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Plug-in hybrid cars emit almost 5x greater planet-heating emissions than official figures indicate, according to a recent report.

Growing Discrepancy Between Official and Real-World CO2 Output

Data shows that PHEVs release just one-fifth lower CO₂ than traditional petrol and diesel cars, based on research carried out by a advocacy group. This contrasts significantly with lab tests, which suggested a 75% reduction in pollution.

Researchers examined data from onboard fuel consumption monitors of eight hundred thousand vehicles registered in the EU between 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, increased from 3.5 times in 2021.

“Actual CO2 output are increasing, while lab-reported emissions are decreasing,” said a senior researcher involved in the study. “That discrepancy is growing and poses a serious issue. As a result, PHEVs emit nearly as heavily as gasoline cars.”

Primary Factors Behind the Emissions Gap

Researchers linked most of the gap to inflated estimates of the “electric driving share” – the ratio of kilometers driven in battery power relative to total mileage. They found that only a quarter of travel was completed in EV mode, whereas official assumptions assumed 84%.

Even, when operating in electric mode, pollution levels were significantly higher than lab estimates. This occurred because electric motors were not strong enough to operate independently, leading to combustion motors burning fossil fuels for nearly a third of the distance covered in electric mode.

Regulatory and Economic Consequences

Based on estimates, the lowballing of PHEV CO2 output allowed several large automaker groups to avoid over €5bn in penalties from 2021 and 2023, by artificially simplifying compliance with EU average fleet CO₂ targets.

Furthermore, drivers of PHEVs could pay approximately €500 extra annually in operating expenses than would be estimated under lab conditions.

“The bold claims that automakers like to make about their plug-in hybrid cars are clearly far from the mark,” commented a automotive expert. “Buyers are being misled into believing that by purchasing a PHEV, they are benefiting the planet and cutting money. Actually, PHEVs are little better than standard gas and diesel vehicles in terms of fuel use, CO₂ production, and running costs.”

Political Debate and Industry Lobbying

Hybrid vehicles have recently been drawn again into policy debates as automakers have lobbied the European Union to weaken CO₂ targets. A planned ban on sales of new combustion engine vehicles in 2035 has faced heavy pressure from the car industry and opposition from member states with significant car industries.

Several high-level officials have suggested plug-in hybrids as a possible “compromise” solution to include in the regulation.

One external energy economics specialist, who was not involved with the research, called the report a “highly valuable addition” after a long period in which parts of the car industry argued there was insufficient information to properly assess real-world CO2 output.

“These findings show, without question, that the gap between official and real-world PHEV energy use and CO₂ emissions is much, much larger than for gasoline or conventional cars,” the expert stated. “Any policy changes concerning PHEVs should be made with utmost caution and in the light of that data.”