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Plug-in hybrid electric vehicles produce almost 5x greater global warming pollution than official figures indicate, according to a new analysis.

Widening Gap Between Official and Actual Emissions

Statistics shows that PHEVs release just 19% lower CO₂ than traditional petrol and diesel vehicles, according to research carried out by a non-profit organization. This differs sharply with laboratory tests, which assumed a 75% decrease in emissions.

Researchers studied data from onboard energy use monitors of 800,000 vehicles sold in the EU from 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than official estimates, up from 3.5 times in 2021.

“Real-world emissions are rising, while lab-reported emissions are decreasing,” said a lead analyst involved in the study. “This discrepancy is widening and creates a serious problem. As a result, PHEVs pollute nearly as heavily as petrol vehicles.”

Key Reasons Driving the Discrepancy

Analysts linked the majority of the gap to overestimates of the “electric driving share” – the ratio of miles driven in battery power relative to overall mileage. The team determined that just 27% of travel was completed in electric mode, while official assumptions assumed over four-fifths.

Additionally, when running in EV mode, pollution amounts were well above official estimates. That happened because electric motors were insufficiently powerful enough to function independently, leading to combustion motors using fossil fuels for almost a third of the distance covered in EV mode.

Regulatory and Financial Implications

Based on calculations, the lowballing of PHEV emissions allowed four major carmaker groups to avoid more than €5bn in penalties between 2021 and 2023, by artificially simplifying compliance with EU fleet-average CO₂ targets.

Furthermore, owners of PHEVs could spend approximately €500 extra annually in operating costs than is estimated under lab tests.

“The strong claims that automakers often promote about their PHEV vehicles are clearly way off the truth,” stated a transport analyst. “Buyers are being duped into believing that by buying a PHEV, they are benefiting the planet and cutting costs. In reality, PHEVs are only slightly better than regular petrol and diesel cars in terms of fuel use, CO₂ production, and operating costs.”

Policy Debate and Automotive Pressure

Plug-in hybrid cars have lately been brought back into policy debates as automakers have lobbied the European Union to relax CO₂ standards. A planned prohibition on sales of new internal combustion cars in 2035 has faced heavy pressure from the car industry and opposition from member states with significant automotive industries.

Some senior officials have suggested plug-in hybrids as a possible “compromise” solution to include in the regulation.

An independent energy policy specialist, who was not involved with the research, called the report a “very useful addition” after years in which segments of the automotive industry claimed there was too little information to properly evaluate actual CO2 output.

“These findings show, beyond any doubt, that the gap in official and real-world PHEV fuel consumption and CO₂ emissions is significantly greater than for gasoline or conventional vehicles,” they said. “All policy adjustments concerning PHEVs should be made with extreme care and in the light of this evidence.”