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Plug-in hybrid cars release nearly five times greater planet-heating pollution than lab-reported data show, according to a new report.

Growing Discrepancy Between Official and Actual CO2 Output

Statistics shows that PHEVs release only one-fifth less CO₂ than conventional petrol and diesel cars, according to research carried out by a advocacy group. This contrasts sharply with laboratory tests, which assumed a 75% reduction in pollution.

Researchers examined data from in-vehicle fuel consumption monitors of 800,000 vehicles sold in Europe from 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official estimates, up from three and a half times in 2021.

“Real-world emissions are rising, while lab-reported emissions are falling,” said a lead analyst participating in the report. “This discrepancy is growing and poses a significant problem. As a result, PHEVs emit nearly as heavily as petrol cars.”

Primary Reasons Driving the Emissions Gap

Researchers attributed most of the gap to overestimates of the “electric driving share” – the percentage of miles driven in battery power compared to overall mileage. The team determined that just a quarter of travel was done in electric mode, whereas lab assumptions assumed over four-fifths.

Even, when operating in electric mode, pollution amounts were well above lab projections. That occurred because EV motors were insufficiently powerful sufficient to operate alone, resulting to combustion motors using gasoline for nearly one-third of the distance completed in EV mode.

Regulatory and Economic Consequences

According to calculations, the lowballing of PHEV CO2 output enabled several large carmaker groups to escape more than €5bn in fines between 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ standards.

Furthermore, owners of PHEVs would pay approximately €500 extra annually in running costs than is assumed under laboratory tests.

“The strong claims that automakers often promote about their PHEV vehicles are obviously way off the mark,” stated a transport expert. “Buyers are being duped into thinking that by purchasing a PHEV, they are helping the environment and cutting costs. Actually, PHEVs are only slightly improved than standard petrol and diesel cars in terms of fuel consumption, CO₂ production, and operating expenses.”

Political Discussion and Industry Lobbying

Hybrid vehicles have recently been drawn again into policy debates as automakers have lobbied the EU to relax CO₂ standards. A planned ban on sales of new internal combustion vehicles in 2035 has faced intense lobbying from the automotive industry and opposition from EU countries with large car manufacturing.

Some high-level officials have proposed PHEVs as a possible “compromise” option to introduce in the regulation.

One external energy policy expert, who was not involved with the study, described the report a “highly valuable addition” after a long period in which parts of the automotive industry argued there was insufficient information to accurately assess actual emissions.

“These findings show, beyond any doubt, that the gap in official and real-world PHEV fuel consumption and CO₂ emissions is much, much larger than for petrol or diesel vehicles,” they stated. “Any policy adjustments concerning PHEVs should be implemented with extreme caution and considering that evidence.”