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Plug-in hybrid cars release nearly 5x more planet-heating pollution than lab-reported figures show, according to a new analysis.

Widening Discrepancy In Official and Actual CO2 Output

Data reveals that PHEVs release only one-fifth less CO₂ than conventional petrol and diesel cars, based on research carried out by a non-profit organization. This differs significantly with laboratory tests, which suggested a three-quarters reduction in pollution.

Researchers studied data from onboard energy use meters of 800,000 cars sold in Europe between 2021 and 2023. The team found that actual CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, up from 3.5 times in 2021.

“Real-world CO2 output are rising, while lab-reported figures are falling,” stated a senior researcher participating in the study. “This discrepancy is growing and creates a serious problem. Consequently, PHEVs pollute nearly as heavily as petrol cars.”

Primary Factors Behind the Emissions Gap

Researchers linked the majority of the gap to inflated estimates of the “utility factor” – the percentage of miles travelled in electric power compared to total mileage. They found that only a quarter of driving was done in EV mode, whereas official estimates assumed over four-fifths.

Additionally, when running in EV mode, emission amounts were well above official estimates. That happened because electric motors were insufficiently powerful enough to operate independently, leading to combustion motors using gasoline for nearly a third of the travel completed in electric mode.

Policy and Financial Consequences

Based on estimates, the lowballing of PHEV emissions allowed four large carmaker companies to avoid over €5bn in fines between 2021 and 2023, by falsely simplifying adherence with European Union fleet-average CO₂ targets.

Furthermore, owners of PHEVs could pay about €500 more per year in operating costs than would be estimated under lab conditions.

“The strong claims that automakers often promote about their plug-in hybrid vehicles are clearly way off the truth,” stated a transport analyst. “Consumers are being misled into thinking that by buying a PHEV, they are benefiting the planet and saving money. Actually, PHEVs are little improved than regular gas and diesel vehicles in terms of fuel use, CO₂ production, and operating costs.”

Policy Discussion and Industry Pressure

Plug-in hybrid vehicles have recently been drawn back into policy debates as carmakers have lobbied the EU to weaken CO₂ targets. A planned ban on sales of new combustion engine vehicles in 2035 has faced heavy lobbying from the car sector and resistance from EU countries with significant car manufacturing.

Several senior officials have proposed plug-in hybrids as a potential “flexibility” option to introduce in the legislation.

An independent energy economics expert, who was not involved with the research, described the analysis a “highly valuable contribution” after years in which segments of the car industry claimed there was too little information to accurately assess real-world emissions.

“The results show, beyond any doubt, that the difference between official and actual PHEV fuel consumption and CO₂ emissions is much, much greater than for gasoline or diesel cars,” they said. “Any regulatory adjustments concerning PHEVs should be made with utmost care and in the light of this evidence.”