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Plug-in hybrid electric vehicles release nearly 5x more global warming emissions than lab-reported data indicate, according to a recent analysis.

Widening Gap Between Official and Real-World CO2 Output

Data reveals that PHEVs release just one-fifth less CO₂ than conventional petrol and diesel vehicles, based on analysis conducted by a advocacy organization. This contrasts significantly with lab tests, which suggested a three-quarters decrease in pollution.

Researchers examined information from onboard fuel consumption monitors of eight hundred thousand cars sold in the EU from 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times higher than lab figures, up from 3.5 times in 2021.

“Actual emissions are increasing, while lab-reported emissions are decreasing,” said a senior analyst involved in the study. “This gap is growing and poses a significant issue. As a result, PHEVs emit almost as heavily as petrol vehicles.”

Primary Reasons Driving the Discrepancy

Researchers attributed most of the gap to inflated estimates of the “utility factor” – the ratio of miles driven in electric mode compared to overall mileage. The team determined that only a quarter of driving was completed in electric mode, whereas official assumptions suggested 84%.

Additionally, when operating in electric mode, pollution levels were well above lab projections. That happened because EV motors were insufficiently powerful sufficient to operate independently, leading to engines burning gasoline for almost one-third of the travel covered in EV mode.

Regulatory and Economic Implications

According to calculations, the lowballing of PHEV CO2 output enabled several large automaker groups to avoid over €5bn in penalties between 2021 and 2023, by falsely simplifying compliance with EU fleet-average CO₂ standards.

Additionally, owners of PHEVs would spend about €500 extra annually in operating expenses than would be estimated under lab conditions.

“The strong statements that manufacturers often promote about their PHEV vehicles are clearly far from the mark,” stated a transport analyst. “Consumers are being duped into thinking that by buying a PHEV, they are helping the planet and saving costs. In reality, PHEVs are little improved than regular petrol and diesel cars in terms of fuel use, CO₂ production, and running expenses.”

Political Debate and Automotive Pressure

Plug-in hybrid vehicles have lately been brought back into political discussions as automakers have pressed the EU to weaken CO₂ targets. A proposed ban on new combustion engine cars in 2035 has faced intense pressure from the automotive industry and opposition from EU countries with significant car industries.

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

One independent energy economics expert, who was not involved with the research, described the analysis a “highly valuable addition” after years in which parts of the automotive sector argued there was too little information to properly assess actual emissions.

“The results show, beyond any doubt, that the gap in lab and real-world PHEV energy use and CO₂ emissions is much, much larger than for petrol or diesel vehicles,” they stated. “All policy changes regarding PHEVs should be made with extreme caution and considering that evidence.”