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Plug-in hybrid electric vehicles produce nearly 5x greater planet-heating emissions than official data indicate, according to a new report.

Growing Gap In Official and Actual CO2 Output

Data reveals that PHEVs release just 19% less CO₂ than traditional gas and diesel cars, based on analysis carried out by a non-profit organization. That differs significantly with lab estimates, which assumed a 75% decrease in emissions.

Analysts studied information from onboard energy use meters of 800,000 vehicles registered in the EU from 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than official figures, up from three and a half times in 2021.

“Actual emissions are rising, while lab-reported figures are falling,” said a senior researcher participating in the report. “That discrepancy is growing and poses a significant problem. Consequently, PHEVs pollute nearly as much as gasoline vehicles.”

Primary Reasons Driving the Emissions Gap

Analysts linked most of the difference to inflated estimates of the “utility factor” – the ratio of kilometers travelled in battery power compared to overall mileage. The team determined that only a quarter of travel was done in electric mode, while lab assumptions suggested 84%.

Additionally, when operating in electric mode, emission amounts were well above lab projections. This occurred because electric motors were not strong sufficient to operate independently, leading to engines burning fossil fuels for nearly one-third of the travel completed in EV mode.

Policy and Financial Consequences

Based on estimates, the underestimation of PHEV CO2 output enabled several large carmaker groups to avoid more than €5bn in penalties from 2021 and 2023, by artificially easing compliance with European Union fleet-average CO₂ targets.

Additionally, drivers of PHEVs could pay approximately €500 extra annually in running costs than would be estimated under lab conditions.

“The strong claims that manufacturers like to make about their PHEV vehicles are obviously far from the mark,” commented a transport expert. “Buyers are being misled into believing that by buying a PHEV, they are benefiting the planet and saving money. Actually, PHEVs are little better than regular gas and diesel cars in terms of energy consumption, CO₂ production, and operating expenses.”

Political Discussion and Industry Pressure

Hybrid cars have lately been drawn again into political discussions as carmakers have lobbied the European Union to relax CO₂ standards. A proposed ban on sales of new combustion engine cars in 2035 has faced intense lobbying from the car sector and resistance from EU countries with significant automotive manufacturing.

Some high-level officials have proposed plug-in hybrids as a potential “flexibility” option to introduce in the regulation.

One independent energy economics specialist, who was not involved with the research, described the report a “very useful addition” after years in which parts of the automotive sector claimed there was too little information to accurately assess real-world emissions.

“The results demonstrate, beyond any doubt, that the gap between lab and actual PHEV energy use and CO₂ emissions is much, much greater than for gasoline or conventional vehicles,” the expert stated. “Any policy changes regarding PHEVs should be made with extreme caution and considering this data.”