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Plug-in hybrid electric vehicles produce almost five times more global warming emissions than official data indicate, according to a new analysis.

Growing Discrepancy Between Lab and Actual CO2 Output

Data shows that PHEVs release only 19% less CO₂ than traditional gas and diesel cars, according to analysis carried out by a advocacy group. That differs sharply with laboratory tests, which suggested a three-quarters decrease in emissions.

Analysts studied data from in-vehicle fuel consumption monitors of 800,000 cars registered in Europe from 2021 and 2023. The team discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times greater than lab estimates, increased from 3.5 times in 2021.

“Real-world emissions are rising, while official figures are decreasing,” stated a lead researcher participating in the study. “This discrepancy is growing and creates a serious issue. As a result, PHEVs emit nearly as much as petrol cars.”

Primary Factors Driving the Discrepancy

Researchers attributed most of the difference to overestimates of the “electric driving share” – the percentage of kilometers driven in battery power relative to total distance. They found that only 27% of driving was completed in electric mode, while official assumptions suggested 84%.

Additionally, when operating in EV mode, emission amounts were significantly higher than lab estimates. This happened because EV motors were insufficiently powerful enough to operate independently, resulting to combustion motors using gasoline for almost a third of the travel completed in electric mode.

Policy and Financial Consequences

Based on calculations, the underestimation of PHEV emissions allowed several major carmaker groups to avoid over €5bn in fines from 2021 and 2023, by artificially simplifying adherence with EU average fleet CO₂ standards.

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

“The strong claims that automakers often promote about their PHEV vehicles are clearly far from the truth,” stated a automotive analyst. “Consumers are being duped into thinking that by purchasing a PHEV, they are helping the environment and cutting costs. In reality, PHEVs are little improved than standard gas and diesel cars in terms of fuel consumption, CO₂ emissions, and operating expenses.”

Policy Debate and Automotive Pressure

Hybrid cars have recently been drawn back into policy discussions as carmakers have lobbied the EU to relax CO₂ targets. A proposed ban on new combustion engine vehicles in 2035 has faced intense pressure from the car industry and opposition from EU countries with significant automotive industries.

Several senior politicians have suggested plug-in hybrids as a possible “compromise” option to include in the regulation.

An external energy policy specialist, who was unaffiliated with the research, described the report a “highly valuable contribution” after a long period in which segments of the car industry claimed there was insufficient data to properly assess real-world CO2 output.

“These findings show, beyond any doubt, that the gap between lab and actual PHEV fuel consumption and CO₂ output is significantly larger than for petrol or conventional vehicles,” the expert stated. “All regulatory changes concerning PHEVs should be implemented with extreme care and considering that data.”