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Plug-in hybrid cars release almost five times greater global warming pollution than lab-reported data show, according to a new analysis.

Growing Discrepancy In Official and Actual Emissions

Statistics shows that PHEVs release only one-fifth lower CO₂ than conventional gas and diesel cars, based on research conducted by a advocacy organization. That differs sharply with lab tests, which suggested a 75% decrease in emissions.

Researchers examined data from in-vehicle energy use meters of 800,000 vehicles registered in the EU between 2021 and 2023. They discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times greater than lab figures, increased from three and a half times in 2021.

“Real-world emissions are increasing, while lab-reported figures are falling,” said a senior researcher participating in the study. “This discrepancy is widening and poses a significant issue. As a result, PHEVs pollute almost as much as gasoline vehicles.”

Key Reasons Driving the Discrepancy

Researchers attributed most of the difference to overestimates of the “electric driving share” – the percentage of kilometers travelled in electric mode compared to overall mileage. They found that only 27% of travel was done in electric mode, while official assumptions assumed 84%.

Additionally, when operating in EV mode, emission amounts were well above official estimates. That occurred because EV motors were insufficiently powerful sufficient to function alone, leading to combustion motors burning fossil fuels for almost one-third of the distance covered in electric mode.

Regulatory and Economic Consequences

Based on estimates, the lowballing of PHEV CO2 output allowed several major carmaker groups to avoid more than €5bn in fines between 2021 and 2023, by artificially easing compliance with EU average fleet CO₂ standards.

Furthermore, drivers of PHEVs could pay about €500 more annually in operating costs than would be assumed under laboratory conditions.

“The strong statements that manufacturers like to make about their plug-in hybrid vehicles are obviously way off the mark,” stated a transport analyst. “Consumers are being misled into believing that by buying a PHEV, they are benefiting the planet and cutting money. In reality, PHEVs are little improved than standard gas and diesel vehicles in terms of fuel use, CO₂ production, and running costs.”

Policy Debate and Automotive Lobbying

Plug-in hybrid cars have recently been drawn back into policy debates as automakers have pressed the European Union to weaken CO₂ targets. A planned prohibition on sales of new combustion engine cars in 2035 has faced heavy pressure from the automotive sector and resistance from EU countries with large car manufacturing.

Several senior officials have suggested plug-in hybrids as a possible “flexibility” solution to introduce in the legislation.

One independent energy economics specialist, who was not involved with the study, described the report a “highly valuable contribution” after a long period in which parts of the automotive industry claimed there was too little information to accurately evaluate actual CO2 output.

“The results demonstrate, beyond any doubt, that the gap between official and actual PHEV energy use and CO₂ emissions is significantly larger than for petrol or diesel cars,” the expert said. “Any regulatory adjustments concerning PHEVs should be made with extreme care and in the light of that data.”