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Plug-in hybrid cars produce nearly 5x more global warming emissions than lab-reported data indicate, as per a new report.

Widening Gap In Official and Actual CO2 Output

Data shows that PHEVs emit just 19% less CO₂ than conventional petrol and diesel vehicles, according to research conducted by a non-profit organization. That contrasts significantly with laboratory estimates, which assumed a 75% reduction in pollution.

Analysts examined data from in-vehicle fuel consumption monitors of 800,000 vehicles registered in Europe between 2021 and 2023. They discovered that actual CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab figures, up from three and a half times in 2021.

“Actual CO2 output are increasing, while official figures are decreasing,” said a lead analyst participating in the study. “That discrepancy is widening and creates a serious issue. Consequently, PHEVs emit nearly as heavily as gasoline vehicles.”

Primary Factors Driving the Discrepancy

Researchers attributed most of the difference to inflated estimates of the “electric driving share” – the ratio of kilometers driven in battery power compared to total distance. They found that only a quarter of travel was completed in electric mode, while official assumptions suggested 84%.

Even, when operating in electric mode, emission levels were well above official projections. This happened because electric motors were not strong enough to function alone, resulting to combustion motors using gasoline for nearly a third of the travel covered in electric mode.

Policy and Economic Implications

Based on estimates, the underestimation of PHEV emissions allowed several large carmaker groups to escape over €5bn in penalties between 2021 and 2023, by artificially easing adherence with EU average fleet CO₂ standards.

Furthermore, owners of PHEVs would spend about €500 more annually in running costs than would be assumed under laboratory tests.

“The bold statements that automakers often promote about their PHEV cars are clearly way off the mark,” stated a transport analyst. “Buyers are being misled into believing that by buying a PHEV, they are helping the environment and cutting costs. Actually, PHEVs are only slightly improved than regular gas and diesel vehicles in terms of fuel consumption, CO₂ emissions, and running expenses.”

Policy Debate and Automotive Pressure

Plug-in hybrid vehicles have recently been brought again into policy discussions as carmakers have pressed the European Union to relax CO₂ targets. A proposed ban on new internal combustion cars in 2035 has faced heavy pressure from the car industry and opposition from member states with significant car manufacturing.

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

One external energy policy specialist, who was not involved with the research, described the analysis a “highly valuable addition” after a long period in which segments of the car industry argued there was insufficient information to accurately evaluate actual CO2 output.

“These findings show, beyond any doubt, that the difference between lab and actual PHEV energy use and CO₂ emissions is significantly greater than for petrol or diesel cars,” the expert stated. “All regulatory adjustments concerning PHEVs should be implemented with utmost caution and in the light of this data.”