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Plug-in hybrid cars emit nearly five times greater global warming pollution than lab-reported data indicate, according to a new report.

Widening Gap Between Official and Real-World CO2 Output

Data shows that PHEVs release only one-fifth less CO₂ than conventional gas and diesel vehicles, according to analysis conducted by a non-profit organization. This differs sharply with laboratory tests, which assumed a 75% decrease in emissions.

Analysts examined data from in-vehicle fuel consumption monitors of eight hundred thousand vehicles sold in the EU between 2021 and 2023. The team found that real-world CO₂ emissions from PHEVs in 2023 were nearly five times higher than lab estimates, increased from 3.5 times in 2021.

“Real-world emissions are increasing, while official figures are decreasing,” stated a senior analyst participating in the report. “That gap is growing and poses a serious problem. As a result, PHEVs pollute nearly as much as petrol cars.”

Key Factors Driving the Emissions Gap

Analysts attributed most of the gap to overestimates of the “electric driving share” – the ratio of miles driven in electric mode compared to overall distance. They found that just a quarter of travel was completed in electric mode, whereas lab assumptions suggested 84%.

Even, when operating in EV mode, emission amounts were significantly higher than official projections. This happened because EV motors were insufficiently powerful sufficient to operate independently, leading to engines burning gasoline for almost a third of the distance completed in electric mode.

Policy and Economic Consequences

Based on estimates, the underestimation of PHEV CO2 output allowed four major automaker groups to escape more than €5bn in fines between 2021 and 2023, by falsely simplifying adherence with EU fleet-average CO₂ standards.

Furthermore, owners of PHEVs could pay approximately €500 extra annually in operating expenses than would be assumed under laboratory tests.

“The bold claims that automakers like to make about their PHEV cars are obviously way off the truth,” stated a transport expert. “Consumers are being duped into thinking that by purchasing a PHEV, they are helping the environment and saving money. In reality, PHEVs are little improved than regular gas and diesel cars in terms of fuel use, CO₂ emissions, and operating costs.”

Policy Debate and Industry Lobbying

Hybrid vehicles have recently been brought back into policy discussions as carmakers have lobbied the EU to relax CO₂ targets. A planned ban on new combustion engine vehicles in 2035 has faced intense lobbying from the automotive sector and resistance from member states with significant automotive manufacturing.

Several high-level officials have proposed plug-in hybrids as a possible “flexibility” option to introduce in the legislation.

One external energy economics expert, who was not involved with the study, described the report a “highly valuable contribution” after a long period in which segments of the car sector claimed there was insufficient data to accurately assess real-world emissions.

“These findings show, without question, that the difference between lab and real-world PHEV fuel consumption and CO₂ output is significantly greater than for petrol or diesel vehicles,” they said. “All policy adjustments concerning PHEVs should be made with extreme care and considering this evidence.”