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

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Replacing a working gasoline vehicle can create a short manufacturing carbon debt while avoiding years of much larger combustion emissions.

August 16, 20261 minute

Michael Barnard

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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...