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

Widening Gap In Official and Real-World CO2 Output

Data shows that PHEVs emit only 19% lower CO₂ than conventional petrol and diesel cars, according to analysis conducted by a advocacy organization. This differs sharply with laboratory tests, which assumed a three-quarters decrease in pollution.

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

“Actual CO2 output are rising, while lab-reported figures are decreasing,” stated a lead researcher involved in the report. “That gap is growing and poses a serious problem. Consequently, PHEVs emit nearly as much as gasoline cars.”

Key Reasons Driving the Emissions Gap

Researchers attributed the majority of the gap to inflated estimates of the “electric driving share” – the ratio of kilometers driven in battery power compared to overall mileage. They found that only a quarter of travel was completed in electric mode, while lab estimates suggested over four-fifths.

Additionally, when running in EV mode, emission levels were well above official estimates. That happened because electric motors were not strong enough to function independently, leading to combustion motors using gasoline for almost a third of the travel covered in electric mode.

Policy and Economic Consequences

Based on calculations, the underestimation of PHEV CO2 output enabled several large carmaker companies to avoid over €5bn in penalties from 2021 and 2023, by artificially easing adherence with European Union average fleet CO₂ targets.

Furthermore, owners of PHEVs could spend about €500 extra per year in running costs than would be assumed under laboratory conditions.

“The strong statements that automakers like to make about their PHEV vehicles are obviously way off the truth,” stated a transport expert. “Buyers are being misled into thinking that by buying a PHEV, they are helping the environment and cutting costs. In reality, PHEVs are only slightly better than regular gas and diesel vehicles in terms of fuel consumption, CO₂ emissions, and running expenses.”

Policy Discussion and Industry Lobbying

Hybrid vehicles have recently been drawn again into policy debates as carmakers have lobbied the EU to relax CO₂ standards. A proposed prohibition on sales of new internal combustion cars in 2035 has faced intense pressure from the automotive sector and resistance from member states with large car industries.

Several senior officials 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, described the analysis a “highly valuable addition” after years in which parts of the car industry claimed there was too little information to accurately assess real-world emissions.

“The results demonstrate, beyond any doubt, that the difference in lab and real-world PHEV energy use and CO₂ emissions is much, much greater than for gasoline or conventional vehicles,” the expert said. “All policy adjustments regarding PHEVs should be made with utmost caution and considering that evidence.”