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Plug-in hybrid cars release nearly five times more planet-heating pollution than official data show, as per a new analysis.

Growing Discrepancy Between Official and Actual Emissions

Data reveals that PHEVs emit only 19% less CO₂ than traditional petrol and diesel vehicles, according to research carried out by a non-profit organization. That differs significantly with laboratory estimates, which suggested a three-quarters decrease in emissions.

Researchers examined data from onboard energy use monitors of 800,000 cars sold in the EU between 2021 and 2023. They discovered that actual CO₂ output from PHEVs in 2023 were nearly five times higher than official figures, increased from three and a half times in 2021.

“Real-world CO2 output are increasing, while lab-reported figures are decreasing,” said a senior researcher participating in the study. “That discrepancy is widening and creates a significant issue. As a result, PHEVs emit nearly as much as petrol cars.”

Key Factors Behind the Discrepancy

Researchers attributed the majority of the gap to overestimates of the “electric driving share” – the ratio of miles driven in electric mode compared to total distance. The team determined that only a quarter of travel was completed in electric mode, whereas official estimates suggested over four-fifths.

Additionally, when operating in electric mode, pollution levels were significantly higher than official estimates. That occurred because electric motors were not strong enough to operate alone, leading to engines burning fossil fuels for almost one-third of the travel covered in electric mode.

Regulatory and Economic Consequences

According to estimates, the underestimation of PHEV emissions allowed four major automaker groups to avoid more than €5bn in fines between 2021 and 2023, by artificially easing adherence with European Union fleet-average CO₂ standards.

Additionally, owners of PHEVs could spend approximately €500 more annually in running costs than is assumed under laboratory conditions.

“The strong claims that automakers like to make about their plug-in hybrid vehicles are clearly far from the mark,” stated a automotive expert. “Buyers are being duped into thinking that by buying a PHEV, they are helping the environment and saving costs. Actually, PHEVs are only slightly improved than standard petrol and diesel cars in terms of energy use, CO₂ production, and operating expenses.”

Policy Debate and Industry Lobbying

Plug-in hybrid cars have lately been drawn again into policy discussions as automakers have lobbied the EU to relax CO₂ standards. A planned ban on sales of new combustion engine vehicles in 2035 has faced intense pressure from the car sector and resistance from EU countries with significant car manufacturing.

Some senior officials have proposed plug-in hybrids as a possible “compromise” option to introduce in the regulation.

An external energy economics expert, who was unaffiliated with the research, called the analysis a “very useful contribution” after a long period in which parts of the car industry claimed there was too little data to properly evaluate actual emissions.

“The results show, beyond any doubt, that the gap in official and real-world PHEV energy use and CO₂ output is significantly larger than for petrol or diesel vehicles,” the expert stated. “Any policy changes regarding PHEVs should be made with utmost care and in the light of that evidence.”