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Plug-in hybrid electric vehicles release almost 5x more global warming emissions than lab-reported data indicate, according to a new analysis.

Growing Discrepancy Between Lab and Real-World Emissions

Data reveals that PHEVs release only 19% lower CO₂ than conventional gas and diesel cars, based on research conducted by a advocacy organization. That contrasts sharply with lab tests, which assumed a three-quarters reduction in pollution.

Analysts studied information from in-vehicle fuel consumption meters of 800,000 cars sold in Europe from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than official figures, increased from three and a half times in 2021.

“Real-world CO2 output are increasing, while official figures are decreasing,” stated a senior researcher involved in the report. “This discrepancy is growing and creates a serious issue. As a result, PHEVs emit almost as much as petrol vehicles.”

Key Factors Driving the Emissions Gap

Researchers attributed most of the gap to inflated estimates of the “electric driving share” – the percentage of kilometers driven in battery power compared to total mileage. The team determined that just a quarter of travel was done in electric mode, while lab estimates suggested over four-fifths.

Additionally, when running in electric mode, pollution levels were well above official estimates. This occurred because EV motors were insufficiently powerful sufficient to operate alone, leading to combustion motors using fossil fuels for nearly one-third of the travel completed in electric mode.

Regulatory and Financial Implications

According to estimates, the underestimation of PHEV emissions allowed four major automaker companies to avoid over €5bn in penalties from 2021 and 2023, by falsely simplifying compliance with EU average fleet CO₂ targets.

Additionally, owners of PHEVs would spend approximately €500 extra per year in running expenses than is estimated under laboratory conditions.

“The strong claims that automakers often promote about their plug-in hybrid cars are obviously far from the mark,” commented a transport analyst. “Buyers are being misled into thinking that by buying a PHEV, they are helping the environment and saving costs. In reality, PHEVs are little improved than standard gas and diesel vehicles in terms of fuel use, CO₂ production, and running costs.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have recently been drawn again into political debates as automakers have pressed the European Union to weaken CO₂ standards. A proposed ban on new internal combustion vehicles in 2035 has faced intense pressure from the car sector and opposition from member states with significant car industries.

Several senior politicians have suggested plug-in hybrids as a potential “compromise” solution to include in the regulation.

One external energy policy expert, who was not involved with the research, called the analysis a “highly valuable contribution” after a long period in which segments of the automotive sector claimed there was insufficient information to accurately evaluate real-world CO2 output.

“The results show, without question, that the gap in official and actual PHEV fuel consumption and CO₂ output is significantly larger than for petrol or diesel vehicles,” they stated. “Any regulatory changes regarding PHEVs should be made with extreme care and in the light of that evidence.”