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Plug-in hybrid electric vehicles emit almost 5x greater global warming pollution than official data indicate, as per a new analysis.

Growing Gap Between Official and Real-World CO2 Output

Statistics reveals that PHEVs emit only 19% lower CO₂ than traditional gas and diesel vehicles, according to research carried out by a advocacy organization. This contrasts sharply with laboratory tests, which suggested a 75% decrease in emissions.

Researchers examined information from in-vehicle energy use monitors of 800,000 cars sold in the EU from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were 4.9 times greater than lab estimates, up from three and a half times in 2021.

“Real-world CO2 output are increasing, while official emissions are decreasing,” said a senior analyst participating in the study. “That discrepancy is widening and creates a significant issue. Consequently, PHEVs pollute almost as heavily as petrol vehicles.”

Primary Factors Driving the Discrepancy

Analysts linked the majority of the gap to overestimates of the “electric driving share” – the ratio of kilometers driven in battery mode relative to overall mileage. They determined that only 27% of driving was done in EV mode, while lab estimates suggested 84%.

Additionally, when operating in electric mode, emission amounts were significantly higher than official projections. This occurred because electric motors were not strong enough to operate alone, leading to combustion motors burning fossil fuels for nearly a third of the distance completed in EV mode.

Regulatory and Economic Consequences

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

Furthermore, drivers of PHEVs would spend about €500 extra per year in operating costs than would be estimated under laboratory conditions.

“The strong statements that manufacturers often promote about their plug-in hybrid vehicles are obviously far from the mark,” stated a transport expert. “Buyers are being misled into believing that by purchasing a PHEV, they are helping the environment and saving costs. Actually, PHEVs are only slightly better than standard gas and diesel cars in terms of fuel consumption, CO₂ emissions, and operating expenses.”

Policy Debate and Automotive Pressure

Plug-in hybrid cars have lately been brought back into political debates as automakers have lobbied the EU to weaken CO₂ targets. A proposed ban on new combustion engine cars in 2035 has faced intense lobbying from the car sector and resistance from EU countries with large car manufacturing.

Some senior politicians have suggested PHEVs as a possible “flexibility” option to introduce in the regulation.

An independent energy economics expert, who was unaffiliated with the research, called the analysis a “very useful contribution” after a long period in which parts of the car sector claimed there was insufficient data to accurately evaluate actual CO2 output.

“These findings show, beyond any doubt, that the gap between lab and actual PHEV energy use and CO₂ output is significantly larger than for petrol or conventional cars,” the expert said. “All regulatory adjustments concerning PHEVs should be made with utmost care and in the light of that data.”