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Plug-in hybrid cars emit nearly five times more planet-heating pollution than official figures indicate, according to a new analysis.

Growing Discrepancy Between Official and Real-World CO2 Output

Statistics shows that PHEVs emit just 19% lower CO₂ than conventional petrol and diesel vehicles, based on analysis carried out by a advocacy organization. That differs significantly with lab estimates, which assumed a 75% decrease in emissions.

Researchers studied data from onboard fuel consumption monitors of 800,000 vehicles registered in Europe between 2021 and 2023. The team discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times higher than official figures, increased from 3.5 times in 2021.

“Actual emissions are rising, while lab-reported figures are falling,” said a lead analyst involved in the study. “That discrepancy is growing and creates a significant problem. Consequently, PHEVs emit almost as heavily as petrol vehicles.”

Primary Factors Behind the Emissions Gap

Researchers attributed the majority of the difference to inflated estimates of the “electric driving share” – the ratio of miles driven in electric power compared to total distance. The team found that only a quarter of driving was completed in EV mode, while official assumptions assumed over four-fifths.

Even, when operating in EV mode, pollution levels were well above official estimates. This occurred because EV motors were insufficiently powerful sufficient to function alone, leading to combustion motors using gasoline for nearly a third of the travel completed in EV mode.

Regulatory and Financial Implications

Based on estimates, the lowballing of PHEV CO2 output allowed four major automaker groups to avoid over €5bn in penalties between 2021 and 2023, by artificially simplifying adherence with EU fleet-average CO₂ targets.

Furthermore, drivers of PHEVs could pay approximately €500 more annually in operating expenses than is estimated under laboratory conditions.

“The strong claims that manufacturers like to make about their plug-in hybrid cars are obviously far from the truth,” commented a transport analyst. “Consumers are being misled into thinking that by purchasing a PHEV, they are helping the planet and cutting costs. Actually, PHEVs are little better than standard petrol and diesel vehicles in terms of fuel use, CO₂ production, and running costs.”

Policy Discussion and Automotive Pressure

Plug-in hybrid vehicles have lately been drawn back into political discussions as automakers have pressed the EU to weaken CO₂ targets. A proposed ban on new combustion engine vehicles in 2035 has faced heavy pressure from the automotive industry and resistance from EU countries with large automotive manufacturing.

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

An external energy economics specialist, who was not involved 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 assess actual CO2 output.

“These findings show, without question, that the gap in lab and actual PHEV fuel consumption and CO₂ output is much, much greater than for gasoline or conventional vehicles,” the expert said. “Any regulatory adjustments regarding PHEVs should be implemented with utmost caution and in the light of that data.”