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Plug-in hybrid cars produce nearly five times greater global warming pollution than official figures show, according to a new report.

Widening Gap Between Official and Actual CO2 Output

Data reveals that PHEVs emit just 19% lower CO₂ than conventional petrol and diesel cars, according to analysis carried out by a non-profit organization. That differs significantly with laboratory estimates, which assumed a three-quarters reduction in emissions.

Researchers studied data from onboard fuel consumption meters of eight hundred thousand cars registered in the EU between 2021 and 2023. They discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than lab estimates, increased from 3.5 times in 2021.

“Real-world CO2 output are increasing, while official emissions are decreasing,” said a senior researcher participating in the study. “That discrepancy is growing and creates a significant issue. Consequently, PHEVs emit nearly as heavily as petrol cars.”

Primary Factors Behind the Discrepancy

Researchers linked the majority of the gap to overestimates of the “electric driving share” – the percentage of miles travelled in battery power compared to overall mileage. They found that just a quarter of travel was done in EV mode, while official assumptions assumed over four-fifths.

Additionally, when operating in EV mode, emission levels were significantly higher than official estimates. This happened because electric motors were not strong enough to operate independently, leading to combustion motors burning fossil fuels for nearly a third of the travel completed in EV mode.

Regulatory and Financial Implications

Based on estimates, the underestimation of PHEV CO2 output enabled four large automaker companies to escape more than €5bn in penalties between 2021 and 2023, by falsely simplifying adherence with European Union average fleet CO₂ standards.

Furthermore, owners of PHEVs could pay approximately €500 extra per year in operating expenses than would be assumed under laboratory conditions.

“The strong statements that manufacturers like to make about their plug-in hybrid cars are obviously way off the mark,” commented a automotive analyst. “Consumers are being misled into believing that by buying a PHEV, they are helping the environment and cutting money. In reality, PHEVs are only slightly improved than standard gas and diesel cars in terms of energy consumption, CO₂ production, and operating costs.”

Policy Discussion and Automotive Pressure

Plug-in hybrid vehicles have lately been brought back into policy discussions as carmakers have pressed the European Union to relax CO₂ targets. A proposed prohibition on new combustion engine vehicles in 2035 has faced intense pressure from the automotive industry and resistance from member states with large car industries.

Some senior politicians have proposed PHEVs as a possible “flexibility” solution to introduce in the legislation.

An independent energy policy specialist, who was not involved with the research, called the report a “highly valuable addition” after years in which parts of the car industry argued there was insufficient information to properly evaluate actual CO2 output.

“The results demonstrate, without question, that the difference in official and real-world PHEV energy use and CO₂ output is significantly greater than for gasoline or diesel cars,” the expert said. “All policy changes concerning PHEVs should be made with extreme care and considering that data.”