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Plug-in hybrid electric vehicles release nearly 5x greater global warming emissions than lab-reported data indicate, according to a new report.

Widening Discrepancy In Lab and Real-World CO2 Output

Statistics shows that PHEVs emit only 19% lower CO₂ than conventional gas and diesel cars, according to research conducted by a advocacy group. This contrasts sharply with lab estimates, which assumed a 75% reduction in pollution.

Researchers examined data from in-vehicle fuel consumption monitors of eight hundred thousand vehicles registered in the EU between 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than lab estimates, up from three and a half times in 2021.

“Actual emissions are increasing, while official emissions are decreasing,” stated a lead analyst involved in the study. “That discrepancy is growing and creates a serious issue. As a result, PHEVs pollute nearly as much as petrol vehicles.”

Primary Reasons Driving the Emissions Gap

Analysts linked the majority of the gap to overestimates of the “electric driving share” – the ratio of kilometers driven in electric power relative to total distance. They found that only 27% of driving was done in EV mode, while lab estimates suggested over four-fifths.

Additionally, when operating in EV mode, emission amounts were well above lab projections. This happened because EV motors were insufficiently powerful sufficient to function alone, resulting to combustion motors burning fossil fuels for almost one-third of the travel completed in EV mode.

Regulatory and Economic Consequences

Based on estimates, the underestimation of PHEV CO2 output enabled four large automaker companies to avoid more than €5bn in fines from 2021 and 2023, by falsely simplifying compliance with EU fleet-average CO₂ standards.

Additionally, drivers of PHEVs could spend about €500 extra annually in operating costs than would be assumed under lab tests.

“The strong statements that automakers often promote about their PHEV vehicles are obviously way off the mark,” stated a automotive analyst. “Buyers are being misled into thinking that by buying a PHEV, they are benefiting the planet and saving money. In reality, PHEVs are little better than regular petrol and diesel cars in terms of energy consumption, CO₂ emissions, and operating costs.”

Political Debate and Industry Lobbying

Plug-in hybrid cars have recently been drawn again into policy debates as carmakers have lobbied the European Union to weaken CO₂ standards. A planned prohibition on new internal combustion cars in 2035 has faced heavy lobbying from the car industry and resistance from member states with large automotive manufacturing.

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

One independent energy economics specialist, who was not involved with the study, called the report a “very useful addition” after a long period in which parts of the car sector argued there was too little information to properly assess real-world emissions.

“The results show, without question, that the difference in official and real-world PHEV energy use and CO₂ emissions is much, much greater than for gasoline or conventional vehicles,” the expert said. “All policy changes concerning PHEVs should be made with utmost care and considering this data.”