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Plug-in hybrid cars release nearly five times greater global warming pollution than official data indicate, according to a recent analysis.

Growing Gap In Lab and Actual Emissions

Data reveals that PHEVs emit only one-fifth less CO₂ than conventional gas and diesel cars, according to research conducted by a non-profit group. That contrasts significantly with lab tests, which assumed a three-quarters reduction in pollution.

Researchers studied information from in-vehicle energy use meters of 800,000 vehicles registered in Europe from 2021 and 2023. They found that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official figures, up from 3.5 times in 2021.

“Actual emissions are rising, while lab-reported emissions are decreasing,” said a senior researcher participating in the study. “This discrepancy is growing and poses a serious issue. Consequently, PHEVs emit almost as heavily as petrol cars.”

Primary Reasons Behind the Discrepancy

Researchers linked most of the difference to overestimates of the “utility factor” – the percentage of miles travelled in electric power relative to overall distance. The team found that only a quarter of travel was done in electric mode, whereas official estimates suggested over four-fifths.

Even, when operating in electric mode, pollution levels were well above lab estimates. That happened because electric motors were not strong enough to operate independently, leading to combustion motors using gasoline for nearly a third of the distance covered in electric mode.

Policy and Financial Consequences

Based on calculations, the underestimation of PHEV emissions allowed four large carmaker companies to avoid over €5bn in fines between 2021 and 2023, by falsely simplifying compliance with European Union average fleet CO₂ standards.

Additionally, owners of PHEVs could pay approximately €500 more annually in running expenses than would be assumed under laboratory conditions.

“The bold claims that automakers like to make about their plug-in hybrid vehicles are clearly way off the truth,” stated a transport analyst. “Consumers are being duped into thinking that by buying a PHEV, they are helping the planet and saving costs. Actually, PHEVs are little improved than regular gas and diesel vehicles in terms of energy use, CO₂ production, and operating expenses.”

Policy Debate and Industry Lobbying

Hybrid vehicles have lately been drawn again into political discussions as automakers have pressed the EU to relax CO₂ targets. A proposed ban on new internal combustion vehicles in 2035 has faced intense lobbying from the car sector and opposition from EU countries with large car manufacturing.

Some senior officials have suggested plug-in hybrids as a potential “compromise” solution to introduce in the regulation.

An external energy economics specialist, who was unaffiliated with the research, described the report a “highly valuable contribution” after a long period in which segments of the automotive industry argued there was too little data to properly evaluate real-world emissions.

“These findings show, beyond any doubt, that the difference in lab and real-world PHEV fuel consumption and CO₂ emissions is significantly larger than for gasoline or diesel cars,” they said. “All policy changes concerning PHEVs should be implemented with extreme caution and considering this evidence.”