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Plug-in hybrid electric vehicles emit almost 5x more global warming emissions than lab-reported data show, according to a new report.

Widening Gap In Lab and Real-World Emissions

Statistics reveals that PHEVs release only 19% less CO₂ than traditional petrol and diesel cars, based on analysis carried out by a non-profit group. This contrasts significantly with laboratory tests, which assumed a 75% reduction in emissions.

Researchers examined information from in-vehicle energy use meters of 800,000 vehicles registered in Europe from 2021 and 2023. They discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than official figures, up from 3.5 times in 2021.

“Actual CO2 output are rising, while official emissions are falling,” said a senior researcher involved in the study. “This gap is widening and creates a significant problem. As a result, PHEVs pollute nearly as heavily as petrol vehicles.”

Key Reasons Driving the Emissions Gap

Analysts attributed the majority of the difference to inflated estimates of the “electric driving share” – the percentage of kilometers travelled in electric mode relative to total mileage. The team found that only a quarter of travel was done in electric mode, whereas official estimates assumed 84%.

Even, when running in electric mode, emission levels were well above lab projections. That occurred because electric motors were not strong sufficient to function alone, leading to engines burning gasoline for nearly a third of the distance completed in electric mode.

Regulatory and Financial Consequences

According to estimates, the lowballing of PHEV CO2 output enabled several major carmaker groups to avoid more than €5bn in penalties from 2021 and 2023, by artificially simplifying adherence with European Union average fleet CO₂ standards.

Additionally, drivers of PHEVs could spend approximately €500 extra annually in operating expenses than would be assumed under laboratory tests.

“The strong statements that automakers often promote about their PHEV vehicles are clearly way off the mark,” commented a automotive analyst. “Buyers are being misled into thinking that by purchasing a PHEV, they are benefiting the environment and cutting costs. Actually, PHEVs are little improved than standard petrol and diesel cars in terms of fuel consumption, CO₂ emissions, and operating expenses.”

Policy Discussion and Automotive Lobbying

Hybrid vehicles have recently been brought back into political debates as automakers have lobbied the European Union to weaken CO₂ targets. A planned ban on new combustion engine vehicles in 2035 has faced intense lobbying from the car sector and resistance from EU countries with large automotive manufacturing.

Some high-level officials have proposed PHEVs as a possible “compromise” solution to introduce in the regulation.

One external energy policy expert, who was not involved with the study, described the report a “very useful addition” after years in which segments of the car sector claimed there was insufficient data to accurately assess actual emissions.

“The results demonstrate, beyond any doubt, that the difference between lab and actual PHEV energy use and CO₂ output is much, much larger than for gasoline or diesel vehicles,” they said. “All policy adjustments regarding PHEVs should be made with extreme care and considering that evidence.”