A new lifecycle analysis published in Science challenges the long-held belief that keeping an existing gasoline car on the road is always the greener choice. Researchers from UC Santa Cruz and UC Santa Barbara have found that, in most scenarios, replacing a functional combustion vehicle with a battery-electric vehicle (EV) results in lower overall emissions. Their findings suggest that the environmental benefits of early retirement for gas cars are more significant than previously thought.
Lifecycle Emissions: What the Study Shows
The study, conducted by J. Elliott Campbell and Roland Geyer, compared the emissions impact of continuing to drive a working gasoline vehicle versus scrapping it and replacing it with a new battery-electric vehicle. For a typical SUV on the average US electricity grid, retiring the combustion vehicle in its second year and switching to an EV reduced cumulative emissions over a 16-year period by 44%.
While manufacturing a new EV does create an initial carbon ‘bump,’ the study found that this is offset by the EV’s lower operating emissions in about three years. Across all scenarios tested, 92% resulted in lower emissions from early retirement of combustion vehicles, with fleet-average assumptions showing a 58% reduction.
Key Variables: Mileage, Battery Emissions, and Grid Mix
The researchers varied several factors in their analysis, including vehicle efficiency, annual mileage, battery manufacturing emissions, battery size, and the emissions intensity of regional electricity grids. Battery-production emissions ranged from 52 to 173 kilograms of CO₂e per kilowatt-hour, but this only shifted the net benefit by about 13 percentage points.
The most important factor was how much fuel the old vehicle would have burned if kept in service. The study identified annual mileage thresholds below which the emissions from manufacturing a new EV are not recovered: about 7,054 kilometers (~4,384 miles) for cars, 6,837 kilometers (~4,250 miles) for SUVs, and 10,794 kilometers (~6,710 miles) for trucks. The average scenario used roughly 20,000 kilometers (~12,400 miles) per year.
When EV Replacement May Not Be Greener
The study found that replacing efficient hybrids, plug-in hybrids, or lightly driven vehicles may not always result in lower emissions. For example, replacing a plug-in hybrid electric vehicle (PHEV) car with a battery-electric vehicle (BEV) increased emissions by 11% under certain assumptions, while the result for SUVs was nearly neutral.
Additionally, if an EV consumes more than 30 kWh per 100 kilometers and is charged from a grid with emissions above 500 kilograms of CO₂ per MWh, the climate advantage of replacement can disappear.
Competitor Comparison
The study’s findings align with earlier modeling from Resources for the Future, which found that targeting scrappage payments based on expected future emissions—rather than simply vehicle age—could halve the public cost per ton of emissions avoided. This approach contrasts with flat bounties that do not account for how much fuel a vehicle would have burned if left in service.
Historical Context and Regional Differences
The United States remains highly dependent on private automobiles. According to Prieto-Curiel and Ospina’s The ABC of mobility, 91.9% of trips in US and Canadian urban areas are by car, compared to 44.9% in Europe and 18.8% in East Asia. This car dependence persists even as cities grow larger.
Federal Reserve survey data shows that about two-thirds of lower-income Americans who recently acquired a vehicle bought used, and 78% of privately purchased used vehicles cost less than $10,000 (~AUD 14,129). Early scrappage of working vehicles could reduce the supply of affordable used cars in the future.
Why this matters
This new research provides strong evidence that, in most cases, scrapping a working gasoline vehicle for an EV leads to significant emissions reductions. The findings challenge the common argument that keeping an old car running is always the greener option, highlighting the importance of considering future fuel consumption and regional electricity emissions.
However, the study also underscores that not every vehicle is a good candidate for early retirement. Lightly driven cars, efficient hybrids, and vehicles in regions with high grid emissions may not deliver the same climate benefits from replacement.
What this means for buyers
For consumers considering the switch to an EV, the study suggests that replacing a high-mileage, less efficient gasoline vehicle is likely to yield the greatest environmental benefit. Those with lightly used or highly efficient vehicles may want to weigh the emissions from manufacturing a new EV against their actual driving needs.
Buyers should also consider their local electricity mix, as cleaner grids further improve the emissions advantage of EVs. Policymakers may look to these findings when designing future scrappage or incentive programs.
Key Specs
- Emissions reduction (SUV, 16 years, US grid): 44%
- Fleet-average emissions reduction: 58%
- Battery production emissions range: 52–173 kg CO₂e per kWh
- Annual mileage threshold (cars): 7,054 km (~4,384 miles)
- Annual mileage threshold (SUVs): 6,837 km (~4,250 miles)
- Annual mileage threshold (trucks): 10,794 km (~6,710 miles)
- Average annual mileage (study): 20,000 km (~12,400 miles)
- Grid emissions threshold (climate advantage lost): 500 kg CO₂ per MWh
Source
Images sourced from: amprius.com
