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Plug-in hybrid electric vehicles release nearly five times greater global warming emissions than official data indicate, according to a new report.

Widening Gap In Lab and Actual Emissions

Data shows that PHEVs release only one-fifth lower CO₂ than traditional gas and diesel vehicles, based on research carried out by a non-profit organization. This differs significantly with laboratory estimates, which suggested a three-quarters reduction in emissions.

Analysts studied data from onboard energy use monitors of eight hundred thousand cars sold in the EU from 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than lab estimates, up from 3.5 times in 2021.

“Real-world CO2 output are rising, while official figures are decreasing,” said a lead researcher participating in the study. “That discrepancy is growing and poses a significant problem. Consequently, PHEVs emit nearly as heavily as petrol vehicles.”

Primary Factors Behind the Emissions Gap

Researchers linked the majority of the difference to inflated estimates of the “electric driving share” – the percentage of miles driven in electric power compared to overall mileage. The team found that only 27% of driving was completed in EV mode, while lab estimates assumed over four-fifths.

Even, when operating in electric mode, emission amounts were significantly higher than official projections. This occurred because electric motors were insufficiently powerful sufficient to function independently, leading to combustion motors using fossil fuels for almost one-third of the distance completed in electric mode.

Regulatory and Economic Consequences

According to calculations, the lowballing of PHEV emissions enabled several large carmaker groups to avoid over €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ targets.

Furthermore, owners of PHEVs would spend about €500 more per year in running costs than is assumed under lab conditions.

“The strong claims that automakers like to make about their plug-in hybrid vehicles are obviously far from the mark,” stated a transport expert. “Buyers are being duped into believing that by buying a PHEV, they are benefiting the planet and saving money. Actually, PHEVs are only slightly better than standard petrol and diesel cars in terms of energy consumption, CO₂ emissions, and operating costs.”

Political Debate and Automotive Pressure

Hybrid cars have recently been brought again into policy debates as automakers have lobbied the European Union to weaken CO₂ targets. A proposed prohibition on sales of new internal combustion vehicles in 2035 has faced heavy pressure from the car sector and opposition from EU countries with large automotive manufacturing.

Several high-level officials have suggested PHEVs as a possible “flexibility” option to include in the legislation.

An independent energy policy expert, who was unaffiliated with the research, described the analysis a “very useful addition” after a long period in which parts of the car sector argued there was insufficient data to accurately assess real-world emissions.

“The results demonstrate, beyond any doubt, that the difference in lab and actual PHEV energy use and CO₂ output is significantly larger than for petrol or diesel vehicles,” the expert stated. “All regulatory changes concerning PHEVs should be made with utmost care and in the light of that evidence.”