In recent months, American drivers have felt the pain of increased prices at the gas pump. There's some evidence that may be fueling interest in greener ways of getting around. Battery electric cars, more commonly called electric vehicles or EVs, can be cheaper to own and operate than gas-powered internal combustion engine cars, and they offer considerable sustainability benefits. But just how much better for the planet are electric vehicles, really?
As it turns out, from a carbon emissions standpoint, you'd be better off sending a brand new internal combustion engine car directly to the scrap heap in order to replace it with a battery electric car. That's the surprising new finding from research led by the University of California, Santa Cruz, that explored the carbon footprint trade-offs of vehicle trade-ins.
Now, of course, the research team doesn't actually recommend scrapping a car you just bought, especially amidst a nationwide cost-of-living crisis. But for drivers who are already in the process of making a decision about future transportation, the new study, published in the journal Science, makes the sustainability case for EV ownership crystal clear.
"In some ways, I think this is really a definitive study about the carbon emissions benefits of EVs, because it shows that even in such an extreme scenario, the EV is still the obvious winner," explained UC Santa Cruz Environmental Studies Professor Elliott Campbell, lead author of the paper. "So if you're someone who's trying to decide whether or not to put money into keeping your gas car going, switching to an EV as soon as a financially viable opportunity comes up is absolutely the right thing to do for the environment."
High environmental stakes
This research comes at a time when transportation has recently become the largest source of carbon emissions in the U.S. Personal vehicles, in particular, are responsible for a larger share than all other forms of transportation combined.
Traditional cars have "internal combustion engines" that burn gasoline in order to produce the energy that turns the wheels. But when gasoline and other fossil fuels are burned, they produce large amounts of carbon emissions — exhaust gasses that build up in our atmosphere, trapping heat around our planet and causing climate change.
Given the scale of carbon emissions from personal internal combustion engine vehicles, one of the most effective solutions to addressing climate change is helping drivers switch to battery electric cars. Battery electric cars run on stored electricity and are recharged from the local power grid, like a cellphone or a laptop. The mix of energy sources used to produce that electricity varies by location and usually involves some amount of fossil fuels. But it can also include a significant amount of renewable energy and cleaner-burning fossil fuels, like natural gas.
Prior studies have shown that manufacturing and driving battery electric vehicles produces substantially less carbon emissions than internal combustion engine vehicles. So for climate-conscious consumers, the case for choosing an electric vehicle over a gas-powered vehicle for a new purchase has long been clear. What's trickier has been figuring out the best timing for retiring existing gas vehicles, in order to maximize the climate benefits.
A question of timing
Campbell first developed the idea for the current study while he was working on a different project, interviewing people about their perceptions of electric vehicles.
"This question of when to retire your current vehicle kept coming up," he recalled. "Some people said they thought it would be most sustainable to keep driving their current car until the wheels fall off, and others were really unsure what timing was best. But it seemed to be a question on many people's minds."
And, surprisingly, there wasn't existing research-based guidance.
"Personally, I'm someone who repairs and reuses just about everything," Campbell said. "Keeping gear going makes sense in so many contexts, but not in every context. Sometimes it's better to just make a shift to a newer, more efficient option, and it wasn't clear yet which was the case with transitioning to an EV."
Replacing a functional gas-powered vehicle with an EV might seem "wasteful" from a carbon emissions standpoint, because the process of manufacturing a new EV is energy intensive, resulting in carbon emissions that could have been avoided by simply keeping the current vehicle in service longer. But on the other hand, getting internal combustion engine vehicles off the road sooner, rather than later, means more mileage will ultimately be driven with fewer emissions.
So at what point do the emission reduction benefits of driving electric outweigh the drawback of manufacturing a new vehicle? That's what researchers set out to discover.
Comparing carbon emissions
Campbell and his coauthor, UC Santa Barbara Professor Roland Geyer, both specialize in finding answers to exactly these types of tricky sustainability questions. Campbell is an environmental engineer with a background in large-scale computer modeling of ecological impacts, while Geyer is an industrial ecologist with deep experience in systems of product manufacturing and consumption.
Together they worked to compare several different timelines for replacing an internal combustion engine vehicle with an EV. They calculated the percent difference in emissions that would result if a gas-powered vehicle was driven for its full useful life (about 16 years), or scrapped and replaced at earlier years.
To do this, they looked at how carbon emissions for more than 400 internal combustion engine and battery electric vehicle models were affected by different vehicle efficiencies, grid electricity sources, vehicle mileages, and battery electric vehicle manufacturing emissions and battery sizes.
Their results showed that the climate benefits were generally greatest when gas-powered vehicles were retired at year one, resulting in a 58% reduction in carbon emissions over a 16-year period. It typically took about three years for the lower emissions of driving a battery electric vehicle to offset the emissions required to produce it. Then the climate benefits added up quickly from there.
"What it comes down to is just that gas vehicles require so much more energy to operate," Campbell explained. "Only 20% of the energy in the gasoline that most of our cars burn actually goes toward moving the vehicle — the rest is just lost as heat. So it really puts internal combustion engines in a totally different class than EVs when it comes to efficiency, and that leads to a situation where you want to retire the gas-powered vehicle as soon as you can."
Diving into the details
The exact benefits of retiring any particular internal combustion engine vehicle vary based on location and the specific type of vehicle. But 92% of the scenarios that researchers modeled for replacing gas-powered or hybrid electric vehicles with battery electric vehicles before the end of the vehicle's useful lifespan achieved at least some overall reduction in carbon emissions.
Plug-in hybrid electric vehicles are a notable exception. While standard hybrid electric vehicles use an electric motor to capture and reuse energy from the gas-powered engine each time the vehicle slows down, plug-in hybrid electric vehicles have small batteries that can be charged from the electric grid, providing some all-electric driving range. As a result, they're efficient enough that replacing them early with battery electric models could actually result in increased emissions in some cases. Similarly, extremely low-mileage internal combustion engine vehicles — driven annually less than 7,054km for cars, 6,837km for SUVs, or 10,794km for trucks — are not worth replacing, from a carbon emissions standpoint.
The energy mix that powers your local electricity grid also affects whether retiring a gas-powered vehicle early makes sense. In areas with power grids that are exceptionally reliant on coal or other high-polluting fossil fuels, there's less of an emissions reduction benefit to driving electric. That makes it harder to offset the emissions cost of producing a new battery electric vehicle.
For example, if you own a traditional hybrid electric vehicle with class-leading efficiency, you'd want to think twice about replacing it early if your local electricity grid is in the bottom 33% for efficiency among total U.S. energy generation. To find out if that's the case, check whether your local grid has a CO2 emissions rate exceeding 970 lbs/MWh.
For the majority of the U.S., though, there are consistent benefits to early retirement of even the most fuel-efficient gas-powered cars. And for the most common internal combustion engine vehicle models sold in the U.S., replacing your car early offers carbon emissions reduction even on the dirtiest power grids.
Implications for policymakers
Overall, the study's results show that helping drivers transition from internal combustion engine vehicles to battery electric vehicles as quickly as possible is crucial for fighting climate change.
Many states, including California , have vehicle "scrap-and-replace" programs that offer financial incentives to make trading out vehicles more cost-effective. Increasing the amount of funding available through such programs could help put EV ownership within financial reach for more people. That's especially true when those subsidies can be stacked alongside rebates for purchasing EVs.
The paper's findings also demonstrate the potential benefits of expanding eligibility for scrap-and-replace programs to a wider range of internal combustion engine cars, beyond just the highest-emitting vehicles. The case for a broader approach could become even stronger in the coming years. As renewable energy grows to provide a larger share of U.S. electricity generation, the carbon emissions benefits of driving an EV will grow accordingly. And development of a strong EV battery recycling industry could significantly offset the initial carbon emissions associated with producing new EVs.
The sooner we can facilitate these transitions, the better protected our communities will be from the impacts of climate change, researchers say.
"The rate of climate change is accelerating, so the rate of climate action needs to accelerate too," Campbell said. "If states want to put more money into programs that encourage people who are on the fence about EVs to make that leap toward a newer, cleaner, more cost efficient car to own and operate, our results show that certainly makes sense from an emissions reduction point of view."
