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Plug-in hybrid cars produce nearly 5x more planet-heating emissions than lab-reported data show, according to a new report.

Growing Discrepancy Between Lab and Actual Emissions

Statistics shows that PHEVs emit just one-fifth lower CO₂ than traditional gas and diesel vehicles, according to analysis carried out by a advocacy organization. That contrasts significantly with lab estimates, which suggested a three-quarters reduction in pollution.

Analysts examined data from onboard energy use meters of 800,000 cars sold in Europe from 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab figures, up from three and a half times in 2021.

“Real-world CO2 output are increasing, while official figures are falling,” said a lead researcher involved in the study. “That discrepancy is growing and poses a serious problem. As a result, PHEVs pollute almost as heavily as gasoline cars.”

Key Reasons Behind the Emissions Gap

Analysts attributed most of the gap to overestimates of the “electric driving share” – the ratio of kilometers driven in battery power relative to overall mileage. The team found that just 27% of driving was completed in EV mode, while official assumptions assumed 84%.

Additionally, when running in electric mode, emission amounts were well above official estimates. This occurred because EV motors were not strong sufficient to function independently, leading to combustion motors using fossil fuels for nearly one-third of the distance covered in electric mode.

Regulatory and Economic Implications

Based on calculations, the lowballing of PHEV emissions enabled four major carmaker companies to escape more than €5bn in penalties between 2021 and 2023, by artificially simplifying compliance with EU average fleet CO₂ standards.

Furthermore, owners of PHEVs could pay about €500 extra annually in operating costs than would be assumed under lab tests.

“The strong statements that manufacturers often promote about their PHEV vehicles are clearly way off the truth,” stated a transport analyst. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the planet and saving costs. In reality, PHEVs are little improved than standard gas and diesel cars in terms of fuel consumption, CO₂ production, and operating expenses.”

Political Debate and Industry Pressure

Plug-in hybrid cars have recently been brought back into policy debates as automakers have lobbied the EU to weaken CO₂ standards. A proposed prohibition on sales of new combustion engine cars in 2035 has faced intense pressure from the car sector and opposition from member states with large car manufacturing.

Some senior politicians have suggested PHEVs as a potential “flexibility” solution to introduce in the regulation.

One independent energy policy specialist, who was not involved with the research, described the report a “highly valuable addition” after a long period in which segments of the car sector argued there was too little data to properly assess real-world emissions.

“The results show, beyond any doubt, that the difference between official and real-world PHEV fuel consumption and CO₂ emissions is much, much greater than for gasoline or diesel cars,” they said. “All policy changes regarding PHEVs should be made with utmost care and in the light of that evidence.”