Researchers J. Elliott Campbell of UC Santa Cruz and Roland Geyer of UC Santa Barbara published a study in Science comparing the emissions impact of keeping a functional gasoline vehicle versus retiring it early and replacing it with a battery-electric vehicle. The analysis varied vehicle efficiency, annual mileage, battery manufacturing emissions, battery size, and regional electricity emissions rather than assuming a single favorable case.
For a representative production-weighted SUV on the average U.S. grid, retiring the combustion vehicle in its second year and replacing it with an EV reduced cumulative emissions over a 16-year period by 44%. The manufacturing emissions of the replacement EV were repaid in roughly three years through lower operating emissions.
Across all tested combinations, 92% of scenarios showed lower emissions from early retirement, with fleet-average assumptions yielding a 58% benefit. The full range spanned an 82% reduction to a 77% increase in deliberately extreme cases, indicating replacement does not always win.
The study found that the amount of fuel the old vehicle would continue burning was the biggest driver of results, not the manufacturing emissions of the replacement battery. Varying battery-production emissions from 52 to 173 kilograms of CO₂e per kilowatt-hour shifted the net benefit by only about 13 percentage points, while differences in vehicle operating efficiency created more than twice as much variability.
Annual mileage thresholds were identified below which the EV's manufacturing emissions are not recovered: about 7,054 kilometers for cars, 6,837 kilometers for SUVs, and 10,794 kilometers for trucks. These are well below the roughly 20,000 kilometers in the average case, but lightly driven vehicles exist and may be better left in service.
Efficient hybrids, some plug-in hybrids, and cases where inefficient EVs are charged from particularly dirty grids are also poor candidates for early retirement. 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 megawatt-hour.
The authors note that destroying working vehicles early can remove affordable used cars from the market, since lower-income households predominantly buy used vehicles that have cascaded down from wealthier owners. A modern retirement program should target high-mileage, inefficient vehicles while supporting used EV supply and affordable transportation access.
Fleet turnover from governments, rental companies, and corporate fleets can accelerate emissions reductions while putting relatively young EVs into the used market. Battery-health certificates, dependable charging, and reasonable financing would make those vehicles more useful to secondhand buyers.
New Science Says Scrapping A Working Gas Car For An EV Is Usually Greener
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