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Plug-in hybrid cars release almost 5x greater global warming emissions than lab-reported data indicate, according to a recent report.

Widening Discrepancy Between Official and Real-World CO2 Output

Data shows that PHEVs release only 19% less CO₂ than conventional petrol and diesel vehicles, according to research conducted by a non-profit organization. That differs sharply with lab estimates, which suggested a three-quarters decrease in pollution.

Analysts examined information from onboard energy use monitors of eight hundred thousand cars registered in Europe from 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were 4.9 times greater than official figures, up from three and a half times in 2021.

“Actual emissions are rising, while lab-reported figures are decreasing,” said a lead analyst participating in the study. “That discrepancy is widening and poses a significant problem. Consequently, PHEVs emit nearly as heavily as gasoline cars.”

Primary Reasons Behind the Emissions Gap

Researchers linked the majority of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers driven in battery power compared to overall mileage. The team determined that just a quarter of driving was completed in electric mode, whereas lab estimates assumed over four-fifths.

Even, when running in EV mode, emission levels were significantly higher than lab estimates. That occurred because EV motors were not strong enough to operate alone, resulting to combustion motors burning gasoline for nearly one-third of the distance covered in EV mode.

Policy and Financial Implications

According to calculations, the underestimation of PHEV emissions enabled four large automaker groups to escape more than €5bn in penalties from 2021 and 2023, by falsely easing compliance with EU average fleet CO₂ standards.

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

“The bold claims that manufacturers like to make about their plug-in hybrid vehicles are obviously far from the truth,” commented a automotive expert. “Consumers are being misled into thinking that by buying a PHEV, they are helping the environment and saving costs. In reality, PHEVs are only slightly better than regular petrol and diesel cars in terms of fuel consumption, CO₂ production, and running expenses.”

Policy Discussion and Automotive Pressure

Hybrid vehicles have recently been drawn back into policy debates as carmakers have pressed the EU to weaken CO₂ standards. A proposed ban on new combustion engine vehicles in 2035 has faced heavy pressure from the automotive sector and opposition from EU countries with significant automotive manufacturing.

Several high-level politicians have proposed plug-in hybrids as a possible “compromise” option to introduce in the regulation.

An external energy policy specialist, who was unaffiliated with the research, called the report a “very useful addition” after a long period in which segments of the car industry claimed there was too little information to properly evaluate real-world emissions.

“These findings demonstrate, without question, that the difference in lab and real-world PHEV energy use and CO₂ output is much, much larger than for petrol or conventional cars,” they stated. “Any policy adjustments concerning PHEVs should be made with utmost care and considering that data.”