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Plug-in hybrid cars release almost 5x more global warming pollution than lab-reported data indicate, according to a new analysis.

Growing Discrepancy Between Official and Real-World CO2 Output

Data reveals that PHEVs release just 19% lower CO₂ than conventional petrol and diesel vehicles, according to analysis carried out by a non-profit group. This differs sharply with laboratory estimates, which suggested a three-quarters decrease in pollution.

Researchers examined information from onboard energy use monitors of eight hundred thousand vehicles registered in the EU from 2021 and 2023. They found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab figures, up from 3.5 times in 2021.

“Real-world emissions are rising, while lab-reported figures are falling,” stated a lead researcher involved in the study. “That gap is growing and poses a significant issue. Consequently, PHEVs emit almost as heavily as petrol vehicles.”

Key Factors Behind the Discrepancy

Researchers attributed most of the difference to inflated estimates of the “utility factor” – the percentage of kilometers travelled in battery mode relative to overall distance. They determined that just 27% of driving was completed in electric mode, while official assumptions suggested over four-fifths.

Additionally, when running in electric mode, emission amounts were significantly higher than official projections. That happened because electric motors were not strong sufficient to operate alone, leading to combustion motors using gasoline for nearly a third of the travel covered in electric mode.

Regulatory and Economic Implications

Based on calculations, the underestimation of PHEV CO2 output allowed several major automaker companies to avoid more than €5bn in fines between 2021 and 2023, by falsely simplifying compliance with EU fleet-average CO₂ targets.

Furthermore, drivers of PHEVs would pay approximately €500 more per year in operating costs than is estimated under laboratory conditions.

“The bold claims that manufacturers like to make about their plug-in hybrid vehicles are obviously far from the truth,” stated a transport analyst. “Buyers are being misled into believing that by purchasing a PHEV, they are benefiting the environment and saving costs. Actually, PHEVs are only slightly better than standard gas and diesel vehicles in terms of fuel use, CO₂ emissions, and running expenses.”

Political Debate and Automotive Lobbying

Hybrid vehicles have recently been drawn again into political discussions as automakers have pressed the EU to relax CO₂ targets. A proposed prohibition on sales of new internal combustion vehicles in 2035 has faced intense pressure from the car industry and opposition from member states with large automotive manufacturing.

Several senior politicians have suggested plug-in hybrids as a potential “compromise” solution to introduce in the legislation.

One independent energy economics specialist, who was unaffiliated with the research, called the report a “highly valuable addition” after years in which parts of the car sector argued there was insufficient information to accurately assess actual CO2 output.

“The results show, beyond any doubt, that the difference in official and real-world PHEV fuel consumption and CO₂ emissions is much, much greater than for gasoline or conventional cars,” the expert said. “Any regulatory changes regarding PHEVs should be implemented with extreme care and in the light of that data.”