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Plug-in hybrid cars emit nearly 5x greater global warming emissions than lab-reported data show, according to a new analysis.

Widening Gap Between Lab and Actual CO2 Output

Data shows that PHEVs release just one-fifth less CO₂ than conventional petrol and diesel cars, based on analysis carried out by a advocacy group. This differs significantly with lab estimates, which assumed a 75% reduction in pollution.

Analysts studied information from in-vehicle energy use monitors of 800,000 vehicles sold in the EU from 2021 and 2023. The team found that real-world CO₂ output from PHEVs in 2023 were nearly five times higher than official estimates, up from three and a half times in 2021.

“Real-world emissions are increasing, while official figures are falling,” stated a lead analyst participating in the report. “This discrepancy is growing and poses a serious issue. As a result, PHEVs pollute nearly as heavily as petrol cars.”

Primary Factors Driving the Emissions Gap

Researchers linked most of the difference to inflated estimates of the “electric driving share” – the ratio of kilometers driven in electric power compared to overall distance. The team determined that just 27% of travel was completed in EV mode, while official assumptions suggested 84%.

Even, when running in electric mode, emission levels were well above official projections. This happened because electric motors were not strong sufficient to operate alone, leading to engines burning gasoline for almost one-third of the distance completed in EV mode.

Regulatory and Financial Implications

Based on calculations, the underestimation of PHEV CO2 output allowed four major carmaker groups to escape more than €5bn in fines between 2021 and 2023, by artificially easing compliance with European Union fleet-average CO₂ targets.

Furthermore, owners of PHEVs could spend approximately €500 extra annually in operating costs than would be assumed under lab tests.

“The strong claims that automakers often promote about their plug-in hybrid vehicles are obviously far from the mark,” stated a transport expert. “Consumers are being misled into believing that by purchasing a PHEV, they are benefiting the planet and cutting costs. Actually, PHEVs are little improved than standard petrol and diesel cars in terms of energy use, CO₂ emissions, and operating costs.”

Political Discussion and Automotive Pressure

Hybrid cars have recently been brought back into policy discussions as automakers have lobbied the EU to relax CO₂ targets. A planned prohibition on new internal combustion vehicles in 2035 has faced heavy pressure from the car industry and resistance from member states with large car manufacturing.

Several high-level politicians have proposed PHEVs as a potential “flexibility” solution to include in the regulation.

One independent energy policy expert, who was unaffiliated with the research, called the analysis a “very useful addition” after a long period in which segments of the automotive industry claimed there was insufficient information to properly assess actual CO2 output.

“The results show, beyond any doubt, that the difference in lab and real-world PHEV fuel consumption and CO₂ output is significantly larger than for petrol or diesel cars,” the expert stated. “Any regulatory changes concerning PHEVs should be made with utmost caution and considering this evidence.”