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Plug-in hybrid cars release nearly five times greater global warming emissions than lab-reported figures indicate, according to a new analysis.

Growing Gap Between Official and Real-World Emissions

Data shows that PHEVs emit only one-fifth lower CO₂ than traditional petrol and diesel cars, based on analysis carried out by a advocacy group. That differs sharply with laboratory tests, which assumed a 75% decrease in pollution.

Analysts studied information from in-vehicle fuel consumption meters of 800,000 vehicles registered in the EU between 2021 and 2023. They found that real-world CO₂ output from PHEVs in 2023 were 4.9 times higher than lab estimates, increased from three and a half times in 2021.

“Real-world CO2 output are increasing, while official emissions are falling,” said a lead researcher participating in the study. “This discrepancy is widening and poses a serious problem. As a result, PHEVs pollute nearly as heavily as gasoline cars.”

Key Reasons Driving the Discrepancy

Researchers attributed the majority of the difference to overestimates of the “utility factor” – the ratio of kilometers driven in electric mode relative to overall mileage. The team determined that just 27% of travel was completed in electric mode, while official estimates assumed over four-fifths.

Additionally, when operating in EV mode, emission levels were significantly higher than lab estimates. This occurred because EV motors were not strong sufficient to function independently, resulting to combustion motors burning fossil fuels for nearly one-third of the distance covered in EV mode.

Policy and Economic Consequences

Based on estimates, the lowballing of PHEV emissions allowed several major carmaker companies to escape over €5bn in penalties between 2021 and 2023, by artificially easing compliance with EU fleet-average CO₂ targets.

Furthermore, drivers of PHEVs would pay about €500 extra annually in running costs than would be estimated under lab tests.

“The strong claims that manufacturers like to make about their PHEV cars are clearly far from the mark,” commented a automotive expert. “Consumers are being duped into thinking that by buying a PHEV, they are helping the planet and saving money. Actually, PHEVs are only slightly better than standard gas and diesel cars in terms of fuel consumption, CO₂ production, and operating expenses.”

Political Debate and Automotive Pressure

Plug-in hybrid vehicles have recently been drawn again into political discussions as carmakers have lobbied the European Union to weaken CO₂ standards. A planned ban on new combustion engine cars in 2035 has faced heavy lobbying from the car industry and opposition from EU countries with significant car industries.

Some senior officials have proposed PHEVs as a potential “compromise” option to include in the regulation.

An external energy policy specialist, who was unaffiliated with the study, described the report a “very useful contribution” after a long period in which segments of the car industry claimed there was insufficient information to accurately assess actual emissions.

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