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Plug-in hybrid cars emit nearly five times more planet-heating emissions than lab-reported data show, as per a new report.

Growing Gap In Official and Actual CO2 Output

Data shows that PHEVs release just one-fifth less CO₂ than conventional petrol and diesel cars, according to analysis conducted by a non-profit group. This contrasts sharply with laboratory estimates, which assumed a 75% decrease in emissions.

Researchers studied data from in-vehicle energy use monitors of 800,000 vehicles registered in the EU between 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than lab figures, increased from 3.5 times in 2021.

“Actual CO2 output are rising, while official figures are falling,” stated a lead analyst participating in the study. “That gap is widening and creates a significant problem. Consequently, PHEVs pollute nearly as much as petrol cars.”

Primary Reasons Driving the Emissions Gap

Analysts attributed the majority of the difference to inflated estimates of the “electric driving share” – the ratio of kilometers driven in battery mode relative to total distance. They determined that only 27% of travel was done in EV mode, while official estimates assumed over four-fifths.

Additionally, when operating in electric mode, emission amounts were well above official estimates. This happened because electric motors were not strong enough to function independently, resulting to engines burning fossil fuels for almost one-third of the travel completed in EV mode.

Regulatory and Financial Consequences

Based on estimates, the underestimation of PHEV CO2 output allowed four large automaker companies to avoid more than €5bn in fines between 2021 and 2023, by falsely easing compliance with European Union fleet-average CO₂ targets.

Additionally, drivers of PHEVs would pay approximately €500 more annually in operating costs than is estimated under lab tests.

“The strong claims that manufacturers often promote about their PHEV cars are obviously far from the mark,” commented a transport expert. “Buyers are being misled into thinking that by purchasing a PHEV, they are helping the planet and cutting costs. Actually, PHEVs are only slightly better than regular petrol and diesel vehicles in terms of energy use, CO₂ emissions, and operating expenses.”

Policy Discussion and Automotive Pressure

Plug-in hybrid vehicles have recently been brought again into policy discussions as carmakers have lobbied the EU to weaken CO₂ standards. A planned prohibition on sales of new internal combustion cars in 2035 has faced intense pressure from the automotive industry and opposition from member states with significant automotive industries.

Some high-level politicians have proposed plug-in hybrids as a potential “compromise” option to include in the legislation.

An independent energy economics specialist, who was unaffiliated with the study, called the report a “highly valuable contribution” after years in which segments of the automotive sector claimed there was too little information to accurately assess real-world CO2 output.

“The results demonstrate, without question, that the gap between lab and actual PHEV energy use and CO₂ emissions is significantly greater than for petrol or diesel cars,” the expert said. “Any policy adjustments regarding PHEVs should be implemented with extreme caution and considering that data.”