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Plug-in hybrid electric vehicles release nearly 5x greater global warming emissions than official data show, according to a new analysis.

Growing Discrepancy Between Lab and Actual Emissions

Data shows that PHEVs emit only one-fifth less CO₂ than conventional petrol and diesel vehicles, based on analysis conducted by a non-profit group. That contrasts sharply with lab estimates, which assumed a 75% decrease in pollution.

Analysts studied data from in-vehicle fuel consumption meters of 800,000 vehicles sold in the EU from 2021 and 2023. They found that actual CO₂ output from PHEVs in 2023 were 4.9 times higher than official figures, up from three and a half times in 2021.

“Real-world emissions are increasing, while official emissions are decreasing,” said a senior analyst participating in the study. “That gap is widening and creates a significant problem. Consequently, PHEVs emit nearly as much as gasoline vehicles.”

Key Factors Behind the Discrepancy

Analysts attributed most of the difference to inflated estimates of the “electric driving share” – the ratio of miles travelled in battery power compared to total mileage. They found that only a quarter of travel was completed in EV mode, while lab assumptions assumed over four-fifths.

Additionally, when running in electric mode, emission amounts were significantly higher than lab estimates. This happened because EV motors were not strong enough to function alone, resulting to combustion motors burning gasoline for nearly a third of the travel covered in electric mode.

Policy and Financial Implications

According to estimates, the underestimation of PHEV CO2 output allowed several major automaker companies to avoid more than €5bn in fines from 2021 and 2023, by artificially easing adherence with European Union fleet-average CO₂ targets.

Furthermore, owners of PHEVs would pay approximately €500 more per year in running costs than would be assumed under lab tests.

“The bold claims that manufacturers often promote about their PHEV cars are clearly far from the mark,” commented a automotive analyst. “Consumers are being duped into believing that by purchasing a PHEV, they are benefiting the environment and saving money. Actually, PHEVs are little improved than regular petrol and diesel vehicles in terms of energy consumption, CO₂ production, and running costs.”

Political Discussion and Industry Pressure

Plug-in hybrid vehicles have recently been brought again into political debates as carmakers have pressed the European Union to weaken CO₂ standards. A planned ban on new combustion engine vehicles in 2035 has faced intense lobbying from the car sector and resistance from member states with significant car manufacturing.

Some high-level officials have proposed plug-in hybrids as a potential “flexibility” option to include in the regulation.

One independent energy policy expert, who was not involved with the study, called the analysis a “very useful contribution” after a long period in which segments of the car sector claimed there was insufficient information to accurately evaluate real-world emissions.

“These findings show, without question, that the gap between lab and actual PHEV energy use and CO₂ emissions is significantly larger than for gasoline or conventional cars,” the expert stated. “All policy changes concerning PHEVs should be made with extreme care and in the light of this evidence.”