New Science Says Scrapping A Working Gas Car For An EV Is Usually Greener

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“The greenest car is the one already built” has been one of the more durable arguments against replacing internal combustion cars with EVs. It sounds sensible enough. Manufacturing a new vehicle has a carbon cost, while continuing to drive an existing car avoids another manufacturing event. But that framing quietly treats all of the gasoline the existing car will burn over the rest of its life as if it were free of emissions.

In 2024, I argued that a modern version of Cash for Clunkers should pay people to retire internal combustion vehicles early when they replace them with electric ones. I described that as a strong opinion, weakly held because the lifecycle objection was obvious. If a gasoline car has already been manufactured and still works, perhaps keeping it running until the wheels fall off really is greener than building another vehicle to replace it.

J. Elliott Campbell of UC Santa Cruz and Roland Geyer of UC Santa Barbara have now done the lifecycle work that question needed. Their new study in Science compares continued operation of functional combustion vehicles with permanently scrapping them and replacing them with battery-electric vehicles. They vary vehicle efficiency, annual mileage, battery manufacturing emissions, battery size and regional electricity emissions instead of assuming one conveniently favorable EV case. Their results make the environmental case for early retirement considerably stronger than I expected.

For a representative production-weighted SUV on the average US grid, retiring the combustion vehicle in its second year and replacing it with a battery EV reduced cumulative emissions over the study’s 16-year period by 44%. Manufacturing the replacement EV creates the expected carbon bump, but the lower operating emissions repay that manufacturing debt in about three years. Earlier retirement produced the largest cumulative benefit because more years of gasoline combustion were avoided.

The broader sensitivity analysis is more important than that single SUV example. Across the combinations the researchers tested, 92% of modeled scenarios produced lower emissions from early retirement, while fleet-average assumptions produced a 58% benefit. The full range ran from an 82% reduction to a 77% increase in deliberately extreme cases, so this is not an argument that replacement always wins. It does, however, make clear that avoiding a second manufacturing event is much less decisive than the familiar slogan suggests.

The biggest driver in the study was how much fuel the old vehicle would continue burning, not the manufacturing emissions of the replacement battery. Campbell and Geyer varied battery-production emissions from 52 to 173 kilograms of CO₂e per kilowatt-hour, a very wide range, and that shifted the net retirement benefit by only about 13 percentage points. Differences in vehicle operating efficiency created more than twice as much variability.

There is a fairly straightforward accounting reason for that. The emissions from manufacturing the gasoline car are already in the atmosphere, so Campbell and Geyer treat them as sunk. The relevant comparison starts today: how much future gasoline will the old vehicle burn, and how does that compare with the manufacturing and electricity emissions of the EV that replaces it? Keeping the gasoline car avoids one new manufacturing event, but it also preserves years of recurring fuel consumption and combustion emissions.

That does not make every functioning gasoline vehicle a sensible candidate for the crusher. The study finds annual mileage thresholds below which the replacement EV’s manufacturing emissions are not recovered: about 7,054 kilometers for cars, 6,837 kilometers for SUVs and 10,794 kilometers for trucks. Those are well below the roughly 20,000 kilometers in the researchers’ average case, but very lightly driven vehicles clearly exist and can be better left in service.

Efficient hybrids and some plug-in hybrids are also poor targets, as are cases where inefficient EVs are charged from particularly dirty grids. In the continuous analysis, the climate advantage can disappear when EV electricity consumption exceeds roughly 30 kWh per 100 kilometers and grid emissions rise above 500 kilograms of CO₂ per MWh. Under the assumptions tested, replacing a PHEV car with a BEV increased emissions by 11%, while the SUV result was close to neutral. A policy that simply rewarded people for destroying any running combustion vehicle would ignore exactly the distinctions the study makes visible.

High-mileage pickups, inefficient SUVs and other vehicles burning a lot of fuel are much more attractive targets. That also lines up with earlier modeling from Resources for the Future, which found that targeting scrappage payments at expected future emissions rather than simply vehicle age could roughly halve the public cost per ton of emissions avoided. A flat bounty pays just as much to retire a lightly driven efficient car as it does to remove a heavily driven gas guzzler, which is convenient administratively but poor climate economics.

The United States then runs into a second problem that lifecycle analysis alone cannot solve. Americans are unusually dependent on private automobiles, including in large cities where people elsewhere shift much more strongly toward public transportation. Prieto-Curiel and Ospina’s The ABC of mobility found that 91.9% of trips in its US and Canadian urban sample were by car, compared with 44.9% in Europe and 18.8% in East Asia. It also found that US car dependence barely changed as cities became larger.

For a large share of Americans, access to a car is therefore less a consumer preference than a practical requirement for working, shopping, taking children to school, seeing a doctor and participating in society. That dependence matters because the cheap cars bought by lower-income households usually began life higher up the income ladder. Federal Reserve survey data cited in the Briefing found that about two-thirds of lower-income people who had recently acquired a vehicle bought used, while 78% of privately purchased used vehicles cost less than $10,000.

New vehicles bought or leased by wealthier households, companies, rental fleets and governments eventually become six-year-old, ten-year-old and fifteen-year-old vehicles, moving down through progressively cheaper portions of the market. Destroying a working vehicle early can therefore remove a future rung from that used-car ladder. The emissions benefit may be real, but so is the possibility that someone years later has one fewer affordable car available to buy.

Campbell and Geyer acknowledge that vehicle resale creates system effects, although their study is primarily a lifecycle analysis rather than a model of household transportation affordability. The policy problem is therefore broader than deciding whether a particular ICE vehicle produces fewer lifecycle emissions if it is scrapped. The United States also has to ensure that households which would have bought those cars farther down the depreciation curve still have affordable transportation available.

A modern vehicle-retirement program should be designed around both issues. Scrappage incentives should reflect fuel economy, recent mileage, remaining expected life and the local electricity mix rather than simply the age of the vehicle. Used EVs should qualify fully as replacements, with additional support for households that otherwise could not afford one. Efficient, lightly driven combustion cars should often be repaired rather than scrapped, while high-mileage pickups and SUVs deserve much stronger incentives for early retirement.

Fleet turnover is important as well. Governments, rental companies, delivery fleets and corporations rack up kilometers quickly, so electrifying them early gets a large immediate emissions benefit while also putting three-to-five-year-old EVs into the used market relatively quickly. Battery-health certificates, dependable charging and reasonable financing would make those vehicles much more useful to secondhand buyers. If supplies of sub-$10,000 or sub-$15,000 cars start tightening sharply in a region, the retirement incentive can be reduced rather than continuing to subsidize vehicle destruction regardless of what is happening in the used market.

That approach is more complicated than another Cash for Clunkers program, but the underlying climate case is now much firmer. Campbell and Geyer show that retiring a functioning combustion vehicle early can substantially reduce cumulative emissions, and that the most useful targets can be identified from mileage, efficiency and electricity emissions rather than guesswork. A high-mileage pickup burning a lot of gasoline is an obvious candidate. A Prius traveling 5,000 kilometers a year on a dirty grid probably is not.

The harder task for US policy is making the fleet turn over faster without treating affordable transportation as somebody else’s problem. That means retiring the vehicles responsible for the most future combustion while accelerating enough new and used EV supply that the bottom of the market becomes electric too. The climate transition and the used-car ladder do not have to work against each other, but getting both right requires considerably more thought than simply paying people to crush old cars.

I explore the study and what a smarter US vehicle-retirement policy could look like in TFIE Strategy Briefing.