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Plug-in hybrid cars emit almost 5x greater planet-heating pollution than lab-reported data show, according to a new analysis.

Widening Gap In Official and Real-World Emissions

Statistics reveals that PHEVs emit just one-fifth lower CO₂ than conventional gas and diesel cars, based on analysis carried out by a advocacy organization. This differs sharply with lab estimates, which assumed a three-quarters decrease in emissions.

Researchers examined information from onboard fuel consumption meters of 800,000 cars sold in the EU from 2021 and 2023. They discovered that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, increased from 3.5 times in 2021.

“Real-world CO2 output are increasing, while official figures are falling,” said a senior analyst participating in the study. “That discrepancy is widening and creates a serious problem. As a result, PHEVs emit almost as heavily as petrol vehicles.”

Primary Factors Driving the Discrepancy

Analysts linked most of the gap to inflated estimates of the “electric driving share” – the ratio of kilometers travelled in battery power relative to overall mileage. The team found that only 27% of travel was done in electric mode, while official estimates suggested over four-fifths.

Additionally, when running in EV mode, pollution levels were significantly higher than lab estimates. This happened because EV motors were insufficiently powerful sufficient to function independently, resulting to combustion motors using fossil fuels for nearly a third of the distance completed in electric mode.

Policy and Economic Consequences

Based on calculations, the underestimation of PHEV CO2 output allowed four large automaker groups to escape over €5bn in penalties from 2021 and 2023, by artificially simplifying compliance with European Union fleet-average CO₂ targets.

Additionally, drivers of PHEVs could spend about €500 more per year in running expenses than is estimated under laboratory tests.

“The strong statements that manufacturers often promote about their plug-in hybrid vehicles are clearly far from the mark,” stated a transport analyst. “Buyers are being misled into thinking that by purchasing a PHEV, they are helping the environment and saving costs. Actually, PHEVs are little better than standard petrol and diesel vehicles in terms of fuel use, CO₂ production, and operating costs.”

Policy Debate and Industry Pressure

Hybrid vehicles have lately been drawn back into policy debates as carmakers have lobbied the EU to relax CO₂ standards. A planned ban on new combustion engine cars in 2035 has faced intense pressure from the automotive industry and opposition from member states with large automotive manufacturing.

Several high-level politicians have proposed PHEVs as a possible “flexibility” option to include in the legislation.

An independent energy policy specialist, who was not involved with the research, called the analysis a “highly valuable contribution” after years in which segments of the car industry argued there was insufficient information to accurately evaluate real-world emissions.

“The results show, beyond any doubt, that the difference between lab and real-world PHEV energy use and CO₂ emissions is much, much greater than for gasoline or conventional vehicles,” they said. “Any policy changes concerning PHEVs should be implemented with utmost caution and in the light of this evidence.”