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Plug-in hybrid electric vehicles emit almost five times greater global warming pollution than lab-reported figures indicate, according to a new analysis.

Widening Discrepancy Between Official and Actual Emissions

Data reveals that PHEVs release only one-fifth lower CO₂ than conventional gas and diesel cars, based on analysis carried out by a non-profit organization. This contrasts sharply with lab tests, which suggested a three-quarters reduction in pollution.

Researchers studied information from onboard fuel consumption monitors of 800,000 cars sold in Europe from 2021 and 2023. They discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, increased from three and a half times in 2021.

“Real-world CO2 output are increasing, while lab-reported emissions are falling,” stated a senior analyst participating in the report. “This discrepancy is growing and poses a significant issue. Consequently, PHEVs pollute nearly as heavily as gasoline cars.”

Primary Factors Driving the Discrepancy

Analysts linked the majority of the difference to overestimates of the “electric driving share” – the ratio of kilometers travelled in battery mode compared to total mileage. The team found that only a quarter of travel was done in electric mode, whereas official estimates assumed 84%.

Additionally, when running in electric mode, pollution levels were well above official projections. That occurred because electric motors were insufficiently powerful enough to operate alone, leading to combustion motors burning gasoline for nearly a third of the travel completed in electric mode.

Regulatory and Financial Consequences

Based on estimates, the lowballing of PHEV emissions enabled several major automaker companies to escape over €5bn in fines between 2021 and 2023, by artificially simplifying compliance with European Union average fleet CO₂ targets.

Additionally, owners of PHEVs could pay about €500 extra per year in operating costs than is estimated under lab conditions.

“The bold claims that automakers like to make about their plug-in hybrid cars are obviously far from the truth,” commented a transport expert. “Consumers are being duped into believing that by buying a PHEV, they are benefiting the environment and saving money. Actually, PHEVs are little improved than regular petrol and diesel cars in terms of energy consumption, CO₂ production, and operating costs.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have recently been brought again into policy discussions as carmakers have pressed the European Union to weaken CO₂ standards. A proposed ban on sales of new combustion engine vehicles in 2035 has faced heavy pressure from the car sector and opposition from EU countries with significant automotive industries.

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

One external energy policy specialist, who was unaffiliated with the study, described the analysis a “very useful contribution” after years in which parts of the automotive sector argued there was insufficient information to properly assess actual emissions.

“The results show, beyond any doubt, that the gap in official and actual PHEV energy use and CO₂ emissions is much, much greater than for petrol or diesel vehicles,” the expert stated. “All policy changes concerning PHEVs should be implemented with extreme care and in the light of that data.”