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Plug-in hybrid cars produce nearly 5x more planet-heating emissions than official data show, according to a new analysis.

Widening Gap In Official and Real-World Emissions

Statistics shows that PHEVs emit only one-fifth less CO₂ than conventional petrol and diesel vehicles, according to analysis conducted by a advocacy group. That differs sharply with laboratory tests, which assumed a three-quarters reduction in pollution.

Analysts studied information from onboard fuel consumption monitors of 800,000 cars sold in the EU from 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, increased from three and a half times in 2021.

“Actual emissions are rising, while lab-reported emissions are falling,” said a senior researcher involved in the report. “That gap is growing and poses a serious problem. Consequently, PHEVs pollute almost as much as petrol cars.”

Key Reasons Driving the Discrepancy

Researchers attributed most of the gap to overestimates of the “electric driving share” – the percentage of kilometers driven in battery power compared to overall distance. The team determined that only a quarter of travel was completed in EV mode, whereas lab estimates assumed over four-fifths.

Additionally, when operating in electric mode, emission levels were well above official projections. This occurred because EV motors were insufficiently powerful enough to function independently, leading to combustion motors using gasoline for almost a third of the distance completed in EV mode.

Policy and Financial Implications

Based on estimates, the underestimation of PHEV CO2 output allowed four major automaker companies to escape more than €5bn in penalties from 2021 and 2023, by falsely easing compliance with EU average fleet CO₂ targets.

Furthermore, owners of PHEVs could pay approximately €500 extra per year in operating expenses than would be assumed under lab tests.

“The strong claims that automakers like to make about their PHEV vehicles are clearly way off the mark,” stated a transport analyst. “Consumers are being misled into thinking that by buying a PHEV, they are helping the environment and saving money. Actually, PHEVs are little better than regular gas and diesel cars in terms of fuel consumption, CO₂ production, and running expenses.”

Political Debate and Industry Lobbying

Plug-in hybrid vehicles have recently been brought back into policy discussions as carmakers have pressed the European Union to weaken CO₂ targets. A proposed prohibition on new internal combustion vehicles in 2035 has faced heavy pressure from the automotive sector and opposition from EU countries with significant automotive manufacturing.

Some high-level officials have proposed plug-in hybrids as a potential “compromise” solution to include in the legislation.

An external energy economics expert, who was unaffiliated with the research, described the analysis a “very useful contribution” after years in which segments of the car sector claimed there was insufficient information to properly assess actual CO2 output.

“The results show, beyond any doubt, that the gap between official and real-world PHEV energy use and CO₂ emissions is much, much larger than for gasoline or diesel cars,” the expert stated. “All regulatory changes regarding PHEVs should be made with extreme care and in the light of this data.”