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Plug-in hybrid cars produce nearly five times greater global warming emissions than lab-reported data show, according to a new analysis.

Growing Gap Between Lab and Actual Emissions

Statistics reveals that PHEVs emit only 19% lower CO₂ than conventional gas and diesel cars, according to research carried out by a non-profit organization. This contrasts sharply with laboratory tests, which assumed a three-quarters reduction in emissions.

Analysts studied information from in-vehicle fuel consumption meters of 800,000 vehicles sold in Europe from 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than official estimates, up from three and a half times in 2021.

“Actual CO2 output are rising, while official figures are falling,” said a senior researcher participating in the report. “This discrepancy is growing and creates a serious issue. Consequently, PHEVs pollute nearly as much as petrol vehicles.”

Key Reasons Driving the Emissions Gap

Researchers attributed most of the difference to overestimates of the “electric driving share” – the percentage of kilometers driven in battery power compared to overall mileage. The team found that only 27% of travel was done in electric mode, whereas lab estimates assumed over four-fifths.

Additionally, when running in EV mode, emission levels were significantly higher than official estimates. That happened because electric motors were insufficiently powerful enough to operate independently, leading to combustion motors burning gasoline for almost one-third of the distance completed in electric mode.

Policy and Financial Consequences

Based on calculations, the lowballing of PHEV emissions allowed several large carmaker groups to escape over €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with European Union fleet-average CO₂ standards.

Additionally, owners of PHEVs could pay about €500 more annually in operating costs than is estimated under laboratory conditions.

“The bold claims that automakers like to make about their PHEV cars are obviously way off the mark,” stated a transport analyst. “Buyers are being misled into thinking that by buying a PHEV, they are helping the planet and saving costs. Actually, PHEVs are little better than regular petrol and diesel vehicles in terms of fuel use, CO₂ emissions, and operating expenses.”

Political Discussion and Industry Pressure

Plug-in hybrid cars have lately been brought back into policy debates as automakers have lobbied the European Union to relax CO₂ standards. A proposed ban on sales of new internal combustion vehicles in 2035 has faced intense pressure from the automotive sector and opposition from EU countries with large automotive manufacturing.

Some senior officials have suggested PHEVs as a possible “flexibility” solution to introduce in the legislation.

One independent energy economics expert, who was unaffiliated with the research, described the report a “highly valuable addition” after a long period in which parts of the car industry claimed there was too little data to accurately assess actual emissions.

“These findings demonstrate, beyond any doubt, that the gap in lab and real-world PHEV energy use and CO₂ output is much, much greater than for gasoline or diesel cars,” they said. “All regulatory adjustments regarding PHEVs should be made with utmost caution and considering that data.”