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Plug-in hybrid cars release almost five times greater planet-heating pollution than official data indicate, according to a recent analysis.

Widening Discrepancy Between Official and Real-World CO2 Output

Data shows that PHEVs emit just one-fifth less CO₂ than conventional gas and diesel vehicles, based on analysis carried out by a non-profit organization. That contrasts significantly with lab estimates, which suggested a three-quarters reduction in pollution.

Researchers examined information from onboard energy use monitors of 800,000 vehicles sold in the EU from 2021 and 2023. The team found that actual CO₂ emissions from PHEVs in 2023 were nearly five times higher than official figures, up from 3.5 times in 2021.

“Actual CO2 output are rising, while lab-reported figures are falling,” said a lead analyst participating in the report. “This discrepancy is widening and poses a serious issue. As a result, PHEVs emit almost as much as gasoline cars.”

Key Factors Behind the Emissions Gap

Researchers attributed the majority of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers driven in battery power compared to total distance. They found that just 27% of travel was completed in EV mode, while lab assumptions assumed 84%.

Additionally, when operating in electric mode, emission levels were significantly higher than lab estimates. That occurred because EV motors were insufficiently powerful enough to operate independently, leading to combustion motors burning gasoline for almost a third of the distance covered in EV mode.

Policy and Financial Consequences

According to estimates, the underestimation of PHEV emissions enabled several major carmaker groups to escape more than €5bn in fines between 2021 and 2023, by falsely simplifying compliance with European Union fleet-average CO₂ standards.

Additionally, drivers of PHEVs would spend approximately €500 more per year in operating expenses than is assumed under laboratory tests.

“The strong claims that manufacturers often promote about their plug-in hybrid vehicles are obviously way off the mark,” commented a automotive expert. “Consumers are being duped into believing that by purchasing a PHEV, they are helping the planet and saving costs. Actually, PHEVs are only slightly improved than standard petrol and diesel cars in terms of energy use, CO₂ production, and running expenses.”

Policy Debate and Industry Lobbying

Plug-in hybrid vehicles have recently been brought back into political debates as carmakers have pressed the European Union to weaken CO₂ standards. A planned ban on new internal combustion vehicles in 2035 has faced heavy pressure from the automotive sector and opposition from EU countries with significant car manufacturing.

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

An external energy policy expert, who was unaffiliated with the study, called the report a “very useful addition” after years in which parts of the automotive sector argued there was too little data to properly assess actual emissions.

“The results show, without question, that the gap between official and real-world PHEV energy use and CO₂ emissions is much, much larger than for petrol or diesel cars,” the expert stated. “Any policy adjustments regarding PHEVs should be made with extreme care and in the light of that data.”