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Plug-in hybrid cars release nearly 5x more global warming emissions than official figures show, according to a new report.

Widening Discrepancy Between Lab and Real-World CO2 Output

Data shows that PHEVs emit just one-fifth lower CO₂ than traditional petrol and diesel cars, based on analysis conducted by a non-profit group. This contrasts significantly with laboratory tests, which assumed a three-quarters reduction in pollution.

Researchers examined data from onboard energy use monitors of eight hundred thousand cars registered in Europe from 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, up from three and a half times in 2021.

“Actual emissions are rising, while lab-reported figures are falling,” said a senior researcher involved in the study. “That gap is widening and creates a significant problem. As a result, PHEVs pollute almost as heavily as petrol vehicles.”

Primary Reasons Behind the Discrepancy

Researchers linked most of the gap to inflated estimates of the “electric driving share” – the percentage of miles driven in electric mode compared to total mileage. The team found that only a quarter of travel was done in electric mode, while lab estimates assumed over four-fifths.

Additionally, when running in electric mode, emission amounts were well above lab estimates. That occurred because EV motors were insufficiently powerful sufficient to operate alone, leading to engines using gasoline for almost one-third of the travel completed in EV mode.

Policy and Economic Consequences

According to estimates, the lowballing of PHEV emissions allowed four large automaker companies to escape over €5bn in penalties between 2021 and 2023, by artificially simplifying compliance with European Union fleet-average CO₂ targets.

Additionally, drivers of PHEVs could pay about €500 more per year in running expenses than would be estimated under lab tests.

“The bold claims that automakers like to make about their PHEV vehicles are clearly way off the truth,” stated a automotive analyst. “Consumers are being misled into thinking that by purchasing a PHEV, they are helping the planet and saving costs. In reality, PHEVs are only slightly improved than standard gas and diesel cars in terms of fuel use, CO₂ production, and operating expenses.”

Political Debate and Industry Lobbying

Plug-in hybrid cars have recently been brought back into political discussions as automakers have pressed the European Union to weaken CO₂ targets. A planned ban on sales of new internal combustion vehicles in 2035 has faced heavy lobbying from the car sector and opposition from member states with significant automotive industries.

Several senior politicians have suggested plug-in hybrids as a possible “flexibility” option to introduce in the regulation.

One independent energy economics specialist, who was not involved with the study, called the report a “highly valuable addition” after years in which parts of the automotive industry claimed there was too little information to properly evaluate real-world emissions.

“The results demonstrate, beyond any doubt, that the difference in lab and real-world PHEV fuel consumption and CO₂ emissions is much, much greater than for petrol or conventional cars,” they said. “Any policy changes concerning PHEVs should be made with extreme care and considering this evidence.”