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Plug-in hybrid cars produce almost 5x greater planet-heating emissions than official data indicate, according to a recent report.

Growing Gap Between Official and Actual CO2 Output

Data shows that PHEVs release just one-fifth less CO₂ than conventional petrol and diesel cars, based on analysis carried out by a non-profit organization. This differs significantly with laboratory estimates, which assumed a 75% reduction in emissions.

Analysts examined information from onboard fuel consumption monitors of 800,000 cars registered in Europe from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than official estimates, increased from 3.5 times in 2021.

“Actual emissions are increasing, while official figures are falling,” stated a lead researcher involved in the study. “That gap is growing and poses a serious problem. As a result, PHEVs pollute nearly as much as petrol vehicles.”

Primary Factors Driving the Discrepancy

Researchers linked the majority of the difference to overestimates of the “utility factor” – the percentage of miles driven in battery mode relative to total mileage. The team determined that just a quarter of travel was completed in EV mode, whereas official estimates suggested 84%.

Additionally, when running in EV mode, emission amounts were well above lab estimates. This happened because EV motors were not strong sufficient to operate alone, resulting to combustion motors using gasoline for nearly one-third of the distance completed in EV mode.

Policy and Financial Consequences

According to calculations, the lowballing of PHEV CO2 output allowed four major carmaker groups to escape over €5bn in fines between 2021 and 2023, by falsely easing adherence with European Union average fleet CO₂ targets.

Furthermore, drivers of PHEVs could pay approximately €500 more annually in operating costs than would be assumed under laboratory conditions.

“The strong statements that automakers like to make about their PHEV cars are clearly far from the mark,” stated a transport expert. “Consumers are being duped into believing that by purchasing a PHEV, they are helping the environment and cutting money. In reality, PHEVs are little improved than regular gas and diesel cars in terms of energy use, CO₂ emissions, and running expenses.”

Policy Debate and Industry Lobbying

Plug-in hybrid vehicles have recently been drawn again into political debates as automakers have pressed the European Union to relax CO₂ standards. A planned ban on sales of new internal combustion vehicles in 2035 has faced heavy lobbying from the car industry and opposition from member states with large automotive manufacturing.

Several senior officials have suggested PHEVs as a potential “flexibility” solution to introduce in the regulation.

An independent energy policy expert, who was unaffiliated with the research, called the report a “highly valuable addition” after years in which parts of the car industry claimed there was too little information to accurately assess real-world CO2 output.

“These findings demonstrate, beyond any doubt, that the difference in lab and real-world PHEV energy use and CO₂ emissions is significantly greater than for petrol or diesel cars,” the expert stated. “Any regulatory changes regarding PHEVs should be made with extreme caution and considering that evidence.”