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Plug-in hybrid cars emit nearly 5x more global warming emissions than lab-reported data indicate, according to a recent report.

Widening Discrepancy Between Official and Real-World CO2 Output

Data reveals that PHEVs release only one-fifth lower CO₂ than conventional gas and diesel cars, based on research conducted by a non-profit organization. That differs significantly with laboratory tests, which assumed a 75% decrease in emissions.

Analysts examined information from onboard energy use monitors of 800,000 vehicles sold in Europe between 2021 and 2023. The team found that actual CO₂ emissions from PHEVs in 2023 were nearly five times greater than official estimates, increased from three and a half times in 2021.

“Real-world CO2 output are rising, while official figures are falling,” said a senior researcher participating in the report. “That discrepancy is growing and creates a serious problem. As a result, PHEVs emit nearly as much as petrol vehicles.”

Primary Reasons Driving the Emissions Gap

Researchers attributed the majority of the gap to inflated estimates of the “utility factor” – the ratio of miles travelled in electric power relative to total distance. They found that just 27% of travel was completed in EV mode, while official assumptions suggested over four-fifths.

Even, when operating in EV mode, pollution levels were significantly higher than lab estimates. This occurred because electric motors were insufficiently powerful enough to function independently, resulting to combustion motors burning fossil fuels for nearly a third of the distance completed in electric mode.

Policy and Economic Consequences

According to calculations, the underestimation of PHEV emissions enabled several major automaker groups to avoid more than €5bn in fines from 2021 and 2023, by artificially simplifying compliance with EU average fleet CO₂ standards.

Additionally, owners of PHEVs could spend about €500 more per year in running costs than is assumed under lab conditions.

“The bold claims that automakers like to make about their plug-in hybrid vehicles are clearly far from the mark,” stated a transport analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are benefiting the planet and cutting money. Actually, PHEVs are little improved than regular petrol and diesel cars in terms of energy consumption, CO₂ emissions, and operating costs.”

Political Discussion and Automotive Lobbying

Hybrid cars have recently been drawn again into political discussions as carmakers have lobbied the European Union to relax CO₂ standards. A planned ban on sales of new internal combustion cars in 2035 has faced heavy pressure from the automotive sector and resistance from member states with significant automotive manufacturing.

Several senior politicians have proposed plug-in hybrids as a potential “flexibility” solution to include in the legislation.

An independent energy economics expert, who was unaffiliated with the research, described the analysis a “highly valuable addition” after years in which segments of the automotive sector argued there was too little information to accurately assess actual emissions.

“The results show, without question, that the difference in official and actual PHEV fuel consumption and CO₂ output is much, much greater than for gasoline or diesel cars,” they said. “All policy changes regarding PHEVs should be implemented with extreme care and in the light of this data.”