Lifecycle Scrapping Combustion Engines Almost Always Helps the Climate

Scrapping the combustion engine, buying an electric car, and thus doing something for the climate: According to an analysis, this can already be worthwhile even if the combustion engine vehicle is new.

Whoever scraps their roadworthy combustion engine vehicle and replaces it with a battery-electric vehicle improves the CO₂ balance in most cases—even if the combustion engine vehicle is new. This is the conclusion of a lifecycle study based on the stock of passenger cars, SUVs, and pickups in the United States and the regional structure of the U.S. power grid.

According to the analysis, passenger cars in the US produce more CO₂ emissions than the entire rest of the transportation sector combined, including air, rail, shipping, and truck traffic. The transportation sector is therefore the largest single source of greenhouse gases in the United States. The study's question: Is it climate-efficient to prematurely retire a functioning combustion engine vehicle, even though the production of an electric car causes more emissions than that of a comparable combustion engine vehicle?

92 Percent of Scenarios with Climate Advantage

For an average SUV with the US energy mix and an assumed lifespan of 16 years, the authors compare three scenarios: continuous use of the combustion engine, replacement in the eleventh year, and replacement in the second year. In the earliest scenario, cumulative emissions decrease by 44 percent; the additional "CO₂ debt" from battery production is offset after about three years.

Across the entire spectrum of US vehicle efficiencies, the effect ranges from an 82 percent reduction in emissions to a 77 percent increase—depending on the vehicle and charging power source. However, in 92 percent of the modeled cases, a net benefit was observed; for the average fleet efficiency, the savings amounted to 58 percent. The advantage can only reverse if an electric car consumes more than 30 kilowatt-hours per 100 kilometers while the regional power mix emits more than 500 kilograms of CO₂ per megawatt-hour.

Model Calculations with Real U.S. Vehicles

For production-weighted fleet averages and best-selling models—such as the comparison between the Ford F-150 and the electric Lightning version—savings of 55 to 57 percent were observed for passenger cars, SUVs, and trucks. For particularly efficient combustion engines and hybrids like the Toyota Prius, replaced by a Tesla Model 3, the advantage was smaller: 56 percent for passenger cars, 34 percent for SUVs, and 23 percent for trucks.

Replacing a plug-in hybrid with a pure BEV, on the other hand, brings hardly any advantages; for passenger cars, the model calculation even showed an 11 percent increase in emissions. To validate their findings, the authors compared their results with an independent dataset from the US Environmental Protection Agency (EPA) covering 459 vehicle models and obtained comparable values of 55, 57, and 47 percent for passenger cars, SUVs, and trucks.

Battery Production Less Important than Vehicle Efficiency

Across a range of 52 to 173 kilograms of CO₂ equivalent per kilowatt-hour of manufacturing emissions, the climate benefit fluctuated by only 13 percentage points. Only in the worst-case scenario—the replacement of a particularly fuel-efficient hybrid vehicle assuming the highest battery manufacturing emissions—did the benefit approach zero. The difference between a basic battery and a larger battery altered the result by only three percentage points.

For the best-selling vehicle models, the climate benefit remained consistent across all examined US grid regions. For particularly efficient hybrid vehicles, however, the advantage dropped to a minimum or reversed in regions with a grid intensity exceeding 400 kilograms of CO₂ per megawatt-hour. According to the study, such regions accounted for approximately one-third of total US electricity production at the time of investigation.

Resale Brings No Climate Advantage

The calculated break-even annual mileage, from which the manufacturing emissions of the battery-electric model are offset, is 7,054 kilometers (approx. 4,383 miles)  for passenger cars, 6,837 kilometers (approx. 4,248 miles) for SUVs, and 10,794 kilometers (approx. 6,707 miles) for trucks, according to the analysis—all significantly below the average U.S. annual mileage of around 20,000 kilometers (approx. 12,400 miles).

The authors explicitly point out in the analysis that the calculated climate advantage depends on the actual scrapping of the old vehicle. If the combustion engine model is instead resold, the additional used car supply could deter people from lower-emission alternatives such as public transport.

Disposal Often Uneconomical

Under current market conditions, scrapping a functioning, young combustion engine model is not economically attractive, according to the analysis. Existing incentive programs are insufficient for this purpose. However, the authors see significant potential for policy measures—such as expanded scrappage bonuses—to reduce the emissions of an increasingly long-lived fleet of combustion engine vehicles in the US. Another option identified by the study is the expansion of a reliable and equally accessible charging infrastructure in the US.

The authors of the study are Elliott Campbell from the Department of Environmental Studies, University of California, Santa Cruz, USA, and Roland Geyer from the Bren School of Environmental Science and Management, University of California, Santa Barbara, USA. The study was published in the journal Science.