model to look at the complex interplay among fuel prices, battery costs, government policies, and adoption of electric cars in the coming decades.  (See related quiz: What You Don't Know About Cars and Fuel.)

The team modeled 108 scenarios, calculating not only future levels of CO2 expected to spew from tailpipes, but also emissions of sulfur dioxide and nitrogen oxides from factories, power plants, and other sources. In a paper published in the peer-reviewed journal Environmental Science and Technology, the team reported that even in scenarios that yield the highest levels of EV deployment (high oil prices, low battery costs), plug-ins and hybrids would make up no more than 42 percent of all U.S. passenger vehicles in 2050 and would reduce overall emissions by a slim margin.  (See related: "Pictures: Cars That Fired Our Love-Hate Relationship With Fuel.")

The new model, developed and refined over nearly four years, comes at a time of rising stakes for understanding just how electric vehicles are likely to affect future emissions. Worldwide, plug-in vehicle production is expected to rise 67 percent this year to more than 403,000 cars, according to the latest forecasts from IHS Automotive. In China, the government announced plans this month to extend subsidies for electric cars as part of a larger effort to address air pollution so severe in some cities that they have prompted emergency measures to tackle the problem.  (See related, "Harbin Smog Crisis Highlights China's Coal Problem," and  "China's Electric Car Drive: Impressive, But Not Enough.")

But simply put, the North Carolina researchers concluded that electric cars have little ability to make a dent in overall emissions on their own.

"It's possible that the emissions benefits won't materialize under some future conditions," DeCarolis said. "This should hardly be controversial."

Some EV advocates are concerned that the new study might be misinterpreted, and used as ammunition against policies to encourage electrification of transportation. But they generally agree that efforts to cut vehicle emissions through deployment of cars have to go hand-in-hand with other policies to cut greenhouse gases, most notably, cutting emissions from power plants.

Only One Slice of the Pie

A key reason that EVs can only go so far as a solution is because passenger cars and light trucks contribute only about one-fifth of U.S. greenhouse gas emissions. So even if that one slice of the pie were eliminated (and carbon emissions from cars and light trucks dropped to zero), four slices would remain and the big carbon producers would press on. Also, tailpipe emissions don't tell the whole story: If the power grid is dirty enough, then charging an electric car can be more polluting than a fuel-efficient gas car.

The benefits of electric vehicles vary from place to place, season to season, and even time of day, depending on the percentages of electricity produced from zero-emission sources like wind, solar, hydropower, and nuclear, versus coal or natural gas.

The Union of Concerned Scientists (UCS) has made essentially the same point in its research on EV emissions. But Dave Reichmuth, a senior engineer in UCS's Clean Vehicles Program points out that charging and driving an electric car anywhere in the United States today produces fewer greenhouse gas emissions overall than an average compact gas vehicle.

Still, Reichmuth, who was not involved in the new study, agreed with the North Carolina researchers' point that EVs cannot be considered in isolation. "We know that lower battery costs lead to increased use [of electric vehicles], and cleaner electricity increases the benefits," he said. "It's important to look at electric vehicles as one important part of solutions" to address greenhouse gas emissions, along with biofuels, more efficient gas cars, fuel cell vehicles, and cleaner electricity.  (See related: "Pictures:  Seven Ingredients for Better Electric Car Batteries.")

But in reality, Reichmuth said, federal and state governments are putting into place multiple policies that can function in tandem to boost the benefits of EVs. "In California, we have a renewable portfolio standard for our electric grid, and a number of policies for vehicles," he said. "All of those policies work together."

The Consumer Variable

The North Carolina researchers modeled EV emissions under two potential U.S. policies: a renewable energy portfolio standard and a cap on carbon emissions. But there are variables too uncertain to model, including, notably, consumer choice. "Strong and persistent reluctance on the part of consumers," the researchers write, could "dampen or eliminate" the adoption trends predicted in their scenarios.

Even less clear is how advances outside the battery itself—weight reductions and efficiency improvements, for example—might diminish the influence of battery costs by making it possible for smaller batteries to power longer trips. (See related "Quiz: What You Don't Know About Batteries.") This is an important factor, given that consumers are likely, according to the researchers, to base decisions about which car to buy largely on the cost-effectiveness of one technology relative to another.

In the United States, fuel economy standards set to phase in from 2016 demand that automakers slash greenhouse gas emissions from cars and trucks by half by the 2025 model year—an achievement that industry experts say will require some use of electric drive.  (See related: "Pictures: A Rare Look Inside Carmakers' Drive for 55 MPG.") And current U.S. policies, such as tax credits of up to $7,500 for new plug-in vehicle purchases and a pledge to see one million all-electric cars deployed by 2015, are meant to promote adoption of electric cars.

But ultimately, if the goal is to reduce overall emissions, the study authors write, "it is not enough simply to incentivize the purchase of [electric vehicles] and wait for emissions benefits to accrue." They urge policymakers to be mindful of "evolving changes in the broader energy system" over time, noting that the largest and most consistent drop in emissions of carbon, sulfur dioxide, and nitrogen oxides across the dozens of scenarios tested came from a federal mandate to reduce carbon emissions nationwide.

Cleaner electricity can also reduce emissions, including those from electric vehicle charging, and the North Carolina team sees promise in a carbon pollution standard slated for proposal in 2014 that would seek to limit emissions from existing power plants. (See related, "New U.S. Limits on Power Plants: Five Points.")

"I think the take-home point is that the future is fraught with uncertainty, so simple policy actions such as tax credits for alternative vehicles do not necessarily lead to the desired outcome," DeCarolis said. "The conclusion should certainly not be that electric drive vehicles are bad for the environment."

This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.

Tom Radecki
Tom Radecki

5000 watts of US-made PV solar panels with a 25-year guarantee can be bought today for $5600 from Amazon.  That's only $4000 with the tax credit. Even in cloudy NW PA, this should generate 7000 kWh of electricity per year.  I saw a 3-day do-it-yourself installation course available for $175.  The actual installation takes 2 weeks.

One kWh will power a Nissan Leaf for 3 miles.  My son and I currently use 3500 kWh per year for our home.  The remainder of the will power the Leaf considerably more than we currently drive. The car's battery can power the house at night and I'll be able to charge it at home or at my office with solar power. 

Another set of at home panels could easily replace the natural gas energy we use for heating our small house to 60F daytime, 47F nighttime with enough left over energy to feed into the grid to offset the footprint of our food.  We work out daily to an intense sweat at the Y and just towel off vigorously, so we have no need for a hot water heater.  We hang dry our laundry already, so we haven't repaired the broken clothes dryer.  We don't use a dish washer and just heat water in the microwave. We wash clothes in cold water. We don't own AC, just fans. No one in America had AC when I was growing up in the 1950s and no one complained that they didn't have it.   I do like my heating blanket.

I see no reason why everyone in the U.S. can't reduce their footprint to zero right now.  I hope to do the above this later this year.  It is something we must do, so let's just do it.  The coming climate change disaster is going to be much worse than World War II, so let's act like it and make a few small changes and sacrifices.  In fact, the cost of reducing our footprint to zero is minor.  In the U.S. we are blessed with great sunshine.  Let's use it.  Some parts of our country have great wind resources, too. We need a good, stiff carbon tax which is returned to the public to wake people up.  

It has been estimated that one more human being will die this century for every 150 tons of carbon dioxide pollution.  The deaths will be mostly from starvation.  Each American generates 16 tons per year or is killing one more person every 10 years. Wake up America. Wake up.

peter horbatko
peter horbatko

Remember they were here before , what happened ? Profit  , quick profit . look how long it took to get on to recycling . Today with the way things are we are in a survival mode . With the government ( WE ) are going in all sorts of directions  . The only time energy issues come about is finding the money for gas .   

Steve Factor
Steve Factor

It has actually been very easy for me to eliminate a large portion of the pollution I used to contribute. An electric vehicle and a small solar array on my garage provides plenty of power for 90% of my previous electricity and gasoline usage. Electric vehicles alone cannot reverse the pollution damage we cause every year. That much should be obvious without a scientific study. Electric vehicles are however an essential part of the solution.

Daniel Phelan
Daniel Phelan

That's funny. Also, it is well known that cleaning up the power plants will do a great deal to cut pollution emissions. So this "study" just seems to state the obvious.

The benefits to the environment electric vehicles can bring are also many and obvious.

Roger Bird
Roger Bird

Unless of course those electric vehicles are powered by cold fusion or LENR.  And this IS going to happen.  You can bank on it.

Unlike the free energy embarrassment named Mark Goldes and his unicorn ideas.

Mark Goldes
Mark Goldes

Technology based on unrecognized science is emerging and will inexpensively create a fast-track to help replace all fossil and radioactive fuels.

A NO FUEL PISTON ENGINE will run 24/7 on atmospheric heat. Atmospheric heat is solar. It contains many thousands of times the total energy available from all of the fossil fuels. This untapped source of energy can at last be utilized. See to understand why and how.

The science is discussed in SECOND LAW SURPRISES on that site. It is difficult for most scientists to believe it is possible to circumvent the Second Law of Thermodynamics in suitably designed heat engines.

These engines will be followed by FUEL-FREE TURBINES. Large examples can supersede existing turbines in all types of power plants including those burning coal or nuclear fuel.

A few trolls post extensive rants in the erroneous belief that these claims reflect dishonesty and fraud. Prototypes validated by independent laboratories will prove them wrong.

Desktop examples will be followed by 1,000 watt emergency generators and home power units. FUEL-FREE TURBINES also promise hybrid cars and trucks with unlimited range, able to sell power to utilities when suitably parked, perhaps eventually paying for themselves. No wires needed. Variations will power aircraft.

Completing the prototypes and rapidly bringing these remarkable engines into mass production is the remaining challenge.

Celtic Solar
Celtic Solar

This study has repeatedly been quoted in the press as saying that EVs won't reduce CO2. This is not what it says. It says if EVs were primarily powered by coal, then there would be no reduction. The US is about 50% coal powered and portions with hydro and wind are far less coal powered. The Union of Concerned Scientists did a comprehensive well-to-wheel study and found that EVs reduce CO2 production in all 50 states. Note that electricity is used to refine gasoline too. So there is already CO2 in the air for each gallon of gas before you even put it in your car. If CO2 is a concern for you, buy an EV and put solar panels on your roof. There you go, CO2-free driving.

Keith Malone
Keith Malone

It does not appear that this study takes into account fuel cell electric vehicles that use hydrogen gas.  [Disclosure: I work for the California Fuel Cell Partnership.] 

Darell Dickey
Darell Dickey

Indeed. Difficult for scientists to "believe" that is possible to ignore reality.

Cameron Spitzer
Cameron Spitzer

There's that perpetual motion scammer again.  Please go away mr. scammer.

Bill Collins
Bill Collins

Key words being "unrecognized science"...

Darell Dickey
Darell Dickey

@Keith Malone  I assume this is due to mass adoption of FCV being so unlikely (due to the common, logical concerns of infrastructure, cost and efficiency) while we witness a blistering pace of BEV adoption.

I remember driving by the CFCP in it's heyday and seeing all the activity. Getting a bit sparse over there these days, it seems!

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