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PHEVs release nearly 5x more global warming pollution than lab-reported data indicate, according to a recent report.

Growing Discrepancy Between Lab and Actual CO2 Output

Data shows that PHEVs emit just one-fifth less CO₂ than conventional gas and diesel vehicles, according to analysis carried out by a advocacy group. That contrasts sharply with laboratory tests, which suggested a three-quarters decrease in pollution.

Analysts studied data from in-vehicle fuel consumption monitors of eight hundred thousand vehicles registered in Europe between 2021 and 2023. The team discovered that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than lab figures, increased from three and a half times in 2021.

“Actual emissions are rising, while lab-reported emissions are decreasing,” stated a lead researcher involved in the study. “This discrepancy is widening and poses a significant problem. As a result, PHEVs emit nearly as heavily as gasoline cars.”

Primary Factors Driving the Emissions Gap

Researchers linked most of the difference to overestimates of the “electric driving share” – the percentage of miles travelled in battery power compared to total mileage. The team determined that just a quarter of travel was completed in EV mode, whereas official estimates suggested over four-fifths.

Additionally, when running in electric mode, pollution amounts were significantly higher than official estimates. That happened because EV motors were insufficiently powerful enough to operate alone, leading to combustion motors using gasoline for nearly one-third of the distance covered in electric mode.

Policy and Financial Implications

Based on estimates, the underestimation of PHEV CO2 output enabled four large automaker companies to avoid more than €5bn in penalties from 2021 and 2023, by falsely simplifying compliance with EU fleet-average CO₂ targets.

Furthermore, owners of PHEVs could pay about €500 more annually in running costs than is estimated under lab tests.

“The strong claims that manufacturers often promote about their PHEV cars are clearly far from the mark,” commented a transport analyst. “Buyers are being duped into thinking that by purchasing a PHEV, they are helping the planet and saving costs. Actually, PHEVs are only slightly improved than standard gas and diesel vehicles in terms of energy consumption, CO₂ production, and operating costs.”

Political Debate and Industry Pressure

Plug-in hybrid cars have recently been drawn again into policy debates as carmakers have lobbied the EU to weaken CO₂ standards. A proposed prohibition on new combustion engine cars in 2035 has faced heavy lobbying from the car industry and opposition from member states with significant automotive industries.

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

An independent energy policy expert, who was unaffiliated with the research, called the analysis a “highly valuable addition” after a long period in which segments of the car sector argued there was insufficient information to properly assess real-world CO2 output.

“These findings demonstrate, beyond any doubt, that the difference between lab and actual PHEV energy use and CO₂ output is much, much larger than for petrol or conventional vehicles,” the expert stated. “Any regulatory adjustments concerning PHEVs should be made with utmost care and considering this data.”