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Plug-in hybrid electric vehicles produce nearly five times more global warming emissions than official figures indicate, according to a new analysis.

Widening Gap In Lab and Actual CO2 Output

Data shows that PHEVs emit just 19% less CO₂ than traditional petrol and diesel cars, based on research carried out by a advocacy group. This contrasts sharply with lab tests, which assumed a three-quarters reduction in pollution.

Researchers examined data from in-vehicle fuel consumption monitors of 800,000 vehicles sold in Europe from 2021 and 2023. The team discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than official figures, up from 3.5 times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are decreasing,” said a lead researcher participating in the study. “This discrepancy is widening and creates a serious problem. As a result, PHEVs pollute almost as much as petrol cars.”

Primary Factors Driving the Discrepancy

Researchers linked the majority of the gap to overestimates of the “utility factor” – the ratio of miles travelled in electric power compared to total mileage. The team determined that just a quarter of driving was done in EV mode, while official estimates assumed 84%.

Additionally, when operating in EV mode, emission levels were significantly higher than lab estimates. This occurred because EV motors were insufficiently powerful sufficient to function alone, resulting to combustion motors using fossil fuels for nearly one-third of the travel completed in EV mode.

Regulatory and Economic Consequences

According to calculations, the underestimation of PHEV CO2 output allowed several major carmaker companies to escape over €5bn in penalties between 2021 and 2023, by falsely easing compliance with EU fleet-average CO₂ targets.

Additionally, drivers of PHEVs would spend about €500 extra annually in operating expenses than is estimated under laboratory conditions.

“The bold statements that manufacturers like to make about their PHEV cars are clearly far from the truth,” stated a automotive analyst. “Buyers are being duped into believing that by purchasing a PHEV, they are helping the environment and cutting costs. In reality, PHEVs are only slightly better than regular petrol and diesel vehicles in terms of energy use, CO₂ emissions, and running expenses.”

Policy Debate and Industry Pressure

Plug-in hybrid vehicles have lately been drawn back into policy debates as automakers have pressed the EU to weaken CO₂ standards. A planned ban on sales of new combustion engine vehicles in 2035 has faced heavy pressure from the automotive industry and resistance from member states with significant automotive industries.

Several high-level officials have proposed PHEVs as a potential “flexibility” solution to include in the regulation.

One independent energy economics specialist, who was not involved with the study, called the report a “highly valuable contribution” after a long period in which segments of the automotive industry argued there was insufficient data to properly evaluate actual emissions.

“These findings demonstrate, without question, that the difference in official and real-world PHEV fuel consumption and CO₂ output is significantly larger than for petrol or conventional vehicles,” they said. “Any policy changes concerning PHEVs should be made with utmost care and considering this data.”