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Plug-in hybrid cars release almost 5x more global warming pollution than official data indicate, as per a new analysis.

Widening Discrepancy Between Lab and Real-World CO2 Output

Data reveals that PHEVs release only 19% less CO₂ than conventional petrol and diesel cars, according to research conducted by a non-profit group. That contrasts sharply with laboratory estimates, which assumed a 75% reduction in emissions.

Researchers examined data from in-vehicle fuel consumption meters of 800,000 vehicles registered in Europe between 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than official estimates, up from three and a half times in 2021.

“Actual CO2 output are rising, while official emissions are falling,” said a senior researcher participating in the study. “That gap is widening and poses a serious issue. Consequently, PHEVs emit almost as much as petrol cars.”

Key Reasons Behind the Discrepancy

Researchers attributed most of the difference to inflated estimates of the “utility factor” – the ratio of kilometers driven in battery mode relative to total distance. They found that only 27% of driving was done in electric mode, while official estimates suggested 84%.

Additionally, when operating in EV mode, pollution levels were significantly higher than lab projections. This occurred because electric motors were not strong sufficient to operate independently, leading to engines burning gasoline for almost one-third of the travel completed in EV mode.

Regulatory and Financial Consequences

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

Furthermore, drivers of PHEVs could pay approximately €500 extra per year in running costs than is assumed under lab tests.

“The strong statements that manufacturers often promote about their plug-in hybrid vehicles are obviously way off the truth,” commented a transport analyst. “Buyers are being duped into thinking that by buying a PHEV, they are benefiting the environment and cutting costs. In reality, PHEVs are little improved than standard gas and diesel vehicles in terms of energy consumption, CO₂ emissions, and operating costs.”

Political Debate and Automotive Pressure

Plug-in hybrid cars have lately been drawn again into political debates as automakers have pressed the EU to relax CO₂ targets. A planned prohibition on new combustion engine vehicles in 2035 has faced intense pressure from the automotive sector and resistance from member states with large car manufacturing.

Several high-level officials have suggested plug-in hybrids as a potential “flexibility” option to include in the legislation.

One external energy economics specialist, who was not involved with the study, called the analysis a “very useful contribution” after years in which segments of the car sector claimed there was insufficient data to accurately assess real-world CO2 output.

“The results demonstrate, without question, that the gap in official and actual PHEV fuel consumption and CO₂ emissions is much, much greater than for petrol or conventional vehicles,” the expert said. “All regulatory adjustments concerning PHEVs should be implemented with extreme care and considering that data.”