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Plug-in hybrid electric vehicles release nearly 5x greater global warming pollution than lab-reported figures show, according to a recent report.

Growing Gap Between Official and Actual Emissions

Data reveals that PHEVs emit only one-fifth less CO₂ than conventional petrol and diesel vehicles, according to research conducted by a non-profit organization. This differs sharply with lab estimates, which assumed a three-quarters decrease in emissions.

Researchers studied information from onboard fuel consumption meters of eight hundred thousand vehicles registered in Europe between 2021 and 2023. They discovered that real-world CO₂ emissions from PHEVs in 2023 were 4.9 times higher than lab figures, up from 3.5 times in 2021.

“Real-world emissions are increasing, while lab-reported figures are decreasing,” said a senior analyst participating in the study. “That discrepancy is widening and creates a serious problem. Consequently, PHEVs emit almost as much as petrol vehicles.”

Key Reasons Driving the Discrepancy

Analysts attributed most of the difference to overestimates of the “electric driving share” – the percentage of kilometers travelled in electric power compared to total mileage. They determined that only 27% of driving was done in EV mode, while official estimates suggested over four-fifths.

Additionally, when running in EV mode, pollution levels were significantly higher than lab estimates. That occurred because electric motors were not strong enough to operate independently, leading to engines using gasoline for almost one-third of the distance covered in electric mode.

Regulatory and Economic Implications

According to calculations, the underestimation of PHEV emissions enabled several major automaker companies to escape more than €5bn in penalties between 2021 and 2023, by artificially easing adherence with European Union fleet-average CO₂ targets.

Furthermore, owners of PHEVs would pay approximately €500 more annually in running costs than is estimated under laboratory tests.

“The strong statements that manufacturers like to make about their PHEV cars are obviously way off the truth,” commented a automotive expert. “Consumers are being misled into believing that by purchasing a PHEV, they are helping the environment and saving costs. In reality, PHEVs are only slightly improved than regular gas and diesel vehicles in terms of energy use, CO₂ production, and operating costs.”

Policy Discussion and Industry Pressure

Plug-in hybrid cars have lately been drawn again into policy debates as carmakers have pressed the European Union to relax CO₂ standards. A proposed prohibition on new internal combustion cars in 2035 has faced heavy lobbying from the automotive industry and opposition from member states with significant car industries.

Several high-level officials have suggested PHEVs as a possible “compromise” option to include in the legislation.

One independent energy economics specialist, who was not involved with the research, described the analysis a “very useful contribution” after a long period in which segments of the automotive sector claimed there was too little information to properly evaluate actual emissions.

“These findings show, beyond any doubt, that the difference between lab and actual 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 made with extreme care and considering that evidence.”