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Plug-in hybrid cars emit nearly 5x greater global warming emissions than lab-reported figures show, according to a new report.

Growing Discrepancy Between Official and Real-World CO2 Output

Statistics shows that PHEVs release just one-fifth lower CO₂ than conventional gas and diesel vehicles, according to research carried out by a advocacy organization. That contrasts sharply with lab estimates, which suggested a three-quarters reduction in pollution.

Researchers studied data from in-vehicle fuel consumption meters of 800,000 cars registered in the EU from 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab figures, increased from 3.5 times in 2021.

“Real-world emissions are increasing, while official figures are decreasing,” said a senior researcher involved in the study. “That gap is widening and poses a serious problem. Consequently, PHEVs emit almost as much as petrol vehicles.”

Primary Factors Driving the Emissions Gap

Researchers linked the majority of the difference to inflated estimates of the “electric driving share” – the ratio of kilometers travelled in battery power relative to total mileage. The team determined that only a quarter of driving was done in electric mode, while lab estimates assumed over four-fifths.

Even, when operating in EV mode, emission amounts were well above official estimates. This occurred because electric motors were not strong enough to function independently, leading to combustion motors burning fossil fuels for nearly a third of the travel covered in EV mode.

Policy and Economic Implications

Based on calculations, the underestimation of PHEV CO2 output allowed several large carmaker companies to avoid over €5bn in fines between 2021 and 2023, by falsely easing compliance with European Union fleet-average CO₂ targets.

Additionally, owners of PHEVs would pay approximately €500 extra annually in operating expenses than is assumed under laboratory tests.

“The bold claims that automakers often promote about their PHEV vehicles are clearly way off the mark,” stated a transport expert. “Consumers are being duped into believing that by purchasing a PHEV, they are benefiting the environment and cutting money. In reality, PHEVs are only slightly better than standard petrol and diesel vehicles in terms of fuel use, CO₂ production, and operating expenses.”

Policy Discussion and Industry Lobbying

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

Some high-level officials have suggested PHEVs as a possible “flexibility” solution to include in the legislation.

An independent energy policy specialist, who was not involved with the study, called the analysis a “very useful contribution” after years in which parts of the automotive sector argued there was insufficient information to accurately assess real-world emissions.

“These findings show, without question, that the gap between lab and actual PHEV fuel consumption and CO₂ emissions is significantly greater than for gasoline or conventional vehicles,” the expert said. “All policy changes concerning PHEVs should be implemented with utmost caution and in the light of this evidence.”