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PHEVs emit nearly five times more planet-heating pollution than official data indicate, according to a new analysis.

Growing Gap Between Official and Actual CO2 Output

Data shows that PHEVs release only 19% less CO₂ than traditional gas and diesel vehicles, according to research carried out by a non-profit organization. This differs significantly with lab estimates, which assumed a three-quarters reduction in pollution.

Researchers studied information from in-vehicle energy use meters of eight hundred thousand vehicles sold in the EU from 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, increased from three and a half times in 2021.

“Real-world CO2 output are increasing, while official figures are falling,” said a senior researcher involved in the report. “This discrepancy is widening and creates a significant problem. Consequently, PHEVs emit nearly as heavily as gasoline vehicles.”

Key Factors Driving the Emissions Gap

Researchers linked the majority of the difference to overestimates of the “utility factor” – the ratio of kilometers driven in electric power relative to overall mileage. The team determined that only a quarter of driving was done in electric mode, whereas official estimates assumed over four-fifths.

Additionally, when running in electric mode, emission amounts were well above official estimates. This happened because EV motors were insufficiently powerful sufficient to function alone, leading to engines burning fossil fuels for almost one-third of the travel covered in electric mode.

Policy and Economic Consequences

Based on calculations, the underestimation of PHEV emissions allowed four large carmaker companies to escape over €5bn in penalties from 2021 and 2023, by falsely simplifying adherence with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs would pay about €500 more annually in running expenses than would be assumed under laboratory conditions.

“The bold claims that automakers often promote about their PHEV vehicles are obviously way off the mark,” stated a transport analyst. “Consumers are being duped into thinking that by buying a PHEV, they are benefiting the environment and saving money. In reality, PHEVs are only slightly better than standard petrol and diesel vehicles in terms of fuel consumption, CO₂ emissions, and operating costs.”

Political Discussion and Industry Lobbying

Plug-in hybrid vehicles have recently been drawn back into policy debates as automakers have lobbied the EU to relax CO₂ standards. A planned prohibition on new combustion engine vehicles in 2035 has faced intense pressure from the car sector and opposition from member states with significant car industries.

Several senior officials have proposed plug-in hybrids as a possible “flexibility” option to include in the legislation.

An independent energy policy expert, who was unaffiliated with the study, called the report a “highly valuable contribution” after a long period in which segments of the car industry argued there was too little data to properly assess real-world CO2 output.

“The results demonstrate, beyond any doubt, that the gap between lab and actual PHEV energy use and CO₂ emissions is significantly larger than for gasoline or diesel cars,” they said. “Any regulatory adjustments concerning PHEVs should be implemented with extreme care and considering this data.”